Mercury HoldCo Inc.

SEC source: 0000950157-26-000570 · form4.xml · derivative · entry 4

Akastor ASA · CIK 0002037057 · 10% owner

Akastor AS · CIK 0002124921 · Director · 10% owner · Director by Deputization

Mercury HoldCo AS · CIK 0002124920 · 10% owner

Mercury HoldCo Inc. · CIK 0002124922 · Director · 10% owner · Director by Deputization

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · Akastor AS See footnotes

Disclosed balance after: 15,945,826

Underlying: Class A common stock · 342,922 shares

Expires not disclosed

F1 · derivative.exercise_price: On April 30, 2026, the underwriters of the initial public offering of HMH Holding Inc. (the "Issuer") partially exercised their option to purchase (the "Over Allotment") additional shares of the Issuer's Class A Common Stock, par value $0.01 per share (the "Class A Common Stock"). In connection with the Over Allotment, the underwriters will purchase 685,844 shares of Class A Common Stock, and the transaction is anticipated to close on May 5, 2026. (cont'd in fn 2)

F2 · derivative.exercise_price: (cont'd from fn 1) The Issuer will contribute the net proceeds from the Over Allotment, which will amount to $12,893,867.20, to HMH Holding B.V. ("HMH B.V."), and HMH B.V. will use such net proceeds to purchase in equal proportion from Akastor (as defined below) and another stockholder of HMH B.V., respectively, an aggregate number of shares of Class B common stock of the Issuer (the "Issuer Class B Shares"), non-voting Class A ordinary shares in HMH B.V. (the "B.V. Non-Voting Class A Shares") and non-voting Class B shares in HMH B.V. (the "B.V. Non-Voting Class B Shares"), respectively, equal to the number of shares of Class A Common Stock to be purchased by the underwriters pursuant to the Over Allotment. (cont'd in fn 3)

F3 · derivative.exercise_price: (cont'd from fn 2) With regards to Akastor, HMH B.V. will purchase the following securities for a cumulative purchase price of $6,446,933.60 to be paid to Akastor: (i) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class A Shares from Mercury HoldCo Inc. in exchange for $2,773,200.59 and (ii) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class B Shares from Akastor AS in exchange for $3,673,733.01.

F5 · derivative.exercise_price: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Class A Common Stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · kind: On April 30, 2026, the underwriters of the initial public offering of HMH Holding Inc. (the "Issuer") partially exercised their option to purchase (the "Over Allotment") additional shares of the Issuer's Class A Common Stock, par value $0.01 per share (the "Class A Common Stock"). In connection with the Over Allotment, the underwriters will purchase 685,844 shares of Class A Common Stock, and the transaction is anticipated to close on May 5, 2026. (cont'd in fn 2)

F2 · kind: (cont'd from fn 1) The Issuer will contribute the net proceeds from the Over Allotment, which will amount to $12,893,867.20, to HMH Holding B.V. ("HMH B.V."), and HMH B.V. will use such net proceeds to purchase in equal proportion from Akastor (as defined below) and another stockholder of HMH B.V., respectively, an aggregate number of shares of Class B common stock of the Issuer (the "Issuer Class B Shares"), non-voting Class A ordinary shares in HMH B.V. (the "B.V. Non-Voting Class A Shares") and non-voting Class B shares in HMH B.V. (the "B.V. Non-Voting Class B Shares"), respectively, equal to the number of shares of Class A Common Stock to be purchased by the underwriters pursuant to the Over Allotment. (cont'd in fn 3)

F3 · kind: (cont'd from fn 2) With regards to Akastor, HMH B.V. will purchase the following securities for a cumulative purchase price of $6,446,933.60 to be paid to Akastor: (i) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class A Shares from Mercury HoldCo Inc. in exchange for $2,773,200.59 and (ii) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class B Shares from Akastor AS in exchange for $3,673,733.01.

F5 · kind: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Class A Common Stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · shares: On April 30, 2026, the underwriters of the initial public offering of HMH Holding Inc. (the "Issuer") partially exercised their option to purchase (the "Over Allotment") additional shares of the Issuer's Class A Common Stock, par value $0.01 per share (the "Class A Common Stock"). In connection with the Over Allotment, the underwriters will purchase 685,844 shares of Class A Common Stock, and the transaction is anticipated to close on May 5, 2026. (cont'd in fn 2)

F2 · shares: (cont'd from fn 1) The Issuer will contribute the net proceeds from the Over Allotment, which will amount to $12,893,867.20, to HMH Holding B.V. ("HMH B.V."), and HMH B.V. will use such net proceeds to purchase in equal proportion from Akastor (as defined below) and another stockholder of HMH B.V., respectively, an aggregate number of shares of Class B common stock of the Issuer (the "Issuer Class B Shares"), non-voting Class A ordinary shares in HMH B.V. (the "B.V. Non-Voting Class A Shares") and non-voting Class B shares in HMH B.V. (the "B.V. Non-Voting Class B Shares"), respectively, equal to the number of shares of Class A Common Stock to be purchased by the underwriters pursuant to the Over Allotment. (cont'd in fn 3)

F3 · shares: (cont'd from fn 2) With regards to Akastor, HMH B.V. will purchase the following securities for a cumulative purchase price of $6,446,933.60 to be paid to Akastor: (i) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class A Shares from Mercury HoldCo Inc. in exchange for $2,773,200.59 and (ii) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class B Shares from Akastor AS in exchange for $3,673,733.01.

F5 · shares: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Class A Common Stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · derivative.exercise_date: On April 30, 2026, the underwriters of the initial public offering of HMH Holding Inc. (the "Issuer") partially exercised their option to purchase (the "Over Allotment") additional shares of the Issuer's Class A Common Stock, par value $0.01 per share (the "Class A Common Stock"). In connection with the Over Allotment, the underwriters will purchase 685,844 shares of Class A Common Stock, and the transaction is anticipated to close on May 5, 2026. (cont'd in fn 2)

F2 · derivative.exercise_date: (cont'd from fn 1) The Issuer will contribute the net proceeds from the Over Allotment, which will amount to $12,893,867.20, to HMH Holding B.V. ("HMH B.V."), and HMH B.V. will use such net proceeds to purchase in equal proportion from Akastor (as defined below) and another stockholder of HMH B.V., respectively, an aggregate number of shares of Class B common stock of the Issuer (the "Issuer Class B Shares"), non-voting Class A ordinary shares in HMH B.V. (the "B.V. Non-Voting Class A Shares") and non-voting Class B shares in HMH B.V. (the "B.V. Non-Voting Class B Shares"), respectively, equal to the number of shares of Class A Common Stock to be purchased by the underwriters pursuant to the Over Allotment. (cont'd in fn 3)

F3 · derivative.exercise_date: (cont'd from fn 2) With regards to Akastor, HMH B.V. will purchase the following securities for a cumulative purchase price of $6,446,933.60 to be paid to Akastor: (i) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class A Shares from Mercury HoldCo Inc. in exchange for $2,773,200.59 and (ii) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class B Shares from Akastor AS in exchange for $3,673,733.01.

F5 · derivative.exercise_date: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Class A Common Stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · derivative.expiration_date: On April 30, 2026, the underwriters of the initial public offering of HMH Holding Inc. (the "Issuer") partially exercised their option to purchase (the "Over Allotment") additional shares of the Issuer's Class A Common Stock, par value $0.01 per share (the "Class A Common Stock"). In connection with the Over Allotment, the underwriters will purchase 685,844 shares of Class A Common Stock, and the transaction is anticipated to close on May 5, 2026. (cont'd in fn 2)

F2 · derivative.expiration_date: (cont'd from fn 1) The Issuer will contribute the net proceeds from the Over Allotment, which will amount to $12,893,867.20, to HMH Holding B.V. ("HMH B.V."), and HMH B.V. will use such net proceeds to purchase in equal proportion from Akastor (as defined below) and another stockholder of HMH B.V., respectively, an aggregate number of shares of Class B common stock of the Issuer (the "Issuer Class B Shares"), non-voting Class A ordinary shares in HMH B.V. (the "B.V. Non-Voting Class A Shares") and non-voting Class B shares in HMH B.V. (the "B.V. Non-Voting Class B Shares"), respectively, equal to the number of shares of Class A Common Stock to be purchased by the underwriters pursuant to the Over Allotment. (cont'd in fn 3)

F3 · derivative.expiration_date: (cont'd from fn 2) With regards to Akastor, HMH B.V. will purchase the following securities for a cumulative purchase price of $6,446,933.60 to be paid to Akastor: (i) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class A Shares from Mercury HoldCo Inc. in exchange for $2,773,200.59 and (ii) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class B Shares from Akastor AS in exchange for $3,673,733.01.

F5 · derivative.expiration_date: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Class A Common Stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · ownership.nature: On April 30, 2026, the underwriters of the initial public offering of HMH Holding Inc. (the "Issuer") partially exercised their option to purchase (the "Over Allotment") additional shares of the Issuer's Class A Common Stock, par value $0.01 per share (the "Class A Common Stock"). In connection with the Over Allotment, the underwriters will purchase 685,844 shares of Class A Common Stock, and the transaction is anticipated to close on May 5, 2026. (cont'd in fn 2)

F2 · ownership.nature: (cont'd from fn 1) The Issuer will contribute the net proceeds from the Over Allotment, which will amount to $12,893,867.20, to HMH Holding B.V. ("HMH B.V."), and HMH B.V. will use such net proceeds to purchase in equal proportion from Akastor (as defined below) and another stockholder of HMH B.V., respectively, an aggregate number of shares of Class B common stock of the Issuer (the "Issuer Class B Shares"), non-voting Class A ordinary shares in HMH B.V. (the "B.V. Non-Voting Class A Shares") and non-voting Class B shares in HMH B.V. (the "B.V. Non-Voting Class B Shares"), respectively, equal to the number of shares of Class A Common Stock to be purchased by the underwriters pursuant to the Over Allotment. (cont'd in fn 3)

F3 · ownership.nature: (cont'd from fn 2) With regards to Akastor, HMH B.V. will purchase the following securities for a cumulative purchase price of $6,446,933.60 to be paid to Akastor: (i) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class A Shares from Mercury HoldCo Inc. in exchange for $2,773,200.59 and (ii) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class B Shares from Akastor AS in exchange for $3,673,733.01.

F4 · ownership.nature: In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". Akastor ASA has an indirect pecuniary interest in the securities held by each of Akastor AS and Mercury HoldCo Inc. Mercury HoldCo AS has an indirect pecuniary interest in the securities held by Mercury HoldCo Inc. Consequently, Akastor ASA may be deemed to share beneficial ownership in the securities held directly by Akastor AS, and Akastor ASA and Mercury HoldCo AS may be deemed to share beneficial ownership in the securities held directly by Mercury HoldCo Inc. The board of directors and officers of Akastor ASA, Mercury HoldCo Inc., Akastor AS and Mercury HoldCo AS disclaim beneficial ownership with respect to such securities.

F5 · ownership.nature: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Class A Common Stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F6 · ownership.nature: Karl Erik Kjelstad and Svein Oskar Stoknes are directors of the Issuer and were nominated for such roles by Akastor AS and Mercury HoldCo Inc. By virtue of their service on the Board of Directors of the Issuer, for purposes of Section 16, Akastor AS and Mercury HoldCo Inc. may be deemed to be a "director by deputization" of the Issuer.

SEC source: 0000950157-26-000570 · form4.xml · derivative · entry 3

Akastor ASA · CIK 0002037057 · 10% owner

Akastor AS · CIK 0002124921 · Director · 10% owner · Director by Deputization

Mercury HoldCo AS · CIK 0002124920 · 10% owner

Mercury HoldCo Inc. · CIK 0002124922 · Director · 10% owner · Director by Deputization

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · Mercury HoldCo Inc. See footnotes

Disclosed balance after: 15,945,826

Underlying: Class A common stock · 342,922 shares

Expires not disclosed

F1 · derivative.exercise_price: On April 30, 2026, the underwriters of the initial public offering of HMH Holding Inc. (the "Issuer") partially exercised their option to purchase (the "Over Allotment") additional shares of the Issuer's Class A Common Stock, par value $0.01 per share (the "Class A Common Stock"). In connection with the Over Allotment, the underwriters will purchase 685,844 shares of Class A Common Stock, and the transaction is anticipated to close on May 5, 2026. (cont'd in fn 2)

F2 · derivative.exercise_price: (cont'd from fn 1) The Issuer will contribute the net proceeds from the Over Allotment, which will amount to $12,893,867.20, to HMH Holding B.V. ("HMH B.V."), and HMH B.V. will use such net proceeds to purchase in equal proportion from Akastor (as defined below) and another stockholder of HMH B.V., respectively, an aggregate number of shares of Class B common stock of the Issuer (the "Issuer Class B Shares"), non-voting Class A ordinary shares in HMH B.V. (the "B.V. Non-Voting Class A Shares") and non-voting Class B shares in HMH B.V. (the "B.V. Non-Voting Class B Shares"), respectively, equal to the number of shares of Class A Common Stock to be purchased by the underwriters pursuant to the Over Allotment. (cont'd in fn 3)

F3 · derivative.exercise_price: (cont'd from fn 2) With regards to Akastor, HMH B.V. will purchase the following securities for a cumulative purchase price of $6,446,933.60 to be paid to Akastor: (i) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class A Shares from Mercury HoldCo Inc. in exchange for $2,773,200.59 and (ii) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class B Shares from Akastor AS in exchange for $3,673,733.01.

F5 · derivative.exercise_price: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Class A Common Stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · kind: On April 30, 2026, the underwriters of the initial public offering of HMH Holding Inc. (the "Issuer") partially exercised their option to purchase (the "Over Allotment") additional shares of the Issuer's Class A Common Stock, par value $0.01 per share (the "Class A Common Stock"). In connection with the Over Allotment, the underwriters will purchase 685,844 shares of Class A Common Stock, and the transaction is anticipated to close on May 5, 2026. (cont'd in fn 2)

F2 · kind: (cont'd from fn 1) The Issuer will contribute the net proceeds from the Over Allotment, which will amount to $12,893,867.20, to HMH Holding B.V. ("HMH B.V."), and HMH B.V. will use such net proceeds to purchase in equal proportion from Akastor (as defined below) and another stockholder of HMH B.V., respectively, an aggregate number of shares of Class B common stock of the Issuer (the "Issuer Class B Shares"), non-voting Class A ordinary shares in HMH B.V. (the "B.V. Non-Voting Class A Shares") and non-voting Class B shares in HMH B.V. (the "B.V. Non-Voting Class B Shares"), respectively, equal to the number of shares of Class A Common Stock to be purchased by the underwriters pursuant to the Over Allotment. (cont'd in fn 3)

F3 · kind: (cont'd from fn 2) With regards to Akastor, HMH B.V. will purchase the following securities for a cumulative purchase price of $6,446,933.60 to be paid to Akastor: (i) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class A Shares from Mercury HoldCo Inc. in exchange for $2,773,200.59 and (ii) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class B Shares from Akastor AS in exchange for $3,673,733.01.

F5 · kind: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Class A Common Stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · shares: On April 30, 2026, the underwriters of the initial public offering of HMH Holding Inc. (the "Issuer") partially exercised their option to purchase (the "Over Allotment") additional shares of the Issuer's Class A Common Stock, par value $0.01 per share (the "Class A Common Stock"). In connection with the Over Allotment, the underwriters will purchase 685,844 shares of Class A Common Stock, and the transaction is anticipated to close on May 5, 2026. (cont'd in fn 2)

F2 · shares: (cont'd from fn 1) The Issuer will contribute the net proceeds from the Over Allotment, which will amount to $12,893,867.20, to HMH Holding B.V. ("HMH B.V."), and HMH B.V. will use such net proceeds to purchase in equal proportion from Akastor (as defined below) and another stockholder of HMH B.V., respectively, an aggregate number of shares of Class B common stock of the Issuer (the "Issuer Class B Shares"), non-voting Class A ordinary shares in HMH B.V. (the "B.V. Non-Voting Class A Shares") and non-voting Class B shares in HMH B.V. (the "B.V. Non-Voting Class B Shares"), respectively, equal to the number of shares of Class A Common Stock to be purchased by the underwriters pursuant to the Over Allotment. (cont'd in fn 3)

F3 · shares: (cont'd from fn 2) With regards to Akastor, HMH B.V. will purchase the following securities for a cumulative purchase price of $6,446,933.60 to be paid to Akastor: (i) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class A Shares from Mercury HoldCo Inc. in exchange for $2,773,200.59 and (ii) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class B Shares from Akastor AS in exchange for $3,673,733.01.

F5 · shares: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Class A Common Stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · derivative.exercise_date: On April 30, 2026, the underwriters of the initial public offering of HMH Holding Inc. (the "Issuer") partially exercised their option to purchase (the "Over Allotment") additional shares of the Issuer's Class A Common Stock, par value $0.01 per share (the "Class A Common Stock"). In connection with the Over Allotment, the underwriters will purchase 685,844 shares of Class A Common Stock, and the transaction is anticipated to close on May 5, 2026. (cont'd in fn 2)

F2 · derivative.exercise_date: (cont'd from fn 1) The Issuer will contribute the net proceeds from the Over Allotment, which will amount to $12,893,867.20, to HMH Holding B.V. ("HMH B.V."), and HMH B.V. will use such net proceeds to purchase in equal proportion from Akastor (as defined below) and another stockholder of HMH B.V., respectively, an aggregate number of shares of Class B common stock of the Issuer (the "Issuer Class B Shares"), non-voting Class A ordinary shares in HMH B.V. (the "B.V. Non-Voting Class A Shares") and non-voting Class B shares in HMH B.V. (the "B.V. Non-Voting Class B Shares"), respectively, equal to the number of shares of Class A Common Stock to be purchased by the underwriters pursuant to the Over Allotment. (cont'd in fn 3)

F3 · derivative.exercise_date: (cont'd from fn 2) With regards to Akastor, HMH B.V. will purchase the following securities for a cumulative purchase price of $6,446,933.60 to be paid to Akastor: (i) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class A Shares from Mercury HoldCo Inc. in exchange for $2,773,200.59 and (ii) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class B Shares from Akastor AS in exchange for $3,673,733.01.

F5 · derivative.exercise_date: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Class A Common Stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · derivative.expiration_date: On April 30, 2026, the underwriters of the initial public offering of HMH Holding Inc. (the "Issuer") partially exercised their option to purchase (the "Over Allotment") additional shares of the Issuer's Class A Common Stock, par value $0.01 per share (the "Class A Common Stock"). In connection with the Over Allotment, the underwriters will purchase 685,844 shares of Class A Common Stock, and the transaction is anticipated to close on May 5, 2026. (cont'd in fn 2)

F2 · derivative.expiration_date: (cont'd from fn 1) The Issuer will contribute the net proceeds from the Over Allotment, which will amount to $12,893,867.20, to HMH Holding B.V. ("HMH B.V."), and HMH B.V. will use such net proceeds to purchase in equal proportion from Akastor (as defined below) and another stockholder of HMH B.V., respectively, an aggregate number of shares of Class B common stock of the Issuer (the "Issuer Class B Shares"), non-voting Class A ordinary shares in HMH B.V. (the "B.V. Non-Voting Class A Shares") and non-voting Class B shares in HMH B.V. (the "B.V. Non-Voting Class B Shares"), respectively, equal to the number of shares of Class A Common Stock to be purchased by the underwriters pursuant to the Over Allotment. (cont'd in fn 3)

F3 · derivative.expiration_date: (cont'd from fn 2) With regards to Akastor, HMH B.V. will purchase the following securities for a cumulative purchase price of $6,446,933.60 to be paid to Akastor: (i) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class A Shares from Mercury HoldCo Inc. in exchange for $2,773,200.59 and (ii) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class B Shares from Akastor AS in exchange for $3,673,733.01.

F5 · derivative.expiration_date: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Class A Common Stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · ownership.nature: On April 30, 2026, the underwriters of the initial public offering of HMH Holding Inc. (the "Issuer") partially exercised their option to purchase (the "Over Allotment") additional shares of the Issuer's Class A Common Stock, par value $0.01 per share (the "Class A Common Stock"). In connection with the Over Allotment, the underwriters will purchase 685,844 shares of Class A Common Stock, and the transaction is anticipated to close on May 5, 2026. (cont'd in fn 2)

F2 · ownership.nature: (cont'd from fn 1) The Issuer will contribute the net proceeds from the Over Allotment, which will amount to $12,893,867.20, to HMH Holding B.V. ("HMH B.V."), and HMH B.V. will use such net proceeds to purchase in equal proportion from Akastor (as defined below) and another stockholder of HMH B.V., respectively, an aggregate number of shares of Class B common stock of the Issuer (the "Issuer Class B Shares"), non-voting Class A ordinary shares in HMH B.V. (the "B.V. Non-Voting Class A Shares") and non-voting Class B shares in HMH B.V. (the "B.V. Non-Voting Class B Shares"), respectively, equal to the number of shares of Class A Common Stock to be purchased by the underwriters pursuant to the Over Allotment. (cont'd in fn 3)

F3 · ownership.nature: (cont'd from fn 2) With regards to Akastor, HMH B.V. will purchase the following securities for a cumulative purchase price of $6,446,933.60 to be paid to Akastor: (i) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class A Shares from Mercury HoldCo Inc. in exchange for $2,773,200.59 and (ii) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class B Shares from Akastor AS in exchange for $3,673,733.01.

F4 · ownership.nature: In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". Akastor ASA has an indirect pecuniary interest in the securities held by each of Akastor AS and Mercury HoldCo Inc. Mercury HoldCo AS has an indirect pecuniary interest in the securities held by Mercury HoldCo Inc. Consequently, Akastor ASA may be deemed to share beneficial ownership in the securities held directly by Akastor AS, and Akastor ASA and Mercury HoldCo AS may be deemed to share beneficial ownership in the securities held directly by Mercury HoldCo Inc. The board of directors and officers of Akastor ASA, Mercury HoldCo Inc., Akastor AS and Mercury HoldCo AS disclaim beneficial ownership with respect to such securities.

F5 · ownership.nature: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Class A Common Stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F6 · ownership.nature: Karl Erik Kjelstad and Svein Oskar Stoknes are directors of the Issuer and were nominated for such roles by Akastor AS and Mercury HoldCo Inc. By virtue of their service on the Board of Directors of the Issuer, for purposes of Section 16, Akastor AS and Mercury HoldCo Inc. may be deemed to be a "director by deputization" of the Issuer.

SEC source: 0000950157-26-000570 · form4.xml · nonDerivative · entry 2

Akastor ASA · CIK 0002037057 · 10% owner

Akastor AS · CIK 0002124921 · Director · 10% owner · Director by Deputization

Mercury HoldCo AS · CIK 0002124920 · 10% owner

Mercury HoldCo Inc. · CIK 0002124922 · Director · 10% owner · Director by Deputization

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · Akastor AS See footnotes

Disclosed balance after: 15,945,826

F1 · kind: On April 30, 2026, the underwriters of the initial public offering of HMH Holding Inc. (the "Issuer") partially exercised their option to purchase (the "Over Allotment") additional shares of the Issuer's Class A Common Stock, par value $0.01 per share (the "Class A Common Stock"). In connection with the Over Allotment, the underwriters will purchase 685,844 shares of Class A Common Stock, and the transaction is anticipated to close on May 5, 2026. (cont'd in fn 2)

F2 · kind: (cont'd from fn 1) The Issuer will contribute the net proceeds from the Over Allotment, which will amount to $12,893,867.20, to HMH Holding B.V. ("HMH B.V."), and HMH B.V. will use such net proceeds to purchase in equal proportion from Akastor (as defined below) and another stockholder of HMH B.V., respectively, an aggregate number of shares of Class B common stock of the Issuer (the "Issuer Class B Shares"), non-voting Class A ordinary shares in HMH B.V. (the "B.V. Non-Voting Class A Shares") and non-voting Class B shares in HMH B.V. (the "B.V. Non-Voting Class B Shares"), respectively, equal to the number of shares of Class A Common Stock to be purchased by the underwriters pursuant to the Over Allotment. (cont'd in fn 3)

F3 · kind: (cont'd from fn 2) With regards to Akastor, HMH B.V. will purchase the following securities for a cumulative purchase price of $6,446,933.60 to be paid to Akastor: (i) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class A Shares from Mercury HoldCo Inc. in exchange for $2,773,200.59 and (ii) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class B Shares from Akastor AS in exchange for $3,673,733.01.

F5 · kind: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Class A Common Stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · ownership.nature: On April 30, 2026, the underwriters of the initial public offering of HMH Holding Inc. (the "Issuer") partially exercised their option to purchase (the "Over Allotment") additional shares of the Issuer's Class A Common Stock, par value $0.01 per share (the "Class A Common Stock"). In connection with the Over Allotment, the underwriters will purchase 685,844 shares of Class A Common Stock, and the transaction is anticipated to close on May 5, 2026. (cont'd in fn 2)

F2 · ownership.nature: (cont'd from fn 1) The Issuer will contribute the net proceeds from the Over Allotment, which will amount to $12,893,867.20, to HMH Holding B.V. ("HMH B.V."), and HMH B.V. will use such net proceeds to purchase in equal proportion from Akastor (as defined below) and another stockholder of HMH B.V., respectively, an aggregate number of shares of Class B common stock of the Issuer (the "Issuer Class B Shares"), non-voting Class A ordinary shares in HMH B.V. (the "B.V. Non-Voting Class A Shares") and non-voting Class B shares in HMH B.V. (the "B.V. Non-Voting Class B Shares"), respectively, equal to the number of shares of Class A Common Stock to be purchased by the underwriters pursuant to the Over Allotment. (cont'd in fn 3)

F3 · ownership.nature: (cont'd from fn 2) With regards to Akastor, HMH B.V. will purchase the following securities for a cumulative purchase price of $6,446,933.60 to be paid to Akastor: (i) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class A Shares from Mercury HoldCo Inc. in exchange for $2,773,200.59 and (ii) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class B Shares from Akastor AS in exchange for $3,673,733.01.

F4 · ownership.nature: In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". Akastor ASA has an indirect pecuniary interest in the securities held by each of Akastor AS and Mercury HoldCo Inc. Mercury HoldCo AS has an indirect pecuniary interest in the securities held by Mercury HoldCo Inc. Consequently, Akastor ASA may be deemed to share beneficial ownership in the securities held directly by Akastor AS, and Akastor ASA and Mercury HoldCo AS may be deemed to share beneficial ownership in the securities held directly by Mercury HoldCo Inc. The board of directors and officers of Akastor ASA, Mercury HoldCo Inc., Akastor AS and Mercury HoldCo AS disclaim beneficial ownership with respect to such securities.

F5 · ownership.nature: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Class A Common Stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F6 · ownership.nature: Karl Erik Kjelstad and Svein Oskar Stoknes are directors of the Issuer and were nominated for such roles by Akastor AS and Mercury HoldCo Inc. By virtue of their service on the Board of Directors of the Issuer, for purposes of Section 16, Akastor AS and Mercury HoldCo Inc. may be deemed to be a "director by deputization" of the Issuer.

SEC source: 0000950157-26-000570 · form4.xml · nonDerivative · entry 1

Akastor ASA · CIK 0002037057 · 10% owner

Akastor AS · CIK 0002124921 · Director · 10% owner · Director by Deputization

Mercury HoldCo AS · CIK 0002124920 · 10% owner

Mercury HoldCo Inc. · CIK 0002124922 · Director · 10% owner · Director by Deputization

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · Mercury HoldCo Inc. See footnotes

Disclosed balance after: 16,117,287

F1 · kind: On April 30, 2026, the underwriters of the initial public offering of HMH Holding Inc. (the "Issuer") partially exercised their option to purchase (the "Over Allotment") additional shares of the Issuer's Class A Common Stock, par value $0.01 per share (the "Class A Common Stock"). In connection with the Over Allotment, the underwriters will purchase 685,844 shares of Class A Common Stock, and the transaction is anticipated to close on May 5, 2026. (cont'd in fn 2)

F2 · kind: (cont'd from fn 1) The Issuer will contribute the net proceeds from the Over Allotment, which will amount to $12,893,867.20, to HMH Holding B.V. ("HMH B.V."), and HMH B.V. will use such net proceeds to purchase in equal proportion from Akastor (as defined below) and another stockholder of HMH B.V., respectively, an aggregate number of shares of Class B common stock of the Issuer (the "Issuer Class B Shares"), non-voting Class A ordinary shares in HMH B.V. (the "B.V. Non-Voting Class A Shares") and non-voting Class B shares in HMH B.V. (the "B.V. Non-Voting Class B Shares"), respectively, equal to the number of shares of Class A Common Stock to be purchased by the underwriters pursuant to the Over Allotment. (cont'd in fn 3)

F3 · kind: (cont'd from fn 2) With regards to Akastor, HMH B.V. will purchase the following securities for a cumulative purchase price of $6,446,933.60 to be paid to Akastor: (i) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class A Shares from Mercury HoldCo Inc. in exchange for $2,773,200.59 and (ii) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class B Shares from Akastor AS in exchange for $3,673,733.01.

F5 · kind: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Class A Common Stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · ownership.nature: On April 30, 2026, the underwriters of the initial public offering of HMH Holding Inc. (the "Issuer") partially exercised their option to purchase (the "Over Allotment") additional shares of the Issuer's Class A Common Stock, par value $0.01 per share (the "Class A Common Stock"). In connection with the Over Allotment, the underwriters will purchase 685,844 shares of Class A Common Stock, and the transaction is anticipated to close on May 5, 2026. (cont'd in fn 2)

F2 · ownership.nature: (cont'd from fn 1) The Issuer will contribute the net proceeds from the Over Allotment, which will amount to $12,893,867.20, to HMH Holding B.V. ("HMH B.V."), and HMH B.V. will use such net proceeds to purchase in equal proportion from Akastor (as defined below) and another stockholder of HMH B.V., respectively, an aggregate number of shares of Class B common stock of the Issuer (the "Issuer Class B Shares"), non-voting Class A ordinary shares in HMH B.V. (the "B.V. Non-Voting Class A Shares") and non-voting Class B shares in HMH B.V. (the "B.V. Non-Voting Class B Shares"), respectively, equal to the number of shares of Class A Common Stock to be purchased by the underwriters pursuant to the Over Allotment. (cont'd in fn 3)

F3 · ownership.nature: (cont'd from fn 2) With regards to Akastor, HMH B.V. will purchase the following securities for a cumulative purchase price of $6,446,933.60 to be paid to Akastor: (i) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class A Shares from Mercury HoldCo Inc. in exchange for $2,773,200.59 and (ii) 171,461 Issuer Class B Shares and 342,922 B.V. Non-Voting Class B Shares from Akastor AS in exchange for $3,673,733.01.

F4 · ownership.nature: In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". Akastor ASA has an indirect pecuniary interest in the securities held by each of Akastor AS and Mercury HoldCo Inc. Mercury HoldCo AS has an indirect pecuniary interest in the securities held by Mercury HoldCo Inc. Consequently, Akastor ASA may be deemed to share beneficial ownership in the securities held directly by Akastor AS, and Akastor ASA and Mercury HoldCo AS may be deemed to share beneficial ownership in the securities held directly by Mercury HoldCo Inc. The board of directors and officers of Akastor ASA, Mercury HoldCo Inc., Akastor AS and Mercury HoldCo AS disclaim beneficial ownership with respect to such securities.

F5 · ownership.nature: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Class A Common Stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F6 · ownership.nature: Karl Erik Kjelstad and Svein Oskar Stoknes are directors of the Issuer and were nominated for such roles by Akastor AS and Mercury HoldCo Inc. By virtue of their service on the Board of Directors of the Issuer, for purposes of Section 16, Akastor AS and Mercury HoldCo Inc. may be deemed to be a "director by deputization" of the Issuer.

SEC source: 0000950157-26-000464 · form4.xml · derivative · entry 8

Akastor ASA · CIK 0002037057 · 10% owner

Akastor AS · CIK 0002124921 · Director · 10% owner · Director by Deputization

Mercury HoldCo AS · CIK 0002124920 · 10% owner

Mercury HoldCo Inc. · CIK 0002124922 · Director · 10% owner · Director by Deputization

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · Akastor AS

Disclosed balance after: 16,288,748

Underlying: Class A common stock · 16,288,748 shares

Expires not disclosed

F1 · derivative.exercise_price: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · derivative.exercise_price: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · derivative.exercise_price: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · derivative.exercise_price: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · kind: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · kind: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · kind: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · kind: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · derivative.exercise_date: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · derivative.exercise_date: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · derivative.exercise_date: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · derivative.exercise_date: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · derivative.expiration_date: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · derivative.expiration_date: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · derivative.expiration_date: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · derivative.expiration_date: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · ownership.nature: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · ownership.nature: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · ownership.nature: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F4 · ownership.nature: Akastor ASA has an indirect pecuniary interest in the securities held by each of Akastor AS and Mercury HoldCo Inc. Mercury HoldCo AS has an indirect pecuniary interest in the securities held by Mercury HoldCo Inc. Consequently, Akastor ASA may be deemed to share beneficial ownership in the securities held directly by Akastor AS, and Akastor ASA and Mercury HoldCo AS may be deemed to share beneficial ownership in the securities held directly by Mercury HoldCo Inc. The board of directors and officers of Akastor ASA, Mercury HoldCo Inc., Akastor AS and Mercury HoldCo AS disclaim beneficial ownership with respect to such securities.

F5 · ownership.nature: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F6 · ownership.nature: Karl Erik Kjelstad and Svein Oskar Stoknes are directors of the Issuer and were nominated for such roles by Akastor AS and Mercury HoldCo Inc. By virtue of their service on the Board of Directors of the Issuer, for purposes of Section 16, Akastor AS and Mercury HoldCo Inc. may be deemed to be a "director by deputization" of the Issuer.

SEC source: 0000950157-26-000464 · form4.xml · derivative · entry 7

Akastor ASA · CIK 0002037057 · 10% owner

Akastor AS · CIK 0002124921 · Director · 10% owner · Director by Deputization

Mercury HoldCo AS · CIK 0002124920 · 10% owner

Mercury HoldCo Inc. · CIK 0002124922 · Director · 10% owner · Director by Deputization

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · Mercury HoldCo Inc.

Disclosed balance after: 16,288,748

Underlying: Class A common stock · 16,288,748 shares

Expires not disclosed

F1 · derivative.exercise_price: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · derivative.exercise_price: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · derivative.exercise_price: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · derivative.exercise_price: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · kind: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · kind: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · kind: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · kind: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · derivative.exercise_date: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · derivative.exercise_date: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · derivative.exercise_date: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · derivative.exercise_date: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · derivative.expiration_date: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · derivative.expiration_date: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · derivative.expiration_date: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · derivative.expiration_date: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · ownership.nature: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · ownership.nature: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · ownership.nature: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F4 · ownership.nature: Akastor ASA has an indirect pecuniary interest in the securities held by each of Akastor AS and Mercury HoldCo Inc. Mercury HoldCo AS has an indirect pecuniary interest in the securities held by Mercury HoldCo Inc. Consequently, Akastor ASA may be deemed to share beneficial ownership in the securities held directly by Akastor AS, and Akastor ASA and Mercury HoldCo AS may be deemed to share beneficial ownership in the securities held directly by Mercury HoldCo Inc. The board of directors and officers of Akastor ASA, Mercury HoldCo Inc., Akastor AS and Mercury HoldCo AS disclaim beneficial ownership with respect to such securities.

F5 · ownership.nature: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F6 · ownership.nature: Karl Erik Kjelstad and Svein Oskar Stoknes are directors of the Issuer and were nominated for such roles by Akastor AS and Mercury HoldCo Inc. By virtue of their service on the Board of Directors of the Issuer, for purposes of Section 16, Akastor AS and Mercury HoldCo Inc. may be deemed to be a "director by deputization" of the Issuer.

SEC source: 0000950157-26-000464 · form4.xml · derivative · entry 6

Akastor ASA · CIK 0002037057 · 10% owner

Akastor AS · CIK 0002124921 · Director · 10% owner · Director by Deputization

Mercury HoldCo AS · CIK 0002124920 · 10% owner

Mercury HoldCo Inc. · CIK 0002124922 · Director · 10% owner · Director by Deputization

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · Akastor AS

Disclosed balance after: 0

Underlying: Class A common stock · 16,288,748 shares

Expires not disclosed

F1 · derivative.exercise_price: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · derivative.exercise_price: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · derivative.exercise_price: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · derivative.exercise_price: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · kind: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · kind: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · kind: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · kind: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · derivative.exercise_date: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · derivative.exercise_date: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · derivative.exercise_date: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · derivative.exercise_date: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · derivative.expiration_date: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · derivative.expiration_date: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · derivative.expiration_date: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · derivative.expiration_date: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · ownership.nature: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · ownership.nature: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · ownership.nature: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F4 · ownership.nature: Akastor ASA has an indirect pecuniary interest in the securities held by each of Akastor AS and Mercury HoldCo Inc. Mercury HoldCo AS has an indirect pecuniary interest in the securities held by Mercury HoldCo Inc. Consequently, Akastor ASA may be deemed to share beneficial ownership in the securities held directly by Akastor AS, and Akastor ASA and Mercury HoldCo AS may be deemed to share beneficial ownership in the securities held directly by Mercury HoldCo Inc. The board of directors and officers of Akastor ASA, Mercury HoldCo Inc., Akastor AS and Mercury HoldCo AS disclaim beneficial ownership with respect to such securities.

F5 · ownership.nature: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F6 · ownership.nature: Karl Erik Kjelstad and Svein Oskar Stoknes are directors of the Issuer and were nominated for such roles by Akastor AS and Mercury HoldCo Inc. By virtue of their service on the Board of Directors of the Issuer, for purposes of Section 16, Akastor AS and Mercury HoldCo Inc. may be deemed to be a "director by deputization" of the Issuer.

SEC source: 0000950157-26-000464 · form4.xml · derivative · entry 5

Akastor ASA · CIK 0002037057 · 10% owner

Akastor AS · CIK 0002124921 · Director · 10% owner · Director by Deputization

Mercury HoldCo AS · CIK 0002124920 · 10% owner

Mercury HoldCo Inc. · CIK 0002124922 · Director · 10% owner · Director by Deputization

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · Mercury HoldCo Inc.

Disclosed balance after: 0

Underlying: Class A common stock · 16,288,748 shares

Expires not disclosed

F1 · derivative.exercise_price: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · derivative.exercise_price: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · derivative.exercise_price: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · derivative.exercise_price: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · kind: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · kind: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · kind: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · kind: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · derivative.exercise_date: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · derivative.exercise_date: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · derivative.exercise_date: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · derivative.exercise_date: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · derivative.expiration_date: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · derivative.expiration_date: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · derivative.expiration_date: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · derivative.expiration_date: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · ownership.nature: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · ownership.nature: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · ownership.nature: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F4 · ownership.nature: Akastor ASA has an indirect pecuniary interest in the securities held by each of Akastor AS and Mercury HoldCo Inc. Mercury HoldCo AS has an indirect pecuniary interest in the securities held by Mercury HoldCo Inc. Consequently, Akastor ASA may be deemed to share beneficial ownership in the securities held directly by Akastor AS, and Akastor ASA and Mercury HoldCo AS may be deemed to share beneficial ownership in the securities held directly by Mercury HoldCo Inc. The board of directors and officers of Akastor ASA, Mercury HoldCo Inc., Akastor AS and Mercury HoldCo AS disclaim beneficial ownership with respect to such securities.

F5 · ownership.nature: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F6 · ownership.nature: Karl Erik Kjelstad and Svein Oskar Stoknes are directors of the Issuer and were nominated for such roles by Akastor AS and Mercury HoldCo Inc. By virtue of their service on the Board of Directors of the Issuer, for purposes of Section 16, Akastor AS and Mercury HoldCo Inc. may be deemed to be a "director by deputization" of the Issuer.

SEC source: 0000950157-26-000464 · form4.xml · derivative · entry 4

Akastor ASA · CIK 0002037057 · 10% owner

Akastor AS · CIK 0002124921 · Director · 10% owner · Director by Deputization

Mercury HoldCo AS · CIK 0002124920 · 10% owner

Mercury HoldCo Inc. · CIK 0002124922 · Director · 10% owner · Director by Deputization

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · Akastor AS

Disclosed balance after: 16,288,748

Underlying: Class A common stock · 1,050,000 shares

Expires not disclosed

F1 · derivative.exercise_price: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · derivative.exercise_price: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · derivative.exercise_price: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · derivative.exercise_price: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · kind: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · kind: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · kind: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · kind: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · derivative.exercise_date: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · derivative.exercise_date: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · derivative.exercise_date: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · derivative.exercise_date: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · derivative.expiration_date: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · derivative.expiration_date: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · derivative.expiration_date: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · derivative.expiration_date: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · ownership.nature: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · ownership.nature: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · ownership.nature: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F4 · ownership.nature: Akastor ASA has an indirect pecuniary interest in the securities held by each of Akastor AS and Mercury HoldCo Inc. Mercury HoldCo AS has an indirect pecuniary interest in the securities held by Mercury HoldCo Inc. Consequently, Akastor ASA may be deemed to share beneficial ownership in the securities held directly by Akastor AS, and Akastor ASA and Mercury HoldCo AS may be deemed to share beneficial ownership in the securities held directly by Mercury HoldCo Inc. The board of directors and officers of Akastor ASA, Mercury HoldCo Inc., Akastor AS and Mercury HoldCo AS disclaim beneficial ownership with respect to such securities.

F5 · ownership.nature: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F6 · ownership.nature: Karl Erik Kjelstad and Svein Oskar Stoknes are directors of the Issuer and were nominated for such roles by Akastor AS and Mercury HoldCo Inc. By virtue of their service on the Board of Directors of the Issuer, for purposes of Section 16, Akastor AS and Mercury HoldCo Inc. may be deemed to be a "director by deputization" of the Issuer.

SEC source: 0000950157-26-000464 · form4.xml · derivative · entry 3

Akastor ASA · CIK 0002037057 · 10% owner

Akastor AS · CIK 0002124921 · Director · 10% owner · Director by Deputization

Mercury HoldCo AS · CIK 0002124920 · 10% owner

Mercury HoldCo Inc. · CIK 0002124922 · Director · 10% owner · Director by Deputization

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · Mercury HoldCo Inc.

Disclosed balance after: 16,288,748

Underlying: Class A common stock · 1,050,000 shares

Expires not disclosed

F1 · derivative.exercise_price: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · derivative.exercise_price: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · derivative.exercise_price: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · derivative.exercise_price: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · kind: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · kind: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · kind: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · kind: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · derivative.exercise_date: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · derivative.exercise_date: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · derivative.exercise_date: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · derivative.exercise_date: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · derivative.expiration_date: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · derivative.expiration_date: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · derivative.expiration_date: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · derivative.expiration_date: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · ownership.nature: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · ownership.nature: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · ownership.nature: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F4 · ownership.nature: Akastor ASA has an indirect pecuniary interest in the securities held by each of Akastor AS and Mercury HoldCo Inc. Mercury HoldCo AS has an indirect pecuniary interest in the securities held by Mercury HoldCo Inc. Consequently, Akastor ASA may be deemed to share beneficial ownership in the securities held directly by Akastor AS, and Akastor ASA and Mercury HoldCo AS may be deemed to share beneficial ownership in the securities held directly by Mercury HoldCo Inc. The board of directors and officers of Akastor ASA, Mercury HoldCo Inc., Akastor AS and Mercury HoldCo AS disclaim beneficial ownership with respect to such securities.

F5 · ownership.nature: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F6 · ownership.nature: Karl Erik Kjelstad and Svein Oskar Stoknes are directors of the Issuer and were nominated for such roles by Akastor AS and Mercury HoldCo Inc. By virtue of their service on the Board of Directors of the Issuer, for purposes of Section 16, Akastor AS and Mercury HoldCo Inc. may be deemed to be a "director by deputization" of the Issuer.

SEC source: 0000950157-26-000464 · form4.xml · nonDerivative · entry 2

Akastor ASA · CIK 0002037057 · 10% owner

Akastor AS · CIK 0002124921 · Director · 10% owner · Director by Deputization

Mercury HoldCo AS · CIK 0002124920 · 10% owner

Mercury HoldCo Inc. · CIK 0002124922 · Director · 10% owner · Director by Deputization

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · Akastor AS See footnotes

Disclosed balance after: 16,288,748

F1 · kind: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · kind: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · kind: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · kind: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · ownership.nature: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · ownership.nature: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · ownership.nature: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F4 · ownership.nature: Akastor ASA has an indirect pecuniary interest in the securities held by each of Akastor AS and Mercury HoldCo Inc. Mercury HoldCo AS has an indirect pecuniary interest in the securities held by Mercury HoldCo Inc. Consequently, Akastor ASA may be deemed to share beneficial ownership in the securities held directly by Akastor AS, and Akastor ASA and Mercury HoldCo AS may be deemed to share beneficial ownership in the securities held directly by Mercury HoldCo Inc. The board of directors and officers of Akastor ASA, Mercury HoldCo Inc., Akastor AS and Mercury HoldCo AS disclaim beneficial ownership with respect to such securities.

F5 · ownership.nature: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F6 · ownership.nature: Karl Erik Kjelstad and Svein Oskar Stoknes are directors of the Issuer and were nominated for such roles by Akastor AS and Mercury HoldCo Inc. By virtue of their service on the Board of Directors of the Issuer, for purposes of Section 16, Akastor AS and Mercury HoldCo Inc. may be deemed to be a "director by deputization" of the Issuer.

SEC source: 0000950157-26-000464 · form4.xml · nonDerivative · entry 1

Akastor ASA · CIK 0002037057 · 10% owner

Akastor AS · CIK 0002124921 · Director · 10% owner · Director by Deputization

Mercury HoldCo AS · CIK 0002124920 · 10% owner

Mercury HoldCo Inc. · CIK 0002124922 · Director · 10% owner · Director by Deputization

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Indirect · Mercury HoldCo Inc. See footnotes

Disclosed balance after: 8,144,374

F1 · kind: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · kind: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · kind: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F5 · kind: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F1 · ownership.nature: Prior to the initial public offering ("IPO") of HMH Holding Inc. (the "Issuer"), (a) Akastor AS, a direct wholly owned subsidiary of Akastor ASA, held 50 Class B ordinary shares (the "B.V. Voting Class B Shares") of HMH Holding B.V. ("HMH B.V.") and (b) Mercury HoldCo Inc., an indirect wholly owned subsidiary of Akastor ASA (with Mercury HoldCo AS as an intermediary subsidiary between Akastor ASA and Mercury HoldCo Inc.) held 50 Class A ordinary shares (the "B.V. Voting Class A Shares") of HMH B.V. In this filing, Akastor ASA, Akastor AS, Mercury HoldCo AS and Mercury HoldCo Inc. are collectively referred to as "Akastor". (cont'd in fn 2)

F2 · ownership.nature: (cont'd from fn 1) In connection with the corporate reorganization and Akastor's participation in the synthetic secondary as described in the Issuer's Registration Statement on Form S-1 (Registration No. 333-281497), the following transactions have occurred: first, HMH B.V., the predecessor entity to the Issuer, underwent a 346,774.96 for 1 stock split, after which Akastor held 17,338,748 B.V. Voting Class B Shares (through Akastor AS) and 17,338,748 B.V. Voting Class A Shares (through Mercury HoldCo Inc.); second, HMH B.V. recapitalized to convert (i) 16,288,748 of Mercury HoldCo Inc.'s B.V. Voting Class A Shares to non-voting Class A ordinary shares (the "B.V. Non-Voting Class A Shares") and (ii) 16,288,748 of Akastor AS's B.V. Voting Class B Shares to non-voting Class B ordinary shares (the "B.V. Non-Voting Class B Shares"); (cont'd in fn 3)

F3 · ownership.nature: (cont'd from fn. 2) third, (i) Akastor AS sold 1,050,000 B.V. Voting Class B Shares, and Mercury HoldCo Inc. sold 1,050,000 B.V. Voting Class A Shares, in each case, to the Issuer in exchange cumulatively for $19,740,000 and (ii) each of Akastor AS and Mercury HoldCo Inc. received 8,144,374 shares of Class B common stock of the Issuer (the "Issuer Class B Shares") in exchange for relinquishing voting rights on their respective remaining 16,288,748 B.V. Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Voting Class A Shares (held by Mercury HoldCo Inc.) that were recapitalized into 16,288,748 B.V. Non-Voting Class B Shares (held by Akastor AS) and 16,288,748 B.V. Non-Voting Class A Shares (held by Mercury HoldCo Inc.), respectively.

F4 · ownership.nature: Akastor ASA has an indirect pecuniary interest in the securities held by each of Akastor AS and Mercury HoldCo Inc. Mercury HoldCo AS has an indirect pecuniary interest in the securities held by Mercury HoldCo Inc. Consequently, Akastor ASA may be deemed to share beneficial ownership in the securities held directly by Akastor AS, and Akastor ASA and Mercury HoldCo AS may be deemed to share beneficial ownership in the securities held directly by Mercury HoldCo Inc. The board of directors and officers of Akastor ASA, Mercury HoldCo Inc., Akastor AS and Mercury HoldCo AS disclaim beneficial ownership with respect to such securities.

F5 · ownership.nature: Pursuant to the Exchange Agreement, dated as of April 2, 2026, by and among the Issuer, HMH B.V. and the other parties thereto, Akastor has the right to exchange one Issuer Class B Share, one B.V. Non-Voting Class A Share and one B.V. Non-Voting Class B Share for cash or shares of the Issuer's Class A common stock on a one-for-one basis, subject to customary conversion rate adjustments (e.g. for stock splits, stock dividends and reclassifications). These rights are exercisable at any time after the conclusion of the Issuer's IPO lock-up period (i.e., September 27, 2026, unless the IPO lock-up is earlier released or waived by the underwriters of the Issuer's IPO) and do not expire.

F6 · ownership.nature: Karl Erik Kjelstad and Svein Oskar Stoknes are directors of the Issuer and were nominated for such roles by Akastor AS and Mercury HoldCo Inc. By virtue of their service on the Board of Directors of the Issuer, for purposes of Section 16, Akastor AS and Mercury HoldCo Inc. may be deemed to be a "director by deputization" of the Issuer.