Exter Neil

SEC source: 0001620014-25-000005 · form4-09242025_080901.xml · derivative · entry 1

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 18,000

Underlying: Common Stock · 18,000 shares

Expires 2035-09-21

F1 · derivative.exercise_date: The option shall vest as to 1/9 of the total award monthly with the first tranche vesting on October 1, 2025, subject to the reporting person's continued service to the Issuer on the applicable vesting date.

SEC source: 0001415889-25-022301 · form4-08192025_080831.xml · derivative · entry 1

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 16,000

Underlying: Common Stock · 16,000 shares

Expires 2035-08-16

F1 · derivative.exercise_date: The option vested as to 1/16th of the total award on March 3, 2025, and thereafter vested or vests as to an additional 1/16th of the total award on the monthly anniversary thereof, subject to the reporting person's continued service to the Issuer on each vesting date.

SEC source: 0000899243-22-023459 · doc4.xml · derivative · entry 1

Exter Neil · CIK 0001620014 · Director · 10% owner

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 10,000

Underlying: Common Stock · 10,000 shares

Expires 2032-06-16

F1 · derivative.exercise_date: The option was granted on June 17, 2022 for 10,000 shares. The shares underlying the option are scheduled to vest in full on the one year anniversary of the date of grant of the option (or, if earlier, the date of the next annual meeting of stockholders following the date of grant of the option), subject to the reporting person's continued service.

SEC source: 0001567619-22-013117 · doc1.xml · derivative · entry 4

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 18,400

Underlying: Common Stock · 18,400 shares

Expires 2032-06-15

F5 · derivative.exercise_date: Shares subject to the Option shall vest in full on the earlier of (i) the first anniversary of June 16, 2022 or (ii) immediately prior to the Annual Meeting following the date of grant subject to the Reporting Person remaining a Service Provider (as defined in the 2020 Plan) through the vesting date.

SEC source: 0001567619-22-013117 · doc1.xml · nonDerivative · entry 3

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 28,815

F4 · balance_after: Includes 5,200 Restricted Stock Units.

SEC source: 0001567619-22-013195 · doc1.xml · derivative · entry 1

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 15,000

Underlying: Common Stock · 15,000 shares

Expires 2032-06-15

F1 · derivative.exercise_date: 25% of the shares subject to such option vest and become exercisable on the first day of each calendar quarter for three calendar quarters beginning October 1st and the remaining 25% of the shares subject to such option vest and become exercisable on the earlier of (i) the one-year anniversary of June 16, 2022 or (ii) the next annual meeting of the stockholders, subject to the Reporting Person's continued service to the Issuer as a director through each such date or, if earlier, such annual meeting.

SEC source: 0000899243-22-022011 · doc4.xml · nonDerivative · entry 1

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnote

Disclosed balance after: 0

F1 · shares: On June 8, 2022, Third Rock Ventures III, L.P. ("TRV III") sold 419,901 shares of Common Stock of the Issuer in multiple transactions at prices ranging from $20.25 to $20.41, inclusive, at a weighted average price per share of $20.25. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (1).

F1 · price: On June 8, 2022, Third Rock Ventures III, L.P. ("TRV III") sold 419,901 shares of Common Stock of the Issuer in multiple transactions at prices ranging from $20.25 to $20.41, inclusive, at a weighted average price per share of $20.25. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (1).

F2 · balance_after: After the above transaction, TRV III owned 5,104,130 shares of Common Stock of the Issuer.

F3 · ownership.nature: The Reporting Person is a partner of each of TRV GP III, L.P. and Third Rock Ventures GP IV, L.P. which is the general partner of each of TRV III and Third Rock Ventures IV, L.P. ("TRV IV" and collectively with TRV III, "the Funds"), respectively. The Reporting Person disclaims beneficial ownership over the shares held by the Funds, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0001209191-21-044174 · doc4.xml · derivative · entry 1

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 13,286

Underlying: Common Stock · 13,286 shares

Expires 2031-06-28

F1 · derivative.exercise_date: 25% of the shares subject to such option vest and become exercisable on the first day of each calendar quarter following June 29, 2021 for three calendar quarters and the remaining 25% of the shares subject to such option vest and become exercisable on the earlier of (i) the one-year anniversary of June 29, 2021 or (ii) the next annual meeting of the stockholders, subject to the Reporting Person's continued service to the Issuer as a director through each such date or, if earlier, such annual meeting.

SEC source: 0001567619-21-012593 · doc1.xml · derivative · entry 4

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 12,659

Underlying: Common Stock · 12,659 shares

Expires 2031-06-21

F5 · derivative.exercise_date: Shares subject to the Option shall vest in full on the earlier of (i) the first anniversary of June 22, 2021 or (ii) immediately prior to the Annual Meeting following the date of grant subject to the Reporting Person remaining a Service Provider (as defined in the 2020 Plan) through the vesting date.

SEC source: 0001567619-21-012593 · doc1.xml · nonDerivative · entry 3

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 23,615

F4 · balance_after: Includes 3,617 Restricted Stock Units.

SEC source: 0000899243-21-022346 · doc4.xml · nonDerivative · entry 2

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnote

Disclosed balance after: 0

F4 · shares: On June 4, 2021, TRV II sold 164,996 shares of Common Stock of the Issuer in multiple transactions at prices ranging from $30.10 to $30.76, inclusive, at a weighted average price per share of $30.23. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (4).

F4 · price: On June 4, 2021, TRV II sold 164,996 shares of Common Stock of the Issuer in multiple transactions at prices ranging from $30.10 to $30.76, inclusive, at a weighted average price per share of $30.23. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (4).

F5 · balance_after: After the above transaction, TRV II owned 0 shares of Common Stock of the Issuer.

F3 · ownership.nature: The Reporting Person is a partner of each of Third Rock Ventures GP II, L.P., TRV GP III, L.P. and Third Rock Ventures GP IV, L.P. which is the general partner of each of TRV II, Third Rock Ventures III, L.P. ("TRV III") and Third Rock Ventures IV, L.P. ("TRV IV" and collectively with TRV II and TRV III, "the Funds"), respectively. The Reporting Person disclaims beneficial ownership over the shares held by the Funds, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0000899243-21-022346 · doc4.xml · nonDerivative · entry 1

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnote

Disclosed balance after: 0

F1 · shares: On June 3, 2021, Third Rock Ventures II, L.P. ("TRV II") sold 378,117 shares of Common Stock of the Issuer in multiple transactions at prices ranging from $30.00 to $30.50, inclusive, at a weighted average price per share of $30.20. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (1).

F1 · price: On June 3, 2021, Third Rock Ventures II, L.P. ("TRV II") sold 378,117 shares of Common Stock of the Issuer in multiple transactions at prices ranging from $30.00 to $30.50, inclusive, at a weighted average price per share of $30.20. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (1).

F2 · balance_after: After the above transaction, TRV II owned 164,996 shares of Common Stock of the Issuer.

F3 · ownership.nature: The Reporting Person is a partner of each of Third Rock Ventures GP II, L.P., TRV GP III, L.P. and Third Rock Ventures GP IV, L.P. which is the general partner of each of TRV II, Third Rock Ventures III, L.P. ("TRV III") and Third Rock Ventures IV, L.P. ("TRV IV" and collectively with TRV II and TRV III, "the Funds"), respectively. The Reporting Person disclaims beneficial ownership over the shares held by the Funds, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0000899243-21-020884 · doc4.xml · nonDerivative · entry 2

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 0

F4 · shares: On May 26, 2021, TRV II sold 1,231,204 shares of Common Stock of the Issuer in multiple transactions at prices ranging from $30.50 to $31.14, inclusive, at a weighted average price per share of $30.53. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (4).

F4 · price: On May 26, 2021, TRV II sold 1,231,204 shares of Common Stock of the Issuer in multiple transactions at prices ranging from $30.50 to $31.14, inclusive, at a weighted average price per share of $30.53. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (4).

F5 · balance_after: After the above transaction, TRV II owned 543,113 shares of Common Stock of the Issuer.

F3 · ownership.nature: The Reporting Person is a partner of each of Third Rock Ventures GP II, L.P., TRV GP III, L.P. and Third Rock Ventures GP IV, L.P. which is the general partner of each of TRV II, Third Rock Ventures III, L.P. ("TRV III") and Third Rock Ventures IV, L.P. ("TRV IV" and collectively with TRV II and TRV III, "the Funds"), respectively. The Reporting Person disclaims beneficial ownership over the shares held by the Funds, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0000899243-21-020884 · doc4.xml · nonDerivative · entry 1

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnotes

Disclosed balance after: 0

F1 · shares: On May 25, 2021, Third Rock Ventures II, L.P. ("TRV II") sold 135,000 shares of Common Stock of the Issuer in multiple transactions at prices ranging from $30.85 to $31.25, inclusive, at a weighted average price per share of $30.93. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (1).

F1 · price: On May 25, 2021, Third Rock Ventures II, L.P. ("TRV II") sold 135,000 shares of Common Stock of the Issuer in multiple transactions at prices ranging from $30.85 to $31.25, inclusive, at a weighted average price per share of $30.93. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (1).

F2 · balance_after: After the above transaction, TRV II owned 1,774,317 shares of Common Stock of the Issuer.

F3 · ownership.nature: The Reporting Person is a partner of each of Third Rock Ventures GP II, L.P., TRV GP III, L.P. and Third Rock Ventures GP IV, L.P. which is the general partner of each of TRV II, Third Rock Ventures III, L.P. ("TRV III") and Third Rock Ventures IV, L.P. ("TRV IV" and collectively with TRV II and TRV III, "the Funds"), respectively. The Reporting Person disclaims beneficial ownership over the shares held by the Funds, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0000899243-21-008467 · doc4.xml · nonDerivative · entry 1

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnote

Disclosed balance after: 0

F1 · kind: On February 24, 2020, Third Rock Ventures III, L.P. ("TRV III") distributed for no consideration 1,500,000 shares of Common Stock of the Issuer (the "Shares") to its limited partners and to Third Rock Ventures GP III, L.P. ("TRV GP III"), the general partner of TRV III, representing each such partner's pro rata interest in such Shares. On the same date, TRV GP III distributed, for no consideration, the Shares it received in the distribution by TRV III to its partners, representing each such partner's pro rata interest in such Shares. All of the aforementioned distributions were made in accordance with the exemptions afforded by Rules 16a-13 and 16a-9 of the Securities Exchange Act of 1934, as amended. After such distribution, TRV III directly held 5,524,031 shares of Common Stock of the Issuer.

F1 · shares: On February 24, 2020, Third Rock Ventures III, L.P. ("TRV III") distributed for no consideration 1,500,000 shares of Common Stock of the Issuer (the "Shares") to its limited partners and to Third Rock Ventures GP III, L.P. ("TRV GP III"), the general partner of TRV III, representing each such partner's pro rata interest in such Shares. On the same date, TRV GP III distributed, for no consideration, the Shares it received in the distribution by TRV III to its partners, representing each such partner's pro rata interest in such Shares. All of the aforementioned distributions were made in accordance with the exemptions afforded by Rules 16a-13 and 16a-9 of the Securities Exchange Act of 1934, as amended. After such distribution, TRV III directly held 5,524,031 shares of Common Stock of the Issuer.

F1 · price: On February 24, 2020, Third Rock Ventures III, L.P. ("TRV III") distributed for no consideration 1,500,000 shares of Common Stock of the Issuer (the "Shares") to its limited partners and to Third Rock Ventures GP III, L.P. ("TRV GP III"), the general partner of TRV III, representing each such partner's pro rata interest in such Shares. On the same date, TRV GP III distributed, for no consideration, the Shares it received in the distribution by TRV III to its partners, representing each such partner's pro rata interest in such Shares. All of the aforementioned distributions were made in accordance with the exemptions afforded by Rules 16a-13 and 16a-9 of the Securities Exchange Act of 1934, as amended. After such distribution, TRV III directly held 5,524,031 shares of Common Stock of the Issuer.

F1 · balance_after: On February 24, 2020, Third Rock Ventures III, L.P. ("TRV III") distributed for no consideration 1,500,000 shares of Common Stock of the Issuer (the "Shares") to its limited partners and to Third Rock Ventures GP III, L.P. ("TRV GP III"), the general partner of TRV III, representing each such partner's pro rata interest in such Shares. On the same date, TRV GP III distributed, for no consideration, the Shares it received in the distribution by TRV III to its partners, representing each such partner's pro rata interest in such Shares. All of the aforementioned distributions were made in accordance with the exemptions afforded by Rules 16a-13 and 16a-9 of the Securities Exchange Act of 1934, as amended. After such distribution, TRV III directly held 5,524,031 shares of Common Stock of the Issuer.

F2 · ownership.nature: The Reporting Person is a partner of each of Third Rock Ventures GP II, L.P., TRV GP III and Third Rock Ventures GP IV, L.P. which is the general partner of each of Third Rock Ventures II, L.P. ("TRV II"), TRV III and Third Rock Ventures IV, L.P. ("TRV IV" and collectively with TRV II and TRV III, "the Funds"), respectively. The Reporting Person disclaims beneficial ownership over the shares held by the Funds, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0000899243-21-007436 · doc4.xml · derivative · entry 6

Exter Neil · CIK 0001620014 · Director · 10% owner

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnote

Disclosed balance after: 0

Underlying: Common Stock · 54,642 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F3 · derivative.exercise_price: On February 17, 2021, the Series D Preferred Stock automatically converted into Common Stock on a 5.3-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date.

F3 · derivative.exercise_date: On February 17, 2021, the Series D Preferred Stock automatically converted into Common Stock on a 5.3-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date.

F3 · derivative.expiration_date: On February 17, 2021, the Series D Preferred Stock automatically converted into Common Stock on a 5.3-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date.

F4 · ownership.nature: Held of record by Third Rock Ventures III, L.P. ("TRV III"). The Reporting Person is a partner of Third Rock Ventures GP III, L.P., which is the general partner of TRV III. The Reporting Person disclaims beneficial ownership over such shares, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0000899243-21-007436 · doc4.xml · derivative · entry 5

Exter Neil · CIK 0001620014 · Director · 10% owner

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnote

Disclosed balance after: 0

Underlying: Common Stock · 98,929 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: On February 17, 2021, the Series C Preferred Stock automatically converted into Common Stock on a 12.6352-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date.

F2 · derivative.exercise_date: On February 17, 2021, the Series C Preferred Stock automatically converted into Common Stock on a 12.6352-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date.

F2 · derivative.expiration_date: On February 17, 2021, the Series C Preferred Stock automatically converted into Common Stock on a 12.6352-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date.

F4 · ownership.nature: Held of record by Third Rock Ventures III, L.P. ("TRV III"). The Reporting Person is a partner of Third Rock Ventures GP III, L.P., which is the general partner of TRV III. The Reporting Person disclaims beneficial ownership over such shares, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0000899243-21-007436 · doc4.xml · derivative · entry 4

Exter Neil · CIK 0001620014 · Director · 10% owner

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnote

Disclosed balance after: 0

Underlying: Common Stock · 2,938,945 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · derivative.exercise_price: On February 17, 2021, the Series A Preferred Stock automatically converted into Common Stock on a 15.529-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date.

F1 · derivative.exercise_date: On February 17, 2021, the Series A Preferred Stock automatically converted into Common Stock on a 15.529-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date.

F1 · derivative.expiration_date: On February 17, 2021, the Series A Preferred Stock automatically converted into Common Stock on a 15.529-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date.

F4 · ownership.nature: Held of record by Third Rock Ventures III, L.P. ("TRV III"). The Reporting Person is a partner of Third Rock Ventures GP III, L.P., which is the general partner of TRV III. The Reporting Person disclaims beneficial ownership over such shares, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0000899243-21-007436 · doc4.xml · nonDerivative · entry 3

Exter Neil · CIK 0001620014 · Director · 10% owner

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnote

Disclosed balance after: 3,139,685

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F3 · price: On February 17, 2021, the Series D Preferred Stock automatically converted into Common Stock on a 5.3-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date.

F4 · ownership.nature: Held of record by Third Rock Ventures III, L.P. ("TRV III"). The Reporting Person is a partner of Third Rock Ventures GP III, L.P., which is the general partner of TRV III. The Reporting Person disclaims beneficial ownership over such shares, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0000899243-21-007436 · doc4.xml · nonDerivative · entry 2

Exter Neil · CIK 0001620014 · Director · 10% owner

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnote

Disclosed balance after: 3,085,043

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · price: On February 17, 2021, the Series C Preferred Stock automatically converted into Common Stock on a 12.6352-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date.

F4 · ownership.nature: Held of record by Third Rock Ventures III, L.P. ("TRV III"). The Reporting Person is a partner of Third Rock Ventures GP III, L.P., which is the general partner of TRV III. The Reporting Person disclaims beneficial ownership over such shares, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0000899243-21-007436 · doc4.xml · nonDerivative · entry 1

Exter Neil · CIK 0001620014 · Director · 10% owner

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnote

Disclosed balance after: 2,986,114

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · price: On February 17, 2021, the Series A Preferred Stock automatically converted into Common Stock on a 15.529-for-one basis without payment of further consideration upon closing of the initial public offering of the Issuer's common stock. The shares had no expiration date.

F4 · ownership.nature: Held of record by Third Rock Ventures III, L.P. ("TRV III"). The Reporting Person is a partner of Third Rock Ventures GP III, L.P., which is the general partner of TRV III. The Reporting Person disclaims beneficial ownership over such shares, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0000899243-21-006693 · doc4.xml · derivative · entry 1

Exter Neil · CIK 0001620014 · Director · 10% owner

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 20,000

Underlying: Common Stock · 20,000 shares

Expires 2031-02-10

F1 · derivative.exercise_date: The option was granted on February 11, 2021 for 20,000 shares. The shares underlying the option vest in equal monthly installments until the third anniversary of the grant date, subject to the reporting person's continued service.

SEC source: 0000899243-20-032782 · doc4.xml · nonDerivative · entry 1

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnote

Disclosed balance after: 0

F1 · kind: On December 2, 2020, Third Rock Ventures III, L.P. ("TRV III") distributed for no consideration 1,000,000 shares of Common Stock of the Issuer (the "Shares") to its limited partners and to Third Rock Ventures GP III, L.P. ("TRV GP II"), the general partner of TRV III, representing each such partner's pro rata interest in such Shares. On the same date, TRV GP III distributed, for no consideration, the Shares it received in the distribution by TRV III to its partners, representing each such partner's pro rata interest in such Shares. All of the aforementioned distributions were made in accordance with the exemptions afforded by Rules 16a-13 and 16a-9 of the Securities Exchange Act of 1934, as amended. After such distribution, TRV III directly held 7,024,031 shares of Common Stock of the Issuer.

F1 · shares: On December 2, 2020, Third Rock Ventures III, L.P. ("TRV III") distributed for no consideration 1,000,000 shares of Common Stock of the Issuer (the "Shares") to its limited partners and to Third Rock Ventures GP III, L.P. ("TRV GP II"), the general partner of TRV III, representing each such partner's pro rata interest in such Shares. On the same date, TRV GP III distributed, for no consideration, the Shares it received in the distribution by TRV III to its partners, representing each such partner's pro rata interest in such Shares. All of the aforementioned distributions were made in accordance with the exemptions afforded by Rules 16a-13 and 16a-9 of the Securities Exchange Act of 1934, as amended. After such distribution, TRV III directly held 7,024,031 shares of Common Stock of the Issuer.

F1 · price: On December 2, 2020, Third Rock Ventures III, L.P. ("TRV III") distributed for no consideration 1,000,000 shares of Common Stock of the Issuer (the "Shares") to its limited partners and to Third Rock Ventures GP III, L.P. ("TRV GP II"), the general partner of TRV III, representing each such partner's pro rata interest in such Shares. On the same date, TRV GP III distributed, for no consideration, the Shares it received in the distribution by TRV III to its partners, representing each such partner's pro rata interest in such Shares. All of the aforementioned distributions were made in accordance with the exemptions afforded by Rules 16a-13 and 16a-9 of the Securities Exchange Act of 1934, as amended. After such distribution, TRV III directly held 7,024,031 shares of Common Stock of the Issuer.

F1 · balance_after: On December 2, 2020, Third Rock Ventures III, L.P. ("TRV III") distributed for no consideration 1,000,000 shares of Common Stock of the Issuer (the "Shares") to its limited partners and to Third Rock Ventures GP III, L.P. ("TRV GP II"), the general partner of TRV III, representing each such partner's pro rata interest in such Shares. On the same date, TRV GP III distributed, for no consideration, the Shares it received in the distribution by TRV III to its partners, representing each such partner's pro rata interest in such Shares. All of the aforementioned distributions were made in accordance with the exemptions afforded by Rules 16a-13 and 16a-9 of the Securities Exchange Act of 1934, as amended. After such distribution, TRV III directly held 7,024,031 shares of Common Stock of the Issuer.

F2 · ownership.nature: The Reporting Person is a partner of each of Third Rock Ventures GP II, L.P., TRV GP III and Third Rock Ventures GP IV, L.P. which is the general partner of each of Third Rock Ventures II, L.P. ("TRV II"), TRV III and Third Rock Ventures IV, L.P. ("TRV IV" and collectively with TRV II and TRV III, "the Funds"), respectively. The Reporting Person disclaims beneficial ownership over the shares held by the Funds, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0000899243-20-024899 · doc4.xml · nonDerivative · entry 1

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnote

Disclosed balance after: 0

F1 · kind: On September 9, 2020, Third Rock Ventures III, L.P. ("TRV III") distributed, for no consideration, 1,000,000 shares of Common Stock of the Issuer (the "Shares") to its limited partners and to Third Rock Ventures GP III, L.P. ("TRV GP III"), the general partner of TRV III, representing each such partner's pro rata interest in such Shares. On the same date, TRV GP III distributed, for no consideration, the Shares it received in the distribution by TRV III to its partners, representing each such partner's pro rata interest in such Shares. All of the aforementioned distributions were made in accordance with the exemptions afforded by Rules 16a-13 and 16a-9 of the Securities Exchange Act of 1934, as amended. After such distribution, TRV III directly held 8,024,031 shares of Common Stock of the Issuer.

F1 · shares: On September 9, 2020, Third Rock Ventures III, L.P. ("TRV III") distributed, for no consideration, 1,000,000 shares of Common Stock of the Issuer (the "Shares") to its limited partners and to Third Rock Ventures GP III, L.P. ("TRV GP III"), the general partner of TRV III, representing each such partner's pro rata interest in such Shares. On the same date, TRV GP III distributed, for no consideration, the Shares it received in the distribution by TRV III to its partners, representing each such partner's pro rata interest in such Shares. All of the aforementioned distributions were made in accordance with the exemptions afforded by Rules 16a-13 and 16a-9 of the Securities Exchange Act of 1934, as amended. After such distribution, TRV III directly held 8,024,031 shares of Common Stock of the Issuer.

F1 · price: On September 9, 2020, Third Rock Ventures III, L.P. ("TRV III") distributed, for no consideration, 1,000,000 shares of Common Stock of the Issuer (the "Shares") to its limited partners and to Third Rock Ventures GP III, L.P. ("TRV GP III"), the general partner of TRV III, representing each such partner's pro rata interest in such Shares. On the same date, TRV GP III distributed, for no consideration, the Shares it received in the distribution by TRV III to its partners, representing each such partner's pro rata interest in such Shares. All of the aforementioned distributions were made in accordance with the exemptions afforded by Rules 16a-13 and 16a-9 of the Securities Exchange Act of 1934, as amended. After such distribution, TRV III directly held 8,024,031 shares of Common Stock of the Issuer.

F1 · balance_after: On September 9, 2020, Third Rock Ventures III, L.P. ("TRV III") distributed, for no consideration, 1,000,000 shares of Common Stock of the Issuer (the "Shares") to its limited partners and to Third Rock Ventures GP III, L.P. ("TRV GP III"), the general partner of TRV III, representing each such partner's pro rata interest in such Shares. On the same date, TRV GP III distributed, for no consideration, the Shares it received in the distribution by TRV III to its partners, representing each such partner's pro rata interest in such Shares. All of the aforementioned distributions were made in accordance with the exemptions afforded by Rules 16a-13 and 16a-9 of the Securities Exchange Act of 1934, as amended. After such distribution, TRV III directly held 8,024,031 shares of Common Stock of the Issuer.

F2 · ownership.nature: The Reporting Person is a partner of each of Third Rock Ventures GP II, L.P., TRV GP III and Third Rock Ventures GP IV, L.P. which is the general partner of each of Third Rock Ventures II, L.P. ("TRV II"), TRV III and Third Rock Ventures IV, L.P. ("TRV IV" and collectively with TRV II and TRV III, "the Funds"), respectively. The Reporting Person disclaims beneficial ownership over the shares held by the Funds, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0000899243-20-015873 · doc4.xml · derivative · entry 3

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnote

Disclosed balance after: 0

Underlying: Common Stock · 0 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F6 · derivative.exercise_price: The Series A Preferred Stock converted into Common Stock on a 7.15-for-one basis upon the closing of the Issuer's initial public offering without payment of consideration. The Series A Preferred Stock was convertible at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering. The Series A Preferred Stock had no expiration date.

F7 · shares: Prior to the conversion, TRV III directly held 39,750,000 shares of the Issuer's Series A Preferred Stock and TRV IV directly held 15,250,000 shares of the Issuer's Series A Preferred Stock.

F6 · derivative.exercise_date: The Series A Preferred Stock converted into Common Stock on a 7.15-for-one basis upon the closing of the Issuer's initial public offering without payment of consideration. The Series A Preferred Stock was convertible at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering. The Series A Preferred Stock had no expiration date.

F6 · derivative.expiration_date: The Series A Preferred Stock converted into Common Stock on a 7.15-for-one basis upon the closing of the Issuer's initial public offering without payment of consideration. The Series A Preferred Stock was convertible at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering. The Series A Preferred Stock had no expiration date.

F1 · derivative.underlying_shares: Third Rock Ventures III ("TRV III") received 5,559,440 shares of the Issuer's Common Stock and Third Rock Ventures IV, L.P. ("TRV IV") received 2,132,867 shares of the Issuer's Common Stock, in each case issued upon conversion of the Series A Preferred Stock of the Issuer in connection with the closing of the Issuer's initial public offering.

F3 · ownership.nature: The Reporting Person is a partner of each of Third Rock Ventures GP III, L.P. and Third Rock Ventures GP IV, L.P. which is the ultimate general partner of each of TRV III and TRV IV ("the Funds"), respectively. The Reporting Person disclaims beneficial ownership over the shares held by the Funds, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0000899243-20-015873 · doc4.xml · nonDerivative · entry 1

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnote

Disclosed balance after: 0

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · shares: Third Rock Ventures III ("TRV III") received 5,559,440 shares of the Issuer's Common Stock and Third Rock Ventures IV, L.P. ("TRV IV") received 2,132,867 shares of the Issuer's Common Stock, in each case issued upon conversion of the Series A Preferred Stock of the Issuer in connection with the closing of the Issuer's initial public offering.

F2 · price: After the reported transaction, TRV III directly holds 5,839,160 shares of the Issuer's Common Stock and TRV IV directly holds 2,132,867 shares of the Issuer's Common Stock.

F2 · balance_after: After the reported transaction, TRV III directly holds 5,839,160 shares of the Issuer's Common Stock and TRV IV directly holds 2,132,867 shares of the Issuer's Common Stock.

F3 · ownership.nature: The Reporting Person is a partner of each of Third Rock Ventures GP III, L.P. and Third Rock Ventures GP IV, L.P. which is the ultimate general partner of each of TRV III and TRV IV ("the Funds"), respectively. The Reporting Person disclaims beneficial ownership over the shares held by the Funds, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0000899243-20-015873 · doc4.xml · derivative · entry 2

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 26,573

Underlying: Common Stock · 26,573 shares

Expires 2030-03-30

F4 · derivative.exercise_price: On May 22, 2020, the Issuer completed a one-for-7.15 reverse stock split of the Issuer's Common Stock. This amount has been adjusted to reflect this reverse stock split.

F4 · shares: On May 22, 2020, the Issuer completed a one-for-7.15 reverse stock split of the Issuer's Common Stock. This amount has been adjusted to reflect this reverse stock split.

F5 · derivative.exercise_date: 1/12th of the shares subject to this option vest and become exercisable in substantially equal installments on the last date of each calendar quarter, with the first tranche vesting on June 30, 2020, subject to the Reporting Person's continuous service to the Issuer on each such date.

F4 · derivative.underlying_shares: On May 22, 2020, the Issuer completed a one-for-7.15 reverse stock split of the Issuer's Common Stock. This amount has been adjusted to reflect this reverse stock split.

F4 · balance_after: On May 22, 2020, the Issuer completed a one-for-7.15 reverse stock split of the Issuer's Common Stock. This amount has been adjusted to reflect this reverse stock split.

SEC source: 0001567619-20-004504 · doc1.xml · derivative · entry 4

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnote

Disclosed balance after: 0

Underlying: Common Stock · 0 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F6 · derivative.exercise_price: The Series C Convertible Preferred Stock automatically converted into shares of Common Stock on a 1:1 basis immediately prior to the completion of the Issuer's initial public offering of Common Stock and has no expiration date.

F1 · shares: Reflects a 1-for-4.8661 reverse stock split of the Issuer's outstanding securities effected prior to the effectiveness of the Issuer's S-1 Registration Statement.

F10 · shares: Prior to the conversion, TRV III directly held 49,879 shares of the Series C Preferred on an as converted to common stock basis. TRV IV directly held 49,879 shares of shares of the Issuer's Series C Preferred on an as converted to common stock basis. The Reporting Person is a partner of each of Third Rock Ventures GP III, L.P. and Third Rock Ventures GP IV, L.P., which is the general partner of each of TRV III and TRV IV, respectively. The Reporting Person disclaims beneficial ownership over such shares, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

F6 · derivative.exercise_date: The Series C Convertible Preferred Stock automatically converted into shares of Common Stock on a 1:1 basis immediately prior to the completion of the Issuer's initial public offering of Common Stock and has no expiration date.

F6 · derivative.expiration_date: The Series C Convertible Preferred Stock automatically converted into shares of Common Stock on a 1:1 basis immediately prior to the completion of the Issuer's initial public offering of Common Stock and has no expiration date.

F1 · derivative.underlying_shares: Reflects a 1-for-4.8661 reverse stock split of the Issuer's outstanding securities effected prior to the effectiveness of the Issuer's S-1 Registration Statement.

F7 · ownership.nature: The Reporting Person is a partner of each of Third Rock Ventures GP II, L.P., Third Rock Ventures GP III, L.P. and Third Rock Ventures GP IV, L.P. which is the general partner of each of TRV II, TRV III and TRV IV ("the Funds"), respectively. The Reporting Person disclaims beneficial ownership over the shares held by the Funds, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

F10 · ownership.nature: Prior to the conversion, TRV III directly held 49,879 shares of the Series C Preferred on an as converted to common stock basis. TRV IV directly held 49,879 shares of shares of the Issuer's Series C Preferred on an as converted to common stock basis. The Reporting Person is a partner of each of Third Rock Ventures GP III, L.P. and Third Rock Ventures GP IV, L.P., which is the general partner of each of TRV III and TRV IV, respectively. The Reporting Person disclaims beneficial ownership over such shares, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0001567619-20-004504 · doc1.xml · derivative · entry 3

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnote

Disclosed balance after: 0

Underlying: Common Stock · 0 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F5 · derivative.exercise_price: The Series B Convertible Preferred Stock automatically converted into shares of Common Stock on a 1:1 basis immediately prior to the completion of the Issuer's initial public offering of Common Stock and has no expiration date.

F1 · shares: Reflects a 1-for-4.8661 reverse stock split of the Issuer's outstanding securities effected prior to the effectiveness of the Issuer's S-1 Registration Statement.

F9 · shares: Prior to the conversion, TRV III directly held 342,505 shares of the Series B Preferred on an as converted to common stock basis. TRV II directly held 1,909,317 shares of the Issuer's Series B Preferred on an as converted to common stock basis. TRV IV directly held 342,505 shares of the Issuer's Series B Preferred on an as converted to common stock basis. The Reporting Person is a partner of each of Third Rock Ventures GP II, L.P., Third Rock Ventures GP III, L.P. and Third Rock Ventures GP IV, L.P. which is the general partner of each of TRV II, TRV III and TRV IV, respectively. The Reporting Person disclaims beneficial ownership over such shares, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

F5 · derivative.exercise_date: The Series B Convertible Preferred Stock automatically converted into shares of Common Stock on a 1:1 basis immediately prior to the completion of the Issuer's initial public offering of Common Stock and has no expiration date.

F5 · derivative.expiration_date: The Series B Convertible Preferred Stock automatically converted into shares of Common Stock on a 1:1 basis immediately prior to the completion of the Issuer's initial public offering of Common Stock and has no expiration date.

F1 · derivative.underlying_shares: Reflects a 1-for-4.8661 reverse stock split of the Issuer's outstanding securities effected prior to the effectiveness of the Issuer's S-1 Registration Statement.

F7 · ownership.nature: The Reporting Person is a partner of each of Third Rock Ventures GP II, L.P., Third Rock Ventures GP III, L.P. and Third Rock Ventures GP IV, L.P. which is the general partner of each of TRV II, TRV III and TRV IV ("the Funds"), respectively. The Reporting Person disclaims beneficial ownership over the shares held by the Funds, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

F9 · ownership.nature: Prior to the conversion, TRV III directly held 342,505 shares of the Series B Preferred on an as converted to common stock basis. TRV II directly held 1,909,317 shares of the Issuer's Series B Preferred on an as converted to common stock basis. TRV IV directly held 342,505 shares of the Issuer's Series B Preferred on an as converted to common stock basis. The Reporting Person is a partner of each of Third Rock Ventures GP II, L.P., Third Rock Ventures GP III, L.P. and Third Rock Ventures GP IV, L.P. which is the general partner of each of TRV II, TRV III and TRV IV, respectively. The Reporting Person disclaims beneficial ownership over such shares, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0001567619-20-004504 · doc1.xml · derivative · entry 2

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnote

Disclosed balance after: 0

Underlying: Common Stock · 0 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F4 · derivative.exercise_price: The Series A Convertible Preferred Stock automatically converted into shares of Common Stock on a 1:1 basis immediately prior to the completion of the Issuer's initial public offering of Common Stock and has no expiration date.

F1 · shares: Reflects a 1-for-4.8661 reverse stock split of the Issuer's outstanding securities effected prior to the effectiveness of the Issuer's S-1 Registration Statement.

F8 · shares: Prior to the conversion, TRV III directly held 8,220,641 shares of the Series A Preferred on an as converted to common stock basis. TRV IV directly held 1,027,516 shares of the Issuer's Series A Preferred on an as converted to common stock basis. The Reporting Person is a partner of each of Third Rock Ventures GP III, L.P. and Third Rock Ventures GP IV, L.P., which is the general partner of each of TRV III and TRV IV, respectively. The Reporting Person disclaims beneficial ownership over such shares, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

F4 · derivative.exercise_date: The Series A Convertible Preferred Stock automatically converted into shares of Common Stock on a 1:1 basis immediately prior to the completion of the Issuer's initial public offering of Common Stock and has no expiration date.

F4 · derivative.expiration_date: The Series A Convertible Preferred Stock automatically converted into shares of Common Stock on a 1:1 basis immediately prior to the completion of the Issuer's initial public offering of Common Stock and has no expiration date.

F1 · derivative.underlying_shares: Reflects a 1-for-4.8661 reverse stock split of the Issuer's outstanding securities effected prior to the effectiveness of the Issuer's S-1 Registration Statement.

F7 · ownership.nature: The Reporting Person is a partner of each of Third Rock Ventures GP II, L.P., Third Rock Ventures GP III, L.P. and Third Rock Ventures GP IV, L.P. which is the general partner of each of TRV II, TRV III and TRV IV ("the Funds"), respectively. The Reporting Person disclaims beneficial ownership over the shares held by the Funds, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

F8 · ownership.nature: Prior to the conversion, TRV III directly held 8,220,641 shares of the Series A Preferred on an as converted to common stock basis. TRV IV directly held 1,027,516 shares of the Issuer's Series A Preferred on an as converted to common stock basis. The Reporting Person is a partner of each of Third Rock Ventures GP III, L.P. and Third Rock Ventures GP IV, L.P., which is the general partner of each of TRV III and TRV IV, respectively. The Reporting Person disclaims beneficial ownership over such shares, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0001567619-20-004504 · doc1.xml · nonDerivative · entry 1

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnote

Disclosed balance after: 0

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · shares: Reflects a 1-for-4.8661 reverse stock split of the Issuer's outstanding securities effected prior to the effectiveness of the Issuer's S-1 Registration Statement.

F2 · shares: Third Rock Ventures II ("TRV II") directly holds 1,909,317 shares of the Issuer's common stock, Third Rock Ventures III, L.P. ("TRV III") directly holds 8,613,025 shares of the Issuer's common stock and Third Rock Ventures IV, L.P. ("TRV IV") directly holds 1,419,900 shares of the Issuer's common stock upon the conversion of the Issuer's Series A convertible preferred stock (the "Series A Preferred"), the Issuer's Series B convertible preferred stock (the "Series B Preferred"), and the Issuer's Series C convertible preferred stock (the "Series C Preferred"). The Reporting Person disclaims beneficial ownership over such shares, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

F1 · balance_after: Reflects a 1-for-4.8661 reverse stock split of the Issuer's outstanding securities effected prior to the effectiveness of the Issuer's S-1 Registration Statement.

F3 · balance_after: TRV II directly holds 1,909,317 shares, TRV III directly holds 9,024,031 shares and TRV IV directly holds 1,419,900 shares. The Reporting Person disclaims beneficial ownership over such shares, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

F7 · ownership.nature: The Reporting Person is a partner of each of Third Rock Ventures GP II, L.P., Third Rock Ventures GP III, L.P. and Third Rock Ventures GP IV, L.P. which is the general partner of each of TRV II, TRV III and TRV IV ("the Funds"), respectively. The Reporting Person disclaims beneficial ownership over the shares held by the Funds, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0001567619-20-004015 · doc1.xml · derivative · entry 1

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 36,168

Underlying: Common Stock · 36,168 shares

Expires 2030-02-11

F1 · derivative.exercise_date: The option becomes exercisable as it vests and the shares subject to the option vest with respect to 1/36 of the shares subject thereto on each monthly anniversary of February 12, 2020, subject to the Reporting Person's continued employment or service relationship with the Issuer on each such vesting date.

SEC source: 0001104659-18-039180 · a4.xml · derivative · entry 1

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 10,000

Underlying: Common Stock · 10,000 shares

Expires 2028-06-05

F1 · derivative.exercise_date: The options fully vest upon the earlier of (i) 1 year from the date of grant or (ii) the date of the Issuer's next annual meeting of the stockholders.

SEC source: 0001104659-17-061969 · a4.xml · derivative · entry 3

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

Underlying: Common Stock · 0 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: Each share of the Series A Preferred and Series A-1 Preferred converted into shares of the Issuer's common stock on a 9.17-for-one basis upon the closing of the IPO without payment or consideration. The Series A Preferred and Series A-1 Preferred were convertible at any time at the holder's election and automatically upon the closing of the IPO and had no expiration date.

F5 · shares: Prior to the conversion, the Fund held 9,479,502 and 26,868,642 shares of the Series A Preferred and Series A-1 Preferred, respectively.

F2 · derivative.exercise_date: Each share of the Series A Preferred and Series A-1 Preferred converted into shares of the Issuer's common stock on a 9.17-for-one basis upon the closing of the IPO without payment or consideration. The Series A Preferred and Series A-1 Preferred were convertible at any time at the holder's election and automatically upon the closing of the IPO and had no expiration date.

F2 · derivative.expiration_date: Each share of the Series A Preferred and Series A-1 Preferred converted into shares of the Issuer's common stock on a 9.17-for-one basis upon the closing of the IPO without payment or consideration. The Series A Preferred and Series A-1 Preferred were convertible at any time at the holder's election and automatically upon the closing of the IPO and had no expiration date.

F6 · derivative.underlying_shares: Prior to the conversion, the Fund held 1,033,751 and 2,930,059 shares of the Series A Preferred and Series A-1 Preferred, respectively, on an as converted to common stock basis.

F4 · ownership.nature: The Reporting Person is a partner of Third Rock Ventures GP, L.P., which is the general partner of the Fund. The Reporting Person disclaims beneficial ownership over the shares held by the Fund, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

F6 · ownership.nature: Prior to the conversion, the Fund held 1,033,751 and 2,930,059 shares of the Series A Preferred and Series A-1 Preferred, respectively, on an as converted to common stock basis.

SEC source: 0001104659-17-061969 · a4.xml · derivative · entry 2

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

Underlying: Common Stock · 0 shares

Expires not disclosed

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F2 · derivative.exercise_price: Each share of the Series A Preferred and Series A-1 Preferred converted into shares of the Issuer's common stock on a 9.17-for-one basis upon the closing of the IPO without payment or consideration. The Series A Preferred and Series A-1 Preferred were convertible at any time at the holder's election and automatically upon the closing of the IPO and had no expiration date.

F5 · shares: Prior to the conversion, the Fund held 9,479,502 and 26,868,642 shares of the Series A Preferred and Series A-1 Preferred, respectively.

F2 · derivative.exercise_date: Each share of the Series A Preferred and Series A-1 Preferred converted into shares of the Issuer's common stock on a 9.17-for-one basis upon the closing of the IPO without payment or consideration. The Series A Preferred and Series A-1 Preferred were convertible at any time at the holder's election and automatically upon the closing of the IPO and had no expiration date.

F2 · derivative.expiration_date: Each share of the Series A Preferred and Series A-1 Preferred converted into shares of the Issuer's common stock on a 9.17-for-one basis upon the closing of the IPO without payment or consideration. The Series A Preferred and Series A-1 Preferred were convertible at any time at the holder's election and automatically upon the closing of the IPO and had no expiration date.

F6 · derivative.underlying_shares: Prior to the conversion, the Fund held 1,033,751 and 2,930,059 shares of the Series A Preferred and Series A-1 Preferred, respectively, on an as converted to common stock basis.

F4 · ownership.nature: The Reporting Person is a partner of Third Rock Ventures GP, L.P., which is the general partner of the Fund. The Reporting Person disclaims beneficial ownership over the shares held by the Fund, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

F6 · ownership.nature: Prior to the conversion, the Fund held 1,033,751 and 2,930,059 shares of the Series A Preferred and Series A-1 Preferred, respectively, on an as converted to common stock basis.

SEC source: 0001104659-17-061969 · a4.xml · nonDerivative · entry 1

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See Footnotes

Disclosed balance after: 0

Exercise/conversion can include RSU settlement. Transaction price and option strike are different fields; a missing price is not zero. Derivative and underlying rows can describe the same event.

F1 · shares: Represents 3,963,810 shares of the Issuer's common stock held by Third Rock Ventures, L.P. (the "Fund") upon conversion of the Issuer's series A convertible preferred stock (the "Series A Preferred") and series A-1 junior preferred stock (the "Series A-1 Preferred") upon closing of the Issuer's initial public offering (the "IPO").

F2 · price: Each share of the Series A Preferred and Series A-1 Preferred converted into shares of the Issuer's common stock on a 9.17-for-one basis upon the closing of the IPO without payment or consideration. The Series A Preferred and Series A-1 Preferred were convertible at any time at the holder's election and automatically upon the closing of the IPO and had no expiration date.

F3 · balance_after: Represents (i) 3,963,810 shares of the Issuer's common stock held by the Fund upon conversion of the Series A Preferred and Series A-1 Preferred upon closing of the IPO and (ii) 17,627 shares of the Issuer's common stock held by the Fund prior to the closing of the IPO.

F3 · ownership.nature: Represents (i) 3,963,810 shares of the Issuer's common stock held by the Fund upon conversion of the Series A Preferred and Series A-1 Preferred upon closing of the IPO and (ii) 17,627 shares of the Issuer's common stock held by the Fund prior to the closing of the IPO.

F4 · ownership.nature: The Reporting Person is a partner of Third Rock Ventures GP, L.P., which is the general partner of the Fund. The Reporting Person disclaims beneficial ownership over the shares held by the Fund, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0001140361-17-025787 · doc1.xml · derivative · entry 1

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 14,000

Underlying: Common Stock · 14,000 shares

Expires 2027-06-19

F1 · derivative.exercise_date: The option vests in full on June 20, 2018 subject to the Reporting Person's continued service to the Issuer through such date.

SEC source: 0000899243-17-008729 · doc4.xml · nonDerivative · entry 2

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnote

Disclosed balance after: 0

F4 · shares: On March 27, 2017, TRV sold 650,000 shares of Common Stock of the Issuer. The shares were sold in multiple transactions at prices ranging from $18.00 to $18.45, inclusive, and at a weighted average price of $18.0003. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (4).

F4 · price: On March 27, 2017, TRV sold 650,000 shares of Common Stock of the Issuer. The shares were sold in multiple transactions at prices ranging from $18.00 to $18.45, inclusive, and at a weighted average price of $18.0003. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote (4).

F5 · balance_after: After the transaction referenced in note (4), TRV owned 5,170,348 shares of Common Stock of the Issuer.

F3 · ownership.nature: The reporting person is a partner of Third Rock Ventures GP, L.P., which is the general partner of TRV. The reporting person disclaims beneficial ownership over the shares held by TRV, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0000899243-17-008729 · doc4.xml · nonDerivative · entry 1

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Indirect · See footnote

Disclosed balance after: 0

F1 · shares: On March 23, 2017, Third Rock Ventures, L.P. ("TRV") sold 1,000,000 shares of Common Stock of the Issuer. The shares were sold in one execution at a price per share of $17.0002.

F1 · price: On March 23, 2017, Third Rock Ventures, L.P. ("TRV") sold 1,000,000 shares of Common Stock of the Issuer. The shares were sold in one execution at a price per share of $17.0002.

F2 · balance_after: After the transaction referenced in note (1), TRV owned 5,820,348 shares of Common Stock of the Issuer.

F3 · ownership.nature: The reporting person is a partner of Third Rock Ventures GP, L.P., which is the general partner of TRV. The reporting person disclaims beneficial ownership over the shares held by TRV, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.

SEC source: 0000899243-16-033011 · doc4.xml · nonDerivative · entry 1

Exter Neil · CIK 0001620014 · Director

10b5-1 filing: Not disclosed

Ownership: Direct

Disclosed balance after: 0

F1 · kind: On November 7, 2016, Third Rock Ventures, L.P. ("TRV") distributed, for no consideration, 1,000,000 shares of Common Stock of the Issuer (the "Shares") to its limited partners and to Third Rock Ventures GP, L.P. ("TRV GP"), the general partner of TRV, representing each such partner's pro rata interest in such Shares. On the same date, TRV GP distributed, for no consideration, the Shares it received in the distribution by TRV to its partners, representing each such partner's pro rata interest in such Shares. All of the aforementioned distributions were made in accordance with the exemptions afforded by Rules 16a-13 and 16a-9 of the Securities Exchange Act of 1934, as amended.

F1 · price: On November 7, 2016, Third Rock Ventures, L.P. ("TRV") distributed, for no consideration, 1,000,000 shares of Common Stock of the Issuer (the "Shares") to its limited partners and to Third Rock Ventures GP, L.P. ("TRV GP"), the general partner of TRV, representing each such partner's pro rata interest in such Shares. On the same date, TRV GP distributed, for no consideration, the Shares it received in the distribution by TRV to its partners, representing each such partner's pro rata interest in such Shares. All of the aforementioned distributions were made in accordance with the exemptions afforded by Rules 16a-13 and 16a-9 of the Securities Exchange Act of 1934, as amended.

F2 · ownership.direct: The reporting person is a partner of TRV GP, which is the general partner of TRV. The reporting person disclaims beneficial ownership over the shares held by TRV, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares.