Transaction Details

Footnotes

On February 24, 2021, the reporting person was granted a performance-based stock unit (PSU) under the 2018 Stock Incentive Plan. The shares subject to the PSU vest based on the achievement of four specified performance measures. The shares reported were issued to the reporting person upon vesting of one-quarter of the shares subject to the PSU based on the issuer publicly reporting the initiation of a Phase 3 clinical study of an RNAi therapeutic in development to treat a prevalent disease, as determined by the People, Culture and Compensation (PC&C) Committee of the Issuer Board of Directors on October 1, 2025. | On March 1, 2024, the reporting person was granted a PSU under the 2018 Stock Incentive Plan. The shares subject to the PSU vest based on the achievement of three specified performance measures. The shares reported were issued to the reporting person upon vesting of thirty (30) percent of the shares subject to the PSU based on the issuer publicly reporting the initiation of a Phase 3 clinical study in a prevalent indication, as determined by the PC&C Committee on October 1, 2025. | Represents shares automatically sold by the Company on behalf of the reporting person pursuant to a mandatory sell-to-cover provision in the award agreement required to cover minimum statutory tax withholding obligations that became due upon the vesting and settlement of tranches of PSUs granted to the reporting person on February 24, 2021 and March 1, 2024. | The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $446.19 to $447.19. The reporting person will provide to the issuer, any security holder of the issuer or the SEC staff, upon request, information regarding the number of shares sold at each price within the range. | The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $447.21 to $448.21. The reporting person will provide to the issuer, any security holder of the issuer or the SEC staff, upon request, information regarding the number of shares sold at each price within the range. | The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $448.25 to $449.24. The reporting person will provide to the issuer, any security holder of the issuer or the SEC staff, upon request, information regarding the number of shares sold at each price within the range. | The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $449.26 to $450.26. The reporting person will provide to the issuer, any security holder of the issuer or the SEC staff, upon request, information regarding the number of shares sold at each price within the range. | The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $450.29 to $451.29. The reporting person will provide to the issuer, any security holder of the issuer or the SEC staff, upon request, information regarding the number of shares sold at each price within the range. | The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $451.31 to $452.31. The reporting person will provide to the issuer, any security holder of the issuer or the SEC staff, upon request, information regarding the number of shares sold at each price within the range. | The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $452.33 to $453.31. The reporting person will provide to the issuer, any security holder of the issuer or the SEC staff, upon request, information regarding the number of shares sold at each price within the range. | The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $453.37 to $454.37. The reporting person will provide to the issuer, any security holder of the issuer or the SEC staff, upon request, information regarding the number of shares sold at each price within the range. | The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $454.38 to $455.34. The reporting person will provide to the issuer, any security holder of the issuer or the SEC staff, upon request, information regarding the number of shares sold at each price within the range. | The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $455.42 to $456.09. The reporting person will provide to the issuer, any security holder of the issuer or the SEC staff, upon request, information regarding the number of shares sold at each price within the range. | This transaction was made pursuant to a Rule 10b5-1(c) trading plan adopted by the Reporting Person on September 11, 2024. | The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $449.37 to $450.31. The reporting person will provide to the issuer, any security holder of the issuer or the SEC staff, upon request, information regarding the number of shares sold at each price within the range. | The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $450.47 to $451.16. The reporting person will provide to the issuer, any security holder of the issuer or the SEC staff, upon request, information regarding the number of shares sold at each price within the range. | The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $451.50 to $452.43. The reporting person will provide to the issuer, any security holder of the issuer or the SEC staff, upon request, information regarding the number of shares sold at each price within the range. | The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $452.94 to $453.75. The reporting person will provide to the issuer, any security holder of the issuer or the SEC staff, upon request, information regarding the number of shares sold at each price within the range. | The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $454.25 to $454.76. The reporting person will provide to the issuer, any security holder of the issuer or the SEC staff, upon request, information regarding the number of shares sold at each price within the range. | Reflects shares of ALNY common stock acquired by the Reporting Person under the issuer 401(k) plan as a result of the issuer 401(k) matching contribution program. | Represents shares held in trust, of which the Reporting Persons spouse is co-trustee. The Reporting Person disclaims beneficial ownership of these shares, and the filing of this report is not an admission that the Reporting Person is the beneficial owner of these securities for purposes of Section 16 or for any other purpose.