[Form 4] Alnylam Pharmaceuticals, Inc. Insider Trading Activity

Rhea-AI Filing Summary

Yvonne Greenstreet, Director and CEO of Alnylam Pharmaceuticals (ALNY), reported a mix of equity activity tied to performance compensation and tax withholding on vested awards. On 08/15/2025 she received 14,252 shares upon vesting of 30% of a performance-based stock unit awarded 03/01/2024 after a clinical milestone determination. Following that vesting, multiple automatic sales occurred on 08/18/2025 to satisfy mandatory sell-to-cover tax withholding, reducing her direct holdings from 63,200 to 56,221 shares. The filing also shows 407 shares held indirectly via a managed account and shares acquired under the company 401(k) matching program.

Positive

• Performance-based PSU vested: 14,252 shares issued upon achievement of a clinical milestone, reflecting compensation tied to operational milestones
• 401(k) match participation: 407 shares held indirectly from the issuer's 401(k) matching program, indicating use of company benefit plans

Negative

• Reduction in direct holdings: Direct beneficial ownership decreased from 63,200 to 56,221 shares following mandatory sell-to-cover sales
• Concentrated sales on one day: Multiple sell transactions on 08/18/2025 at prices from ~$447.53 to $456.00 reduced insider stake

Insights

Corporate Governance Expert

TL;DR: Routine executive vesting and mandatory sell-to-cover sales; governance signal is standard compensation mechanics, not an extraordinary event.

The filing documents the vesting of a performance-based stock unit tranche tied to a clinical milestone, which was approved by the compensation committee on 08/15/2025 and settled as 14,252 shares. The subsequent clustered sales on 08/18/2025 are described as mandatory sell-to-cover transactions to satisfy statutory tax withholding obligations rather than discretionary disposals. Holdings moved from 63,200 to 56,221 shares directly owned, and an additional 407 shares are held indirectly via a managed account. These actions align with common executive equity compensation settlement practices and do not by themselves indicate a change in corporate strategy or confidence.

Securities Analyst

TL;DR: Insufficient impact on valuation; transactions are compensation-related and routine.

The reported sales occurred across multiple price ranges, with reported weighted-average prices noted per tranche (examples: $447.98, $449.92, $452.96, up to $456.00). The filing discloses that sales prices represent weighted averages of multiple transactions and that detailed per-transaction breakdowns are available on request. The net effect was a reduction of direct share ownership by 6,979 shares. For investors, this is an expected tax-driven liquidity event following PSU vesting and not a material change to insider ownership trends absent further context.

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Greenstreet Yvonne

(Last) (First) (Middle)

675 WEST KENDALL STREET

HENRI A. TERMEER SQUARE

(Street)

CAMBRIDGE MA 02142

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
ALNYLAM PHARMACEUTICALS, INC. [ ALNY ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	Chief Executive Officer

3. Date of Earliest Transaction (Month/Day/Year)
08/15/2025

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	08/15/2025		A(1)		14,252	A	$0.0	63,200	D
Common Stock	08/18/2025		S(2)		194	D	$447.98(3)	63,006	D
Common Stock	08/18/2025		S(2)		450	D	$449.92(4)	62,556	D
Common Stock	08/18/2025		S(2)		195	D	$450.92(5)	62,361	D
Common Stock	08/18/2025		S(2)		514	D	$451.99(6)	61,847	D
Common Stock	08/18/2025		S(2)		1,646	D	$452.96(7)	60,201	D
Common Stock	08/18/2025		S(2)		2,716	D	$454.04(8)	57,485	D
Common Stock	08/18/2025		S(2)		1,204	D	$454.84(9)	56,281	D
Common Stock	08/18/2025		S(2)		60	D	$455.82(10)	56,221	D
Common Stock								407	I	by Managed Account(11)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

1. On March 1, 2024, 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 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 achievement of a clinical milestone, as determined by The People, Culture and Compensation Committee of the Issuer Board of Directors on August 15, 2025.

2. 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 a tranche of restricted stock units granted to the reporting person on March 1, 2024.

3. The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $447.53 to $448.45. 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.

4. The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $449.21 to $450.16. 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.

5. The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $450.42 to $451.39. 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.

6. The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $451.48 to $452.48. 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.

7. The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $452.49 to $453.49. 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.

8. The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $453.50 to $454.45. 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.

9. The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $454.58 to $455.55. 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.

10. The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $455.65 to $456.00. 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.

11. 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.

	By: Brett Budzinski, Attorney-in-Fact For: Yvonne Greenstreet	08/19/2025
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

FAQ

What triggered the issuance of 14,252 shares to Yvonne Greenstreet?

The shares were issued upon vesting of 30% of a performance-based stock unit granted 03/01/2024 after a clinical milestone was determined by the People, Culture and Compensation Committee on 08/15/2025.

Why were shares sold on 08/18/2025 according to the Form 4 for ALNY?

The filing states the shares were automatically sold pursuant to a mandatory sell-to-cover provision in the award agreement to cover minimum statutory tax withholding obligations that became due upon vesting and settlement.

How did Greenstreet's direct ownership change after these transactions?

Direct beneficial ownership reported moved from 63,200 shares to 56,221 shares following the reported sales and issuance.

Are the reported sale prices exact per-trade amounts?

The filing reports weighted average sales prices for groups of transactions (ranges provided) and notes the reporting person can provide breakdowns of shares sold at each price upon request.

Does the Form 4 show any indirect holdings for Yvonne Greenstreet?

Yes, the filing reports 407 shares held indirectly via a managed account and additional shares acquired under the issuer 401(k) matching contribution program.