Arnon Rosenthal discloses 7.4% Alector (ALEC) stake in Schedule 13G/A

Rhea-AI Filing Summary

Alector, Inc. insider ownership update: Arnon Rosenthal reports beneficial ownership of 8,213,925 shares of Alector common stock, representing 7.4% of the outstanding shares based on 109,151,472 shares outstanding as of October 31, 2025.

The holding includes 1,736,295 shares owned directly, 132,804 shares issuable from restricted stock units vesting within 60 days of December 31, 2025, and 2,414,451 shares issuable upon option exercises within the same period. He also has shared voting and dispositive power over 3,930,375 shares held through family trusts for which he serves as trustee.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 3)

Alector, Inc.

(Name of Issuer)

Common Stock, $0.0001 par value per share

(Title of Class of Securities)

014442107

(CUSIP Number)

12/31/2025

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

SCHEDULE 13G

CUSIP No. 014442107

1

Names of Reporting Persons

Arnon Rosenthal

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 4,283,550.00
6	Shared Voting Power 3,930,375.00
7	Sole Dispositive Power 4,283,550.00
8	Shared Dispositive Power 3,930,375.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

8,213,925.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

7.4 %

12

Type of Reporting Person (See Instructions)

IN

Comment for Type of Reporting Person: With respect to Rows 5, 7, and 9, includes: (i) 1,736,295 shares of common stock held of record by Arnon Rosenthal (the "Reporting Person"), (ii) 132,804 shares of common stock that are issuable upon vesting of restricted stock units within 60 days of December 31, 2025 to the Reporting Person, and (iii) 2,414,451 shares of common stock that are issuable upon exercise of outstanding options within 60 days of December 31, 2025 to the Reporting Person. With respect to Rows 6, 8, and 9, includes (i) 1,972,875 shares of common stock held of record by The Rosenthal Family Revocable Trust Dated November 4, 1994, as restated on June 9, 1999, for which the Reporting Person serves as trustee; (ii) 652,500 shares of common stock held of record by The Adi Rosenthal 2007 Trust dated March 27, 2007, for which the Reporting Person serves as trustee; (iii) 652,500 shares of common stock held of record by The Noam Rosenthal 2007 Trust dated March 27, 2007, for which the Reporting Person serves as trustee and (iv) 652,500 shares of common stock held of record by The Shani Rosenthal 2007 Trust dated March 27, 2007, for which the Reporting Person serves as trustee. With respect to Row 11, the percentage ownership is based on 109,151,472 shares of the Issuer's common stock outstanding as of October 31, 2025, as reported in the Issuer's Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2025, filed with the Securities and Exchange Commission on November 6, 2025.

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Alector, Inc.
(b)	Address of issuer's principal executive offices: 131 Oyster Point Blvd., Suite 600 South San Francisco, California 94080
Item 2.
(a)	Name of person filing: Arnon Rosenthal
(b)	Address or principal business office or, if none, residence: c/o Alector, Inc. 131 Oyster Point Blvd., Suite 600 South San Francisco, California 94080
(c)	Citizenship: United States
(d)	Title of class of securities: Common Stock, $0.0001 par value per share
(e)	CUSIP No.: 014442107
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.	Ownership
(a)	Amount beneficially owned: See Row 9 of cover page.
(b)	Percent of class: See Row 5 of cover page for the Reporting Person.
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: See Row 11 of cover page.
	(ii) Shared power to vote or to direct the vote: See Row 6 of cover page for the Reporting Person.
	(iii) Sole power to dispose or to direct the disposition of: See Row 7 of cover page for the Reporting Person.
	(iv) Shared power to dispose or to direct the disposition of: See Row 8 of cover page for the Reporting Person.
Item 5.	Ownership of 5 Percent or Less of a Class.
	Not Applicable
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	Not Applicable
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	Not Applicable
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.	Certifications:
	Not Applicable

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Arnon Rosenthal

Signature:	/s/Arnon Rosenthal
Name/Title:	Arnon Rosenthal
Date:	02/04/2026

FAQ

How many Alector (ALEC) shares does Arnon Rosenthal beneficially own?

Arnon Rosenthal beneficially owns 8,213,925 shares of Alector common stock. This total combines directly held shares, shares underlying restricted stock units and stock options vesting or exercisable within 60 days of December 31, 2025, plus shares held through several family trusts he oversees.

What percentage of Alector (ALEC) does Arnon Rosenthal’s 13G/A filing report?

The filing reports that Arnon Rosenthal beneficially owns 7.4% of Alector’s common stock. This percentage is calculated using 109,151,472 shares outstanding as of October 31, 2025, as disclosed in Alector’s Form 10-Q for the quarter ended September 30, 2025.

How many Alector (ALEC) shares does Arnon Rosenthal hold directly versus through equity awards?

Rosenthal directly holds 1,736,295 shares of Alector common stock. He also has 132,804 shares issuable from restricted stock units and 2,414,451 shares issuable upon exercise of stock options that become exercisable within 60 days of December 31, 2025.

What Alector (ALEC) shares are attributed to family trusts in this Schedule 13G/A?

The filing attributes 3,930,375 shares to family trusts for which Rosenthal is trustee. These include 1,972,875 shares in The Rosenthal Family Revocable Trust and three separate 2007 trusts (Adi, Noam, and Shani Rosenthal), each holding 652,500 shares of Alector common stock.

What voting and dispositive powers does Arnon Rosenthal report over Alector (ALEC) shares?

Rosenthal reports sole voting and dispositive power over 4,283,550 shares and shared voting and dispositive power over 3,930,375 shares. The shared powers relate to shares held in the Rosenthal family trusts where he acts as trustee, giving him joint control over those holdings.

What event date and period does this Alector (ALEC) Schedule 13G/A cover?

The event requiring this Schedule 13G/A amendment is dated December 31, 2025. Percentage ownership is based on Alector’s 109,151,472 shares outstanding as of October 31, 2025, as disclosed in the company’s Form 10-Q filed on November 6, 2025.