# EDGAR Filing Document

**Accession Number:** 0001757770
**File Stem:** 0001193125-26-041267
**Filing Date:** 2026-2
**Character Count:** 8518
**Document Hash:** 4cb7a8462314af3504742e0b101677a7
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001193125-26-041267.hdr.sgml**: 20260206

**ACCESSION NUMBER**: 0001193125-26-041267

**CONFORMED SUBMISSION TYPE**: SCHEDULE 13G/A

**PUBLIC DOCUMENT COUNT**: 1

**FILED AS OF DATE**: 20260206

**DATE AS OF CHANGE**: 20260206

**SUBJECT COMPANY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Alector, Inc.
- **CENTRAL INDEX KEY:** 0001653087
- **STANDARD INDUSTRIAL CLASSIFICATION:** BIOLOGICAL PRODUCTS (NO DIAGNOSTIC SUBSTANCES) [2836]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 822933343
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13G/A
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 005-90858
- **FILM NUMBER:** 26608105

**BUSINESS ADDRESS:**
- **STREET 1:** 131 OYSTER POINT BLVD., SUITE 600
- **CITY:** SOUTH SAN FRANCISCO
- **STATE:** CA
- **ZIP:** 94080
- **BUSINESS PHONE:** 415-231-5660

**MAIL ADDRESS:**
- **STREET 1:** 131 OYSTER POINT BLVD., SUITE 600
- **CITY:** SOUTH SAN FRANCISCO
- **STATE:** CA
- **ZIP:** 94080

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Alector LLC
- **DATE OF NAME CHANGE:** 20150915
**FILED BY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Rosenthal Arnon
- **CENTRAL INDEX KEY:** 0001757770

**ORGANIZATION NAME:**

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13G/A

**MAIL ADDRESS:**
- **STREET 1:** C/O ALECTOR, INC.
- **STREET 2:** 151 OYSTER POINT BLVD., #300
- **CITY:** SOUTH SAN FRANCISCO
- **STATE:** CA
- **ZIP:** 94080

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

## SCHEDULE 13G

### Under the Securities Exchange Act of 1934

**(Amendment No. 3)**

**Issuer:** Alector, Inc.

**Title of Class of Securities:** Common Stock, $0.0001 par value per share

**CUSIP Number:** 014442107

**Date of Event Which Requires Filing of this Statement:** 12/31/2025

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

- [ ] Rule 13d-1(b)

- [ ] Rule 13d-1(c)

- [x] Rule 13d-1(d)

---

| 1. | Names of Reporting Persons<br>Arnon Rosenthal | Names of Reporting Persons<br>Arnon Rosenthal |
|:---|:---|:---|:---|
| 2. | Check the Appropriate Box if a Member of a Group (See Instructions)<br>(a) [ ] (b) [ ] | Check the Appropriate Box if a Member of a Group (See Instructions)<br>(a) [ ] (b) [ ] |
| 3. | SEC Use Only | SEC Use Only |
| 4. | Citizenship or Place of Organization<br>X1 | Citizenship or Place of Organization<br>X1 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 5. | Sole Voting Power<br>4283550 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 6. | Shared Voting Power<br>3930375 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 7. | Sole Dispositive Power<br>4283550 |
| Number of<br>Shares<br>Beneficially<br>Owned by<br>Each<br>Reporting<br>Person<br>With | 8. | Shared Dispositive Power<br>3930375 |
| 9. | Aggregate Amount Beneficially Owned by Each Reporting Person<br>8213925 | Aggregate Amount Beneficially Owned by Each Reporting Person<br>8213925 |
| 10. | Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions) [ ] | Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions) [ ] |
| 11. | Percent of Class Represented by Amount in Row (9)<br>7.4% | Percent of Class Represented by Amount in Row (9)<br>7.4% |
| 12. | Type of Reporting Person (See Instructions)<br>IN | Type of Reporting Person (See Instructions)<br>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.

---

**Item 1(a). Name of Issuer:**
Alector, Inc.

**Item 1(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

**Item 2(b). Address of Principal Business Office:**
c/o Alector, Inc.
131 Oyster Point Blvd., Suite 600
South San Francisco, California 94080

**Item 2(c). Citizenship:**
United States

**Item 2(d). Title of Class of Securities:**
Common Stock, $0.0001 par value per share

**Item 2(e). CUSIP Number:**
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 Five Percent or Less of a Class.**

[x] If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following.

**Item 6. Ownership of More than 5 Percent on Behalf of Another Person.**

Not Applicable

**Item 7. Identification and Classification of the Subsidiary**

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. Certification:**

—

### 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**

**Date:** 02/04/2026

**By:** /s/Arnon Rosenthal

**Name & Title:** Arnon Rosenthal