Perceptive Advisors Reports 2.48M ACLX Shares; 4.5% Ownership

Rhea-AI Filing Summary

Perceptive Advisors and affiliated parties reported beneficial ownership of 2,478,000 shares of Arcellx, Inc. (ACLX), representing 4.5% of the outstanding common stock based on 55,458,912 shares outstanding as of August 1, 2025. The filing shows the Master Fund directly holds the 2,478,000 shares, with Perceptive Advisors serving as investment manager and Joseph Edelman identified as managing member. All three reporting persons report shared voting and dispositive power over those shares and report no sole voting or dispositive power. The Schedule 13G/A is filed under the passive investor framework and contains standard certifications and signatures by Joseph Edelman.

Positive

• Clear disclosure of beneficial ownership amounting to 2,478,000 shares and the basis for the percentage calculation
• Identification of relationship between Perceptive Advisors, the Master Fund, and Joseph Edelman clarifies control and manager roles

Negative

• None.

Insights

Financial Analyst

TL;DR: A well-documented passive 4.5% stake is disclosed, below the 5% threshold and unlikely to change control dynamics.

The Schedule 13G/A discloses a 4.5% beneficial ownership position in Arcellx by Perceptive Advisors, its Master Fund, and Joseph Edelman. The position is reported as shared voting and dispositive power, with no sole control. Because the filing uses Schedule 13G/A language consistent with passive investment reporting and the stake is under 5% of the float, this disclosure is informational and indicates monitoring interest rather than an active control campaign. The filing references the issuer share count used to calculate percentage, ensuring the ownership percentage is transparent.

Corporate Governance Expert

TL;DR: Disclosure clarifies ownership and voting arrangements but does not signal governance change.

The report attributes shared voting and dispositive power to Perceptive Advisors and Joseph Edelman for the 2,478,000 shares held by the Master Fund. This explicit identification of roles reduces ambiguity about who directs voting decisions. However, at 4.5% ownership the position remains below common thresholds that typically trigger formal governance influence or mandatory takeover filings. The filing contains standard certifications and signatures, meeting regulatory disclosure obligations.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 4)

Arcellx, Inc.

(Name of Issuer)

Common Stock, par value $0.001 per share

(Title of Class of Securities)

03940C100

(CUSIP Number)

06/30/2025

(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. 03940C100

1

Names of Reporting Persons

Perceptive Advisors LLC

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

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 2,478,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 2,478,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

2,478,000.00

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)

4.5 %

12

Type of Reporting Person (See Instructions)

IA

SCHEDULE 13G

CUSIP No. 03940C100

1

Names of Reporting Persons

Joseph Edelman

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 0.00
6	Shared Voting Power 2,478,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 2,478,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

2,478,000.00

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)

4.5 %

12

Type of Reporting Person (See Instructions)

IN

SCHEDULE 13G

CUSIP No. 03940C100

1

Names of Reporting Persons

Perceptive Life Sciences Master Fund, Ltd.

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

CAYMAN ISLANDS

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 2,478,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 2,478,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

2,478,000.00

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)

4.5 %

12

Type of Reporting Person (See Instructions)

CO

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Arcellx, Inc.
(b)	Address of issuer's principal executive offices: 800 Bridge Parkway, Redwood City, CA 94065
Item 2.
(a)	Name of person filing: The names of the persons filing this report (collectively, the "Reporting Persons") with respect to shares of Common Stock, par value $0.001 per share (the "Common Stock") of Arcellx, Inc. (the "Issuer") are: (i) Perceptive Advisors LLC ("Perceptive Advisors") (ii) Joseph Edelman ("Mr. Edelman") (iii) Perceptive Life Sciences Master Fund, Ltd. (the "Master Fund")
(b)	Address or principal business office or, if none, residence: The address of the principal business office of each of the Reporting Persons is: 51 Astor Place, 10th Floor, New York, NY 10003
(c)	Citizenship: Perceptive Advisors is a Delaware limited liability company. Mr. Edelman is a United States citizen. The Master Fund is a Cayman Islands corporation.
(d)	Title of class of securities: Common Stock, par value $0.001 per share
(e)	CUSIP No.: 03940C100
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: The information required by this item with respect to each Reporting Person is set forth in Rows 5 through 9 of the cover pages to this Schedule 13G. The ownership percentages reported are based on 55,458,912 shares of Common Stock outstanding as of August 1, 2025, as reported in the Issuer's Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on August 7, 2025. The Master Fund directly holds 2,478,000 shares of Common Stock. Perceptive Advisors serves as the investment manager to the Master Fund. Mr. Edelman is the managing member of Perceptive Advisors.
(b)	Percent of class: Perceptive Advisors: 4.5% Mr. Edelman: 4.5% Master Fund: 4.5%
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: Perceptive Advisors: 0 Mr. Edelman: 0 Master Fund: 0
	(ii) Shared power to vote or to direct the vote: Perceptive Advisors: 2,478,000 Mr. Edelman: 2,478,000 Master Fund: 2,478,000
	(iii) Sole power to dispose or to direct the disposition of: Perceptive Advisors: 0 Mr. Edelman: 0 Master Fund: 0
	(iv) Shared power to dispose or to direct the disposition of: Perceptive Advisors: 2,478,000 Mr. Edelman: 2,478,000 Master Fund: 2,478,000
Item 5.	Ownership of 5 Percent or Less of a Class.
	Ownership of 5 percent or less of a class
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.

Perceptive Advisors LLC

Signature:	/s/ Joseph Edelman
Name/Title:	Joseph Edelman, Managing Member
Date:	08/14/2025

Joseph Edelman

Signature:	/s/ Joseph Edelman
Name/Title:	Joseph Edelman
Date:	08/14/2025

Perceptive Life Sciences Master Fund, Ltd.

Signature:	/s/ Joseph Edelman
Name/Title:	Joseph Edelman, Managing Member
Date:	08/14/2025

FAQ

What percentage of Arcellx (ACLX) does Perceptive Advisors report owning?

Perceptive Advisors and affiliated reporting persons disclose beneficial ownership of 2,478,000 shares, representing 4.5% of ACLX common stock based on 55,458,912 shares outstanding as of August 1, 2025.

Does the filing indicate Perceptive Advisors has sole voting control over ACLX shares?

No. The filing reports 0 shares with sole voting power and 2,478,000 shares with shared voting power.

Who directly holds the reported ACLX shares?

The Schedule states that Perceptive Life Sciences Master Fund, Ltd. directly holds the 2,478,000 shares, with Perceptive Advisors as investment manager and Joseph Edelman as managing member.

Was this filing made under the passive investor rules?

Yes. The Schedule 13G/A format and the reporting context indicate the position is disclosed under the passive investor framework rather than an active Section 13(d) control filing.

When was the Schedule 13G/A signed?

The signatures on the filing are dated 08/14/2025 signed by Joseph Edelman for the reporting entities.