Gilead completes Arcellx merger; Arcellx (NASDAQ: ACLX) deregisters S-3

Rhea-AI Filing Summary

Arcellx, Inc. has filed a post-effective amendment to deregister all securities remaining unsold under its Form S-3 following the closing of a merger in which Arcellx became a wholly owned subsidiary of Gilead Sciences on April 28, 2026. The amendment states the Registrant terminated offerings under the Registration Statement pursuant to an Agreement and Plan of Merger dated February 22, 2026, and that, after this filing, no securities remain registered under Registration No. 333-271731.

Insights

Corporate Transactions Attorney

Merger-driven deregistration closes the shelf; legal obligations preserved.

The filing formally removes from registration any unsold securities under the referenced Form S-3, completing the registrant's post-offering cleanup after the Merger with Gilead Sciences. The amendment cites the Merger Agreement dated February 22, 2026.

Key dependencies include the operative Merger Agreement (Exhibit 2.1 to the 8-K filed February 23, 2026) and the registrant's prior undertakings to remove unsold securities by post-effective amendment; subsequent filings will show any further administrative steps.

Corporate Finance Analyst

This action reflects administrative wind‑down of public registration after acquisition.

The amendment terminates the effectiveness of Registration No. 333-271731 and removes all unsold securities from registration, consistent with the company becoming a wholly owned subsidiary of Gilead on April 28, 2026. Cash‑flow treatment is not stated in the excerpt.

Investors should consult the cited Merger Agreement and the referenced Form 8-K for transaction economics and any related consideration disclosed there.

Key Figures

Registration Number: 333-271731 Merger Closing Date: April 28, 2026 Merger Agreement Date: February 22, 2026 +1 more

4 metrics

Registration Number 333-271731 Form S-3 registration referenced in the amendment

Merger Closing Date April 28, 2026 Date Merger closed and filing executed

Merger Agreement Date February 22, 2026 Date of the Agreement and Plan of Merger among Arcellx, Parent and Merger Sub

EIN 47-2855917 Registrant's I.R.S. Employer Identification Number

Key Terms

Post-Effective Amendment, Registration Statement, Agreement and Plan of Merger, deregister

4 terms

Post-Effective Amendment regulatory

"DEREGISTRATION OF SECURITIES This Post-Effective Amendment (this “Post-Effective Amendment”) is being filed"

A post-effective amendment is an official update to a securities registration document filed after that document has become effective with regulators; it corrects, adds or replaces information about the securities, the company, or an offering. Investors care because it keeps the legal record current and can change what is being sold or the rights attached to shares — like getting a revised product manual after a launch that may affect value or use.

Registration Statement regulatory

"registered but unsold or otherwise unissued as of the date hereof under the following Registration Statement on Form S-3"

A registration statement is a formal document that companies file with a government agency to offer new shares of stock to the public. It provides essential information about the company's finances, operations, and risks, helping investors make informed decisions. Think of it as a detailed product description that ensures transparency and trust before buying into a company.

Agreement and Plan of Merger legal

"pursuant to an Agreement and Plan of Merger (the “Merger Agreement”), dated as of February 22, 2026"

An Agreement and Plan of Merger is a formal document where two companies agree to combine into one, outlining how the process will happen. It’s like a step-by-step plan for merging, and it matters because it shows both sides have agreed on the details before the official transition takes place.

deregister regulatory

"the Registrant hereby terminates the effectiveness of the Registration Statement and removes from registration all of the securities"

Deregister is the act of removing a company’s securities from a public regulatory registry or ending their listing on a stock exchange; think of it like taking a car off public roads so it no longer needs public inspections. For investors, deregistration matters because it usually reduces required public disclosures, can make shares harder to buy or sell, and increases uncertainty about the company’s finances and governance due to lower transparency and liquidity.

Offering Details

base_shelf_indeterminate

Offering

Offering Type base_shelf_indeterminate

As filed with the Securities and Exchange Commission on April 28, 2026

Registration No. 333-271731

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

POST- EFFECTIVE AMENDMENT NO. 1

TO

FORM S-3

REGISTRATION STATEMENT NO. 333-271731

UNDER

THE SECURITIES ACT OF 1933

Arcellx, Inc.

(Exact name of registrant as specified in its charter)

Delaware		47-2855917
(State or other jurisdiction of incorporation or organization)		(I.R.S. Employer Identification Number)

800 Bridge Parkway

Redwood City, CA 94065

(240) 327-0630

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Andrew D. Dickinson
President and Treasurer

Arcellx, Inc.

333 Lakeside Drive
Foster City, CA 94404

(240) 327-0630

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copy to:

Emily Oldshue

Nicholas Roper

Ropes & Gray LLP

Prudential Tower, 800 Boylston Street

Boston, Massachusetts 02199

(617) 951-7000

(Approximate date of commencement of proposed sale to the public): Not applicable.

If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box: ¨

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box:  ¨

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ¨

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ¨

If this Form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box.  x

If this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box.  ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer	x	Accelerated filer	¨
Non-accelerated filer	¨	Smaller reporting company	¨
		Emerging growth company	¨

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act.  ¨

DEREGISTRATION OF SECURITIES

This Post-Effective Amendment (this “Post-Effective Amendment”) is being filed by Arcellx, Inc. (the “Registrant”) to deregister any and all securities, registered but unsold or otherwise unissued as of the date hereof under the following Registration Statement on Form S-3 (the “Registration Statement”) previously filed by the Registrant with the U.S. Securities and Exchange Commission (the “SEC”):

· Registration Statement No. 333-271731, filed with the SEC on May 8, 2023, relating to the registration of (i) an unspecified number of the Company’s common stock, par value $0.001 per share (“Common Stock”), preferred stock, debt securities, warrants and/or units, with an unspecified aggregate offering price and (ii) up to $350 million of Common Stock that may be sold under that certain At-The-Market Equity Offering Sales Agreement, dated May 8, 2023, by and between the Company and Stifel, Nicolaus & Company, Incorporated.  

On April 28, 2026, pursuant to an Agreement and Plan of Merger (the “Merger Agreement”), dated as of February 22, 2026, by and among the Registrant, Gilead Sciences, Inc. (“Parent”) and Ravens Sub, Inc. (“Merger Sub”), Merger Sub merged with and into the Registrant (the “Merger”), with the Registrant continuing as the surviving corporation and becoming a wholly owned subsidiary of Parent. As a result of the transactions contemplated by the Merger Agreement, the Registrant has terminated any and all offerings and sales of securities pursuant to the Registration Statement. In accordance with the undertakings made by the Registrant in the Registration Statement to remove from registration, by means of a post-effective amendment, any of the securities of the Registrant registered under the Registration Statement which remain unsold at the termination of the offering, the Registrant hereby terminates the effectiveness of the Registration Statement and removes from registration all of the securities that remain unsold under the Registration Statement as of the date hereof, if any. The Registration Statement is hereby amended, as appropriate, to reflect the deregistration of such securities. After giving effect to this Post-Effective Amendment, there will be no remaining securities registered by the Registrant pursuant to the Registration Statement.

The foregoing description of the Merger, the Merger Agreement and the transactions contemplated thereby does not purport to be complete and is subject to, and qualified in its entirety by, the Merger Agreement, which is attached as Exhibit 2.1 to the Registrant’s Current Report on Form 8-K filed with the SEC on February 23, 2026.

SIGNATURE

Pursuant to the requirements of the Securities Act of 1933, as amended, the Registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this Post-Effective Amendment to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Redwood City, State of California, on April 28, 2026.

	ARCELLX, INC.
	By:	/s/ Andrew D. Dickinson
	Name:	Andrew D. Dickinson
	Title:	President and Treasurer

No other person is required to sign this Post-Effective Amendment in reliance upon Rule 478 under the Securities Act of 1933, as amended.

FAQ

What did ACLX file in this post-effective amendment?

Arcellx filed a post-effective amendment to deregister unsold securities under its Form S-3. The filing states the registrant terminated offerings and removed all unsold securities under Registration No. 333-271731 as of April 28, 2026.

Why did Arcellx (ACLX) deregister the securities?

Because Arcellx completed a merger making it a wholly owned subsidiary of Gilead Sciences. The amendment cites the Merger Agreement dated February 22, 2026, and the merger closing on April 28, 2026.

Does this filing disclose proceeds or amounts still registered for sale?

No dollar amounts or share counts remain registered under the referenced Registration Statement. The amendment states there will be no remaining securities registered under Registration No. 333-271731 after this filing.

Where can I find the Merger Agreement referenced in the ACLX filing?

The amendment references the Merger Agreement attached as Exhibit 2.1 to Arcellx’s Form 8-K filed February 23, 2026. That Form 8-K contains the Merger Agreement and related transaction descriptions.

Will Arcellx continue to have public registration obligations after this filing?

The amendment removes the unsold securities from this specific Registration Statement, leaving no securities registered under Registration No. 333-271731. Any future registration obligations would be governed by Parent or subsequent filings, not this S-3 registration.