Initial Registration Statement for Employee Benefit Plan (Form S-8)

As filed with the U.S. Securities and Exchange Commission on November 3, 2026

Registration No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

_____________________________________

FORM S-8

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

_____________________________________

FAETH THERAPEUTICS, INC.

(Exact name of registrant as specified in its charter)

_____________________________________

701 Tillery Street #12 #1010
Austin, Texas 78702

(Address of principal executive offices) (Zip code)

_____________________________________

2026 Equity Incentive Plan

2026 Employee Stock Purchase Plan

(Full title of the plan)

_____________________________________

Christopher W. Gerry

General Counsel and Secretary

Faeth Therapeutics, Inc.

701 Tillery Street #12 #1010

Austin, Texas 78702

(512) 200-2982

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

Copies to:

_____________________________________

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.

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. ¨

EXPLANATORY NOTE

Faeth Therapeutics, Inc., formerly known as Sensei Biotherapeutics, Inc. (the "Registrant"), is filing this Registration Statement on Form S-8 (this "Registration Statement") to register (i) 2,671,981 shares of its common stock, par value $0.0001 per share ("Common Stock"), reserved for issuance under the Registrant's 2026 Equity Incentive Plan (the "2026 Plan"); (ii) up to 311,164 shares of Common Stock subject to outstanding stock awards granted under the Registrant's 2021 Equity Incentive Plan (the "2021 Plan") that, following the effective date of the 2026 Plan, may become available for issuance under the 2026 Plan because the award expires or otherwise terminates without all of the shares covered by the award having been issued, is settled in cash, is forfeited or repurchased because of the failure to vest, or is reacquired or withheld to satisfy a tax withholding obligation or the purchase or exercise price (the "Returning Shares"); and (iii) 267,198 shares of Common Stock reserved for issuance under the Registrant's 2026 Employee Stock Purchase Plan (the "2026 ESPP").

The 2026 Plan and the 2026 ESPP were approved by the Registrant's board of directors on April 10, 2026 and by the Registrant's stockholders at the Registrant's 2026 annual meeting of stockholders held on June 10, 2026. On June 15, 2026, the Registrant changed its name from Sensei Biotherapeutics, Inc. to Faeth Therapeutics, Inc.

PART I

INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

ITEM 1. PLAN INFORMATION.

Not required to be filed with this Registration Statement.

ITEM 2. REGISTRANT INFORMATION AND EMPLOYEE PLAN ANNUAL INFORMATION.

Not required to be filed with this Registration Statement.

PART II ITEM 3. INCORPORATION OF DOCUMENTS BY REFERENCE

The Registrant hereby incorporates by reference into this Registration Statement the following documents previously filed by the Registrant with the Securities and Exchange Commission (the "SEC"):

(a) The Registrant's Annual Report on Form 10-K for the fiscal year ended December 31, 2025, filed with the SEC on March 30, 2026, as amended by Amendment No. 1 on Form 10-K/A, filed with the SEC on June 2, 2026;

(b) The information specifically incorporated by reference into the Registrant's Annual Report on Form 10-K for the fiscal year ended December 31, 2025 from the Registrant's Definitive Proxy Statement on Schedule 14A, filed with the SEC on April 27, 2026;

(c) The Registrant's Quarterly Reports on Form 10-Q for the quarters ended March 31, 2026, June 30, 2026 and September 30, 2026, filed with the SEC on May 15, 2026, August 4, 2026 and November 3, 2026, respectively;

(d) The Registrant's Current Reports on Form 8-K filed with the SEC on February 13, 2026, February 18, 2026 (as amended by the Current Report on Form 8-K/A filed with the SEC on April 15, 2026), April 16, 2026, May 21, 2026, May 22, 2026, June 10, 2026, June 15, 2026, June 18, 2026, July 23, 2026, and September 17, 2026 and October 27, 2026 (except that, with respect to the foregoing Current Reports, any portions thereof which are furnished and not filed shall not be deemed incorporated by reference); and

(e) The description of the Registrant's Common Stock, which is registered under Section 12 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), contained in Exhibit 4.1 to the Registrant's Amendment No. 2 to the Registration Statement on Form S-3 (File No. 333-295362), filed with the SEC on June 10, 2026, including all amendments or reports filed for the purpose of updating such description.

All documents, reports and definitive proxy or information statements filed pursuant to Section 13(a), 13(c), 14 or 15(d) of the Exchange Act after the date of this Registration Statement and prior to the filing of a post-effective amendment which indicates that all securities offered hereby have been sold or which deregisters all securities then remaining unsold, shall be deemed to be incorporated by reference into this Registration Statement and to be a part hereof from the date of filing of such documents; provided, however, that documents, reports and definitive proxy or information statements, or portions thereof, which are furnished and not filed in accordance with the rules of the SEC shall not be deemed incorporated by reference into this Registration Statement. Any statement contained in a document incorporated or deemed to be incorporated herein by reference shall be deemed to be modified or superseded for purposes of this Registration Statement to the extent that a statement herein or in any other subsequently filed document which also is or is deemed to

be incorporated by reference herein modifies or supersedes that statement. Any such statement so modified or superseded shall not constitute a part of this Registration Statement, except as so modified or superseded.

ITEM 4. DESCRIPTION OF SECURITIES.

Not applicable.

ITEM 5. INTERESTS OF NAMED EXPERTS AND COUNSEL.

Not applicable.

ITEM 6. INDEMNIFICATION OF DIRECTORS AND OFFICERS.

Section 145 of the Delaware General Corporation Law authorizes a court to award, or a corporation's board of directors to grant, indemnity to directors and officers in terms sufficiently broad to permit such indemnification under certain circumstances for liabilities, including reimbursement for expenses incurred, arising under the Securities Act of 1933, as amended (the "Securities Act"). The Registrant's amended and restated certificate of incorporation, as amended, permits indemnification of its directors, officers, employees and other agents to the maximum extent permitted by the Delaware General Corporation Law, and the Registrant's amended and restated bylaws provide that the Registrant will indemnify its directors and executive officers and permit it to indemnify its other officers, employees, and other agents, in each case to the maximum extent permitted by the Delaware General Corporation Law.

The Registrant has entered into indemnification agreements with its directors and executive officers, whereby it has agreed to indemnify its directors and executive officers to the fullest extent permitted by law, including indemnification against expenses and liabilities incurred in legal proceedings to which the director or executive officer was, or is threatened to be made, a party by reason of the fact that such director or executive officer is or was a director, executive officer, employee or agent of the Registrant, provided that such director or executive officer acted in good faith and in a manner that the director or executive officer reasonably believed to be in, or not opposed to, the best interest of the Registrant.

The Registrant maintains insurance policies that indemnify its directors and officers against various liabilities arising under the Securities Act and the Exchange Act that might be incurred by any director or officer in his or her capacity as such.

ITEM 7. EXEMPTION FROM REGISTRATION CLAIMED.

Not applicable.

ITEM 8. EXHIBITS

* Filed herewith.

# Indicates management contract or compensatory plan.

ITEM 9. UNDERTAKINGS.

(a) The undersigned Registrant hereby undertakes:

(1) To file, during any period in which offers or sales are being made, a post-effective amendment to this Registration Statement:

(i) To include any prospectus required by Section 10(a)(3) of the Securities Act;

(ii) To reflect in the prospectus any facts or events arising after the effective date of the Registration Statement (or the most recent post-effective amendment thereof) which, individually or in the aggregate, represent a fundamental change in the information set forth in the Registration Statement. Notwithstanding the foregoing, any increase or

decrease in volume of securities offered (if the total dollar value of securities offered would not exceed that which was registered) and any deviation from the low or high end of the estimated maximum offering range may be reflected in the form of prospectus filed with the SEC pursuant to Rule 424(b) if, in the aggregate, the changes in volume and price represent no more than a 20% change in the maximum aggregate offering price set forth in the "Calculation of Registration Fee" table in the effective Registration Statement; and

(iii) To include any material information with respect to the plan of distribution not previously disclosed in the Registration Statement or any material change to such information in the Registration Statement;

provided, however, that paragraphs (a)(1)(i) and (a)(1)(ii) do not apply if the information required to be included in a post-effective amendment by those paragraphs is contained in reports filed with or furnished to the SEC by the Registrant pursuant to Section 13 or Section 15(d) of the Exchange Act that are incorporated by reference in the Registration Statement.

(2) That, for the purpose of determining any liability under the Securities Act, each such post-effective amendment shall be deemed to be a new registration statement relating to the securities offered herein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(3) To remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering.

(b) The undersigned Registrant hereby undertakes that, for purposes of determining any liability under the Securities Act, each filing of the Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the Exchange Act (and, where applicable, each filing of an employee benefit plan's annual report pursuant to Section 15(d) of the Exchange Act) that is incorporated by reference in the Registration Statement shall be deemed to be a new registration statement relating to the securities offered herein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(c) Insofar as indemnification for liabilities arising under the Securities Act may be permitted to directors, officers and controlling persons of the Registrant pursuant to the foregoing provisions, or otherwise, the Registrant has been advised that in the opinion of the SEC such indemnification is against public policy as expressed in the Securities Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the Registrant of expenses incurred or paid by a director, officer or controlling person of the Registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the Registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Securities Act and will be governed by the final adjudication of such issue.

SIGNATURES

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-8 and has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in Austin, Texas, on November 3, 2026.

POWER OF ATTORNEY

KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears below hereby constitutes and appoints Anand Parikh and Brian Stephenson, and each of them, as his or her true and lawful attorneys-in-fact, proxies and agents, each with full power of substitution and resubstitution, for him or her in his or her name, place and stead, in any and all capacities, to sign any and all amendments to this Registration Statement (including post-effective amendments or any abbreviated registration statement and any amendments thereto filed pursuant to Rule 462(b) increasing the number of securities for which registration is sought), and to file the same, with all exhibits thereto and other documents in connection therewith, with the SEC and generally to do all such things in his or her name and behalf in his or her capacity as officers and directors to enable the Registrant to comply with the provisions of the Securities Act and all requirements of the SEC, granting unto said attorneys-in-fact, proxies and agents, and each of them, full power and authority to do and perform each and every act and thing requisite and necessary to be done in connection therewith, as fully for all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact, proxies and agents, or their or his or her substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, as amended, this Registration Statement has been signed by the following persons in the capacities and on the dates indicated.