Form 8-A12B TRex Bio, Inc.

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-A

For Registration of Certain Classes of Securities

Pursuant to Section 12(b) or (g) of the

Securities Exchange Act of 1934

TREX BIO, INC.

(Exact name of registrant as specified in its charter)

Securities to be registered pursuant to Section 12(b) of the Act:

If this form relates to the registration of a class of securities pursuant to Section 12(b) of the Exchange Act and is effective pursuant to General Instruction A.(c) or (e), check the following box. ☒

If this form relates to the registration of a class of securities pursuant to Section 12(g) of the Exchange Act and is effective pursuant to General Instruction A.(d) or (e), check the following box. o

If this form relates to the registration of a class of securities concurrently with a Regulation A offering, check the following box. o

Securities Act registration statement or Regulation A offering statement file number to which this form relates (if applicable): 333-299018

Securities to be registered pursuant to Section 12(g) of the Act: None

Item 1. Description of Registrant’s Securities to be Registered.

TRex Bio, Inc. (the “Registrant”) hereby incorporates by reference the description of its common stock, $0.0001 par value per share, to be registered hereunder, contained under the heading “Description of Capital Stock” in the prospectus that constitutes part of the Registrant’s Registration Statement on Form S-1 (File No. 333-299018) initially filed with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Act”), on September 18, 2026 (as amended from time to time, the “Registration Statement”). Any form of prospectus subsequently filed by the Registrant with the Commission pursuant to Rule 424(b) under the Act that constitutes part of the Registration Statement shall also be deemed to be incorporated herein by reference.

Item 2. Exhibits.

Pursuant to the Instructions as to Exhibits with respect to Form 8-A, no exhibits are filed herewith or incorporated herein by reference.

SIGNATURE

Pursuant to the requirements of Section 12 of the Securities Exchange Act of 1934, as amended, the Registrant has duly caused this registration statement to be signed on its behalf by the undersigned, thereto duly authorized.