October 9, 2026
TRex Bio, Inc.
269 East Grand Avenue, Suite 300
South San Francisco, CA 94080
Ladies and Gentlemen:
This opinion letter is furnished to you in connection with the registration statement on Form S‑8 (the “Registration Statement”), filed by TRex Bio, Inc., a Delaware corporation (the “Company”), on the date hereof, with the Securities and Exchange Commission under the Securities Act of 1933, as amended (the “Securities Act”), for the registration of 5,881,797 shares of Common Stock, $0.0001 par value per share, of the Company (the “Shares”). The Shares are issuable under the Company's 2024 Equity Incentive Plan, 2026 Equity Incentive Plan and 2026 Employee Stock Purchase Plan (each, a “Plan” and collectively, the “Plans”).
We are familiar with the actions taken by the Company in connection with the adoption of the Plans. We have examined such certificates, documents and records and have made such investigation of fact and such examination of law as we have deemed appropriate in order to enable us to render the opinions set forth herein. In conducting such investigation, we have relied, without independent verification, upon certificates of officers of the Company, public officials and other appropriate persons.
The opinions expressed below are limited to the Delaware General Corporation Law.
Based upon and subject to the foregoing, we are of the opinion that the Shares have been duly authorized and, when the Shares have been issued and sold in accordance with the terms of the applicable Plan, the Shares will be validly issued, fully paid and nonassessable.