June 2, 2026

Stem, Inc.
1400 Post Oak Boulevard, Suite 560
Houston, Texas 77056

Re:    Stem, Inc.
Registration Statement on Form S-3

Ladies and Gentlemen:

We have examined the Registration Statement on Form S-3 (the “Registration Statement”) to be filed by Stem, Inc., a Delaware corporation (the “Company”) with the Securities and Exchange Commission (the “Commission”) on the date hereof pursuant to the Securities Act of 1933, as amended (the “Securities Act”), in connection with the resale from time to time by the selling shareholder named in the Registration Statement (the “Selling Shareholder”) of up to 389,569 shares of the Company’s common stock, par value $0.0001 per share (the “Shares”). The Shares are to be offered by the Selling Shareholder for sale from time to time to the public as described in the Registration Statement.

In arriving at the opinions expressed below, we have examined originals, or copies certified or otherwise identified to our satisfaction as being true and complete copies of the originals, of specimen Common Stock certificate and such other documents, corporate records, certificates of officers of the Company and of public officials and other instruments as we have deemed necessary or advisable to enable us to render the opinions set forth below. In our examination, we have assumed, without independent investigation, the genuineness of all signatures, the legal capacity and competency of all natural persons, the authenticity of all documents submitted to us as originals and the conformity to original documents of all documents submitted to us as copies.

Based upon the foregoing and in reliance thereon, and subject to the assumptions, exceptions, qualifications and limitations set forth herein, we are of the opinion that the Shares are validly issued, fully paid and non-assessable.

The opinion expressed above is subject to the following exceptions, qualifications, limitations and assumptions:

A.We render no opinion herein as to matters involving the laws of any jurisdiction other than the State of New York and the United States of America and the Delaware General Corporation Law. We are not admitted to practice in the State of Delaware; however, we are generally familiar with the Delaware General Corporation Law as currently in effect and have made such inquiries as we consider necessary to render the opinion contained herein. Without limitation, we do not express any opinion regarding any Delaware contract law. This opinion is limited to the effect of the current state of the laws of the State of New York, the

Gibson, Dunn & Crutcher LLP 200 Park Avenue | New York, NY 10166-0193 | T: 212.351.4000 | F: 212.351.4035 | gibsondunn.com

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United States of America and, to the limited extent set forth above, the laws of the State of Delaware and the facts as they currently exist. We assume no obligation to revise or supplement this opinion in the event of future changes in such laws or the interpretations thereof or such facts.

We consent to the filing of this opinion as an exhibit to the Registration Statement, and we further consent to the use of our name under the caption “Legal Matters” in the Registration Statement and the prospectus that forms a part thereof. In giving these consents, we do not thereby admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission promulgated thereunder.

Very truly yours, /s/ GIBSON, DUNN & CRUTCHER LLP