Form 8-K

8-K — ClearSign Technologies Corp

Accession: 0001104659-26-080744

Filed: 2026-07-06

Period: 2026-07-06

CIK: 0001434524

SIC: 3823 (INDUSTRIAL INSTRUMENTS FOR MEASUREMENT, DISPLAY, AND CONTROL)

Item: Other Events

Item: Financial Statements and Exhibits

Documents

8-K — tm2619440d1_8k.htm (Primary)

EX-5.1 — EXHIBIT 5.1 (tm2619440d1_ex5-1.htm)

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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Date of report (Date of earliest event reported):

July 6, 2026

CLEARSIGN TECHNOLOGIES CORPORATION

(Exact name of registrant as specified in charter)

Delaware

001-35521

26-2056298

(State or other jurisdiction of

incorporation)

(Commission File Number)

(IRS Employer

Identification No.)

8023 E. 63rd Place, Suite 101

Tulsa,

Oklahoma 74133

(Address of principal executive offices

and zip code)

(918) 500-7312

(Registrant's telephone number, including area code)

Check the appropriate box below if the Form 8-K filing is intended

to simultaneously satisfy the filing obligation of the Registrant under any of the following provisions (see General Instruction A.2 below).

Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR240.14a-12)

Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

Pre-commencement communications pursuant to Rule 13e-4(c) under the

Exchange Act (17 CFR 240.13e-4(c))

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

Title of each class

Trading Symbol(s)

Name

of each exchange on which

registered

Common Stock

CLIR

The Nasdaq Stock Market LLC

Indicate by check mark whether the registrant is an emerging growth

company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange

Act of 1934 (§240.12b-2 of this chapter).

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 13(a) of the Exchange Act. ¨

Item 8.01

Other Events.

July 6, 2026, ClearSign Technologies Corporation (the “Company”) filed a prospectus supplement (the “Prospectus Supplement”)

to recommence its “at the market” offering, as defined in Rule 415 under the Securities Act of 1933, as amended, under which

the Company may offer and sell up to $6,875,000 in shares (the “Placement Shares”)

of the Company’s common stock, par value $0.0001 per share, pursuant to that certain At The Market Offering Agreement between the

Company and H.C. Wainwright & Co., LLC, dated July 17, 2025 (the “Sales Agreement”).

The

issuance and sale of the Placement Shares by the Company under the Sales Agreement

will be made pursuant to the Company’s registration statement on Form S-3 (File No. 333-288736) filed with the Securities and Exchange

Commission on July 17, 2025, and declared effective on July 28, 2025, as supplemented by the Prospectus Supplement.

copy of the legal opinion of Mitchell Silberberg & Knupp LLP relating to the Placement Shares is filed as Exhibit 5.1 hereto.

Item 9.01

Financial Statements and Exhibits.

(d) Exhibits.

Exhibit No.

Description

5.1

Opinion of Mitchell Silberberg & Knupp LLP.

23.1

Consent of Mitchell Silberberg & Knupp LLP (included in Exhibit 5.1).

104

Cover Page Interactive Data File (embedded within the Inline XBRL document).

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf

by the undersigned hereunto duly authorized.

Dated: July 6, 2026

CLEARSIGN TECHNOLOGIES CORPORATION

By:

/s/ Colin James Deller

Name:

Colin James Deller

Title:

Chief Executive Officer

EX-5.1 — EXHIBIT 5.1

EX-5.1

Filename: tm2619440d1_ex5-1.htm · Sequence: 2

Exhibit 5.1

July 6, 2026

ClearSign Technologies Corporation

8023 East 63rd Place, Suite 101

Tulsa, Oklahoma 74133

Re:

ClearSign Technologies Corporation – Registration Statement on Form S-3 (File No. 333-288736)

Ladies and Gentlemen:

We have acted as counsel

to ClearSign Technologies Corporation, a Delaware corporation (the “Company”), in connection with its filing of

(i) a Registration Statement on Form S-3 (File No. 333-288736) (the “Registration Statement”)

under the Securities Act of 1933, as amended (the “Act”), with the Securities and Exchange Commission (the

“Commission”), (ii) the base prospectus, dated as of July 28, 2025 (the “Base

Prospectus”), included in the Registration Statement and (iii) the prospectus supplement to the Base Prospectus,

dated as of July 6, 2026 (together with the Base Prospectus, as supplemented from time to time by one or more prospectus

supplements, the “Prospectus”), filed with the Commission by the Company pursuant to Rule 424 promulgated

under the Act.

The Prospectus relates to

the public offering of an aggregate of $6,875,000 of shares of common stock, par value $0.0001 per share (the “Shares”).

The Shares are being sold pursuant to that certain At the Market Offering Agreement, dated as of July 17, 2025, by and between H.C.

Wainwright & Co., LLC, as the sales agent, and the Company (the “Offering Agreement”). This opinion is being

furnished in connection with the requirements of Item 601(b)(5) of Regulation S-K under the Act, and no opinion is expressed herein

as to any matter pertaining to the contents of the Registration Statement or the Prospectus, other than as expressly stated herein with

respect to the issuance of the Shares.

We have examined such matters

of fact and questions of law as we have considered appropriate for purposes of this letter. With your consent, we have relied upon certificates

and other assurances of officers of the Company and others as to factual matters without having independently verified such factual matters.

The opinions expressed herein are limited to the General Corporation Law of the State of Delaware. We express no opinion as to the effect

on the matters covered by this letter of the laws of any other jurisdiction. We express no opinion herein concerning any state securities

or blue sky laws.

In our examination of the

foregoing documents, we have assumed the genuineness of all signatures, the authenticity of all documents submitted to us as originals,

the conformity to original documents of all documents submitted to us as copies, the authenticity of the originals of such latter documents

and the legal competence of all signatories to such documents.

437

Madison Ave., 25th Floor, New York, New York 10022-7001

Phone: (212) 509-3900 Fax: (212) 509-7239 Website: www.msk.com

July 6, 2026

Page 2

Based upon the foregoing,

and subject to the assumptions, exceptions, qualifications and limitations set forth herein, we are of the opinion that the Shares have

been duly authorized for issuance, and when issued against payment therefor pursuant to the terms of the Offering Agreement, will be

validly issued, fully paid and non-assessable.

Please note that we are opining

only as to the matters expressly set forth herein, and no opinion should be inferred as to any other matters. This opinion is based upon

currently existing statutes, rules, regulations and judicial decisions, as further limited above, and we disclaim any obligation to advise

you of any change in any of these sources of law or subsequent legal or factual developments which might affect any matters or opinions

set forth herein.

This opinion is rendered to

you in connection with the offering described above.

We hereby consent to the filing

of this opinion with the Commission as an exhibit to the Current Report on Form 8-K of the Company being filed on the date hereof

and to the reference to our firm in the Prospectus and the Registration Statement. In giving such consent, we do not hereby admit that

we are in the category of persons whose consent is required under Section 7 of the Act or the rules and regulations of the Commission

thereunder.

Very truly yours,

/s/ Mitchell Silberberg & Knupp

LLP

Mitchell Silberberg & Knupp

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