# EDGAR Filing Document

**Accession Number:** 0001434524
**File Stem:** 0001104659-26-075734
**Filing Date:** 2026-6
**Character Count:** 6198
**Document Hash:** de1c5d04266db214d6ccb87dfd5bd025
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001104659-26-075734.hdr.sgml**: 20260618

**ACCESSION NUMBER**: 0001104659-26-075734

**CONFORMED SUBMISSION TYPE**: 8-K

**PUBLIC DOCUMENT COUNT**: 11

**CONFORMED PERIOD OF REPORT**: 20260618

**ITEM INFORMATION**: Other Events

**ITEM INFORMATION**: Financial Statements and Exhibits

**FILED AS OF DATE**: 20260618

**DATE AS OF CHANGE**: 20260618

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** ClearSign Technologies Corp
- **CENTRAL INDEX KEY:** 0001434524
- **STANDARD INDUSTRIAL CLASSIFICATION:** INDUSTRIAL INSTRUMENTS FOR MEASUREMENT, DISPLAY, AND CONTROL [3823]
- **ORGANIZATION NAME:** 08 Industrial Applications and Services
- **EIN:** 000000000
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** 8-K
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-35521
- **FILM NUMBER:** 261102751

**BUSINESS ADDRESS:**
- **STREET 1:** 8023 E. 63RD PLACE, SUITE 101
- **CITY:** TULSA
- **STATE:** OK
- **ZIP:** 74133
- **BUSINESS PHONE:** (918) 500-7312

**MAIL ADDRESS:**
- **STREET 1:** 8023 E. 63RD PLACE, SUITE 101
- **CITY:** TULSA
- **STATE:** OK
- **ZIP:** 74133

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** CLEARSIGN COMBUSTION CORP
- **DATE OF NAME CHANGE:** 20080507

?xml version='1.0' encoding='ASCII'?

**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): June 18, 2026**

**CLEARSIGN TECHNOLOGIES CORPORATION**

**(Exact name of registrant as specified in charter)**

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| | | |
|:---|:---|:---|
| **Delaware** | **001-35521** | **26-2056298** |
| **(State or other jurisdiction of <br> incorporation)** | **(Commission File Number)** | **(IRS Employer <br> Identification No.)** |

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**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:

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| | | |
|:---|:---|:---|
| **Title of each class** | **Trading Symbol(s)** | **Name of each exchange on which <br> 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. ◻

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| | |
|:---|:---|
| **Item 8.01** | **Other Events.** |

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As previously disclosed in a Current Report on Form 8-K filed with the Securities and Exchange Commission ("SEC") on June 1, 2026, ClearSign Technologies Corporation (the "Company") entered into an underwriting agreement, dated May 28, 2026 (the "Underwriting Agreement"), with Newbridge Securities Corporation (the "Underwriter"), relating to the Company's firm-commitment underwritten public offering (the "Offering") for the issuance and sale of 777,780 shares (the "Firm Shares") of the Company's common stock, par value $0.0001 per share (the "Common Stock"), primarily to existing stockholders of the Company, at a public offering price of $4.33 per Firm Share, less underwriting discounts and commissions, pursuant to an effective registration statement on Form S-3 (File No. 333-288736) (the "Registration Statement"), including the prospectus forming a part of the Registration Statement, as supplemented by a preliminary prospectus supplement, dated May 28, 2026, and a final prospectus supplement, dated May 28, 2026, each filed with the SEC. Under the terms of the Underwriting Agreement, the Company also granted the Underwriter an option exercisable for thirty (30) days (the "Over-allotment Option") to purchase up to an additional 116,667 shares of Common Stock (the "Additional Shares") from the Company at the Firm Share price, less underwriting discounts and commissions, to cover over-allotments. The Offering closed on June 1, 2026.

On June 18, 2026, pursuant to the full exercise of the Over-allotment Option, the Underwriter purchased 116,667 Additional Shares, for net proceeds of approximately $470,858 after deducting underwriting discounts and commissions and estimated expenses payable by the Company. The Company intends to use the net proceeds from the offer and sale of the Additional Shares for working capital, research and development, marketing and sales, and general corporate purposes.

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| | |
|:---|:---|
| **Item 9.01** | **Financial Statements and Exhibits.** |

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**(d) Exhibits.**

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| | |
|:---|:---|
| **Exhibit No.** | **Description** |
| 104 | Cover Page Interactive Data File (embedded within the Inline XBRL document). |

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**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: June 18, 2026

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| | |
|:---|:---|
| **CLEARSIGN TECHNOLOGIES CORPORATION** | **CLEARSIGN TECHNOLOGIES CORPORATION** |
| By: | /s/ Colin James Deller |
| Name: | Colin James Deller |
| Title: | Chief Executive Officer |

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