COGENT COMMUNICATIONS HOLDINGS, INC. 10-Q

ITEM 5. OTHER INFORMATION On May 20, 2026 , Thaddeus Weed , the Company’s Vice President and Chief Financial Officer , adopted a 10b5-1 trading plan for the sale of the Company’s common stock (a “Rule 10b5-1 Trading Plan”) that is intended to satisfy the affirmative defense conditions of Securities Exchange Act Rule 10b5-1(c). Mr. Weed’s Rule 10b5-1 Trading Plan provides for the sale of up to 36,468 shares pursuant to the terms of the plan, subject to certain conditions. The duration of this trading plan is 244 days . ​ Page 53 of 55 Table of Contents ITEM 6. EXHIBITS . (a) Exhibits Exhibit Number ​ ​ ​ Description 4.1 ​ First Supplemental Indenture, dated as of June 15, 2026, among Cogent Communications Group, LLC, Cogent Finance, Inc., the guarantors named therein and Wilmington Trust, National Association, as trustee and collateral agent (previously filed as Exhibit 4.1 to our Current Report on Form 8-K, filed on June 15, 2026, and incorporated herein by reference). 10.1 ​ Restricted Stock Agreement, dated as of May 4, 2026, between the Company and David Schaeffer (previously filed as Exhibit 10.2 to our Current Report on Form 8-K, filed on May 4, 2026, and incorporated herein by reference). 10.2* ​ Purchase and Sale Agreement, dated May 22, 2026 (previously filed as Exhibit 10.1 to our Current Report on Form 8-K, filed on May 26, 2026, and incorporated herein by reference). 10.3 ​ Third Amended and Restated Cogent Communications Holdings, Inc. 2017 Incentive Award Plan (incorporated by reference to Annex A of the Company’s Definitive Proxy Statement on Schedule 14A filed March 20, 2026 (File No. 000-51829)). 31.1 ​ Certification of Chief Executive Officer (filed herewith) 31.2 ​ Certification of Chief Financial Officer (filed herewith) 32.1 ​ Certification of Chief Executive Officer (furnished herewith) 32.2 ​ Certification of Chief Financial Officer (furnished herewith) 101.1 ​ The following materials from the Company’s Quarterly Report on Form 10-Q for the quarter ended June 30, 2026, formatted in Inline Extensible Business Reporting Language (XBRL), include: (i) the Condensed Consolidated Statements of Comprehensive Income (Loss), (ii) the Condensed Consolidated Balance Sheets, (iii) the Condensed Consolidated Statements of Cash Flows, and (iv) related notes (filed herewith). 104 ​ Cover Page Interactive Data File (the cover page XBRL tags are embedded within the iXBRL document). *Certain schedules and exhibits to this exhibit have been omitted pursuant to Item 601(a)(5) and Item 601(b)(10)(iv) of Regulation S-K. The Company agrees to provide a copy of any omitted schedule or exhibit to the SEC or its staff upon request. ​ ​ Page 54 of 55 Table of Contents SIGNATURES 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 thereunto duly authorized. ​ ​ ​ Date: August 6, 2026 COGENT COMMUNICATIONS HOLDINGS, INC. ​ ​ ​ By: /s/ David Schaeffer ​ ​ Name: David Schaeffer ​ ​ Title: Chief Executive Officer ​ ​ ​ Date: August 6, 2026 By: /s/ Thaddeus G. Weed ​ ​ Name: Thaddeus G. Weed ​ ​ Title: Chief Financial Officer and Treasurer ​ ​ ​ Page 55 of 55