Entry into a Material Definitive Agreement. On May 14, 2026, CSG and U.S. Bank Trust Company, National Association as trustee (the “Convertible Notes Trustee”), entered into a Supplemental Indenture (the “Supplemental Indenture”), dated as of May 14, 2026, which supplements the Indenture, dated as of September 11, 2023 (the “Initial Indenture” and, together with the Supplemental Indenture, the “Indenture”), by and between CSG and the Convertible Notes Trustee, governing CSG’s 3.875% Convertib…

by reference. At the Effective Time, the former holders of shares of CSG Common Stock that were outstanding immediately prior to the Effective Time ceased to have any rights with respect to such shares, other than (in the case of shares of CSG Common Stock that were not Excluded Shares) the right to receive the Merger Consideration to be paid pursuant to the Merger Agreement.

by reference. On the terms and subject to the conditions set forth in the Merger Agreement, at the effective time of the Merger (the “Effective Time”), and as a result of the Merger, each share of common stock of CSG (“CSG Common Stock”) that was issued and outstanding immediately prior to the Effective Time (other than (i) shares of CSG Common Stock owned by CSG (as treasury stock or otherwise, and other than shares held on behalf of third parties) or owned by Parent or Merger Sub or any dir…

President and CEO, Director, CFO, EVP & CCO, EVP & CXO — Rachel Barger, David Barnes, Greg Conley, Marwan Fawaz, Samantha Greenberg, Rajan Naik, Brian Shepherd, Haiyan Song, Silvio Tavares, Lily Yang, Elizabeth A. Bauer, Rasmani Bhattacharya, Hai Tran: The resignation and termination of multiple senior executives due to the Merger Agreement.

The consummation of the Merger constitutes a Make-Whole Fundamental Change (as defined in the Initial Indenture). The effective date of such Make-Whole Fundamental Change is May 14, 2026, the date of the consummation of the Merger. Accordingly, following the Merger, each Holder has the right to convert its Convertible Notes into $80.70 in cash (without interest) in respect of each share of CSG Common Stock into which the Convertible Notes would have otherwise been convertible, and for any con…

by reference. In connection with the closing of the Merger, on May 9, 2026, CSG notified the Nasdaq Stock Market (“Nasdaq”) of the anticipated completion of the Merger and on May 11, 2026, CSG requested that Nasdaq (i) suspend trading of CSG Common Stock on Nasdaq before the opening of trading on May 14, 2026 and (ii) file a notification of removal from listing on Form 25 with the SEC to delist CSG Common Stock from Nasdaq and deregister CSG Common Stock under Section 12(b) of the Securities…

by reference. In connection with the consummation of the Merger, on May 14, 2026, all outstanding indebtedness and other amounts outstanding and owed under that certain Credit Agreement (the “Existing Credit Agreement”), dated as of March 14, 2025, by and among CSG, as borrower, its subsidiary guarantors party thereto, Royal Bank of Canada, as administrative agent, collateral agent, swingline lender and an issuing bank (“RBC”), Citizens Bank, N.A. and PNC Bank, National Association, as co-doc…

by reference. At the Effective Time, a change of control of CSG occurred. Merger Sub merged with and into CSG, the separate corporate existence of Merger Sub ceased, and CSG continued as the Surviving Corporation in the Merger as a wholly owned subsidiary of Parent.

Other Events. As previously disclosed, on October 29, 2025, CSG Systems International, Inc., a Delaware corporation (the “Company”), entered into an Agreement and Plan of Merger (the “Merger Agreement”), dated as October 29, 2025, with NEC Corporation, a company incorporated under the laws of Japan (“Parent”), and Canvas Transaction Company, Inc., a Delaware corporation and a wholly owned subsidiary of Parent (“Merger Sub”), pursuant to which, on the terms and subject to the conditions set fo…

Results of Operations and Financial Condition. The following information is furnished pursuant to Item 2.02 (Results of Operations and Financial Condition). This information shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or incorporated in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific reference in such a filing. On May 6, 2026, CSG…

Results of Operations and Financial Condition. The following information is furnished pursuant to Item 2.02 (Results of Operations and Financial Condition). This information shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or incorporated in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific reference in such a filing. The full text of CS…

Results of Operations and Financial Condition. The following information is furnished pursuant to Item 2.02 (Results of Operations and Financial Condition). This information shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or incorporated in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific reference in such a filing. On February 4, 2026…

Other Events. As previously disclosed, on October 29, 2025, CSG Systems International, Inc., a Delaware corporation (the “Company”), entered into an Agreement and Plan of Merger (the “Merger Agreement”), dated as October 29, 2025, with NEC Corporation, a company incorporated under the laws of Japan (“Parent”), and Canvas Transaction Company, Inc., a Delaware corporation and a wholly owned subsidiary of Parent (“Merger Sub”), pursuant to which, on the terms and subject to the conditions set fo…

Results of Operations and Financial Condition. The following information is furnished pursuant to Item 2.02 (Results of Operations and Financial Condition). This information shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or incorporated in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific reference in such a filing. On November 5, 2025…

Entry into a Material Definitive Agreement. On October 29, 2025, CSG Systems International, Inc, a Delaware corporation (the “Company”), NEC Corporation, a company incorporated under the laws of Japan (“Parent”), and Canvas Transaction Company, Inc., a Delaware corporation and a wholly owned subsidiary of Parent (“Merger Sub”), entered into an Agreement and Plan of Merger (the “Merger Agreement”), pursuant to which, on the terms and subject to the conditions set forth in the Merger Agreement,…

Entry into a Material Definitive Agreement. Summary of Material Definitive Agreement. CSG Systems International, Inc. (“CSG”) is a party to a Master Subscriber Management System Agreement, dated August 1, 2017 (the “Current Agreement”) with Charter Communications Operating, LLC (“Charter”). The Current Agreement is scheduled to expire on March 31, 2028. For the second quarter ended June 30, 2025, CSG generated approximately 19% of its total revenue from Charter. On September 4, 2025, CSG ente…

Results of Operations and Financial Condition. The following information is furnished pursuant to Item 2.02 (Results of Operations and Financial Condition). This information shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or incorporated in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific reference in such a filing. On August 6, 2025,…

Results of Operations and Financial Condition. The following information is furnished pursuant to Item 2.02 (Results of Operations and Financial Condition). This information shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or incorporated in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific reference in such a filing. On May 7, 2025, CSG…

1 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 hereunto duly authorized. CSG SYSTEMS INTERNATIONAL, INC. Date: March 18, 2025 By: /s/ Lori J. Szwanek Lori J. Szwanek Chief Accounting Officer

Entry into a Material Definitive Agreement. On March 14, 2025, CSG Systems International, Inc. (“CSG”) and certain of its subsidiaries entered into a new $600.0 million five-year debt arrangement with Royal Bank of Canada (“RBC”) acting as Administrative Agent, Collateral Agent, Swingline Lender, and an Issuing Bank; Citizens Bank, N.A. and PNC Bank, National Association, as Co-Documentation Agents; and RBC, HSBC Bank USA, National Association, U.S. Bank National Association, and Wells Fargo…

Termination of a Material Definitive Agreement. The information set forth above under

Results of Operations and Financial Condition. The following information is furnished pursuant to Item 2.02 (Results of Operations and Financial Condition). This information shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or incorporated in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific reference in such a filing. On February 5, 2025…

CEO — Brian A. Shepherd: The filing discloses a performance-based equity award to the sitting CEO, which is a compensatory arrangement rather than a departure or appointment event.

Results of Operations and Financial Condition. The following information is furnished pursuant to Item 2.02 (Results of Operations and Financial Condition). This information shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or incorporated in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific reference in such a filing. On November 6, 2024…

Entry into a Material Definitive Agreement. Summary of Material Definitive Agreement. CSG Systems International, Inc. (“CSG”) currently generates a material portion of its revenues from Comcast Cable Communications Management, LLC, an affiliate of Comcast Corporation (“Comcast”), under a multi-year Master Subscriber Management System Agreement (the “Current Agreement”). The Current Agreement is scheduled to expire on December 31, 2025. For the second quarter ended June 30, 2024, CSG generated…