Amendment to Annual Report (Form 10-K/A)

This Amendment No. 1 on Form ("Amendment No. 1") amends the Annual Report of CSG Systems International, Inc. ("CSG", the "Company" or forms of the pronoun "we") on Form for the fiscal year ended December 31, 2025, as filed with the Securities and Exchange Commission (the "SEC") on February 19, 2026 (the "Original Filing").

We are filing this Amendment No. 1 to amend and restate in their entirety Part III, Item 10 (Directors, Executive Officers and Corporate Governance), Item 11 (Executive Compensation), Item 12 (Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters), Item 13 (Certain Relationships and Related Transactions, and Director Independence), and Item 14 (Principal Accountant Fees and Services) of Form that were previously omitted from the Original Filing in reliance on General Instruction G(3) to Form because a definitive proxy statement containing such information will not be filed within 120 days after the end of the fiscal year covered by the Original Filing.

In addition, Item 15 of Part IV has been amended solely to include new certifications by our principal executive officer and principal financial officer pursuant to Section 302 of the Sarbanes-Oxley Act of 2002. The certifications of our principal executive officer and principal financial officer are filed with this Amendment No. 1 as Exhibits 31.01 and 31.02 hereto. Because no financial statements have been included in this Amendment No. 1 and this Amendment No. 1 does not contain or amend any disclosure with respect to Items 307 and 308 of Regulation paragraphs 3, 4, and 5 of the certifications have been omitted. Additionally, we are not including the certification under Section 906 of the Sarbanes-Oxley Act of 2002 as no financial statements are being filed with this Amendment No. 1.

Except as described above, no other changes have been made to the Original Filing. Other than the information specifically amended and restated herein, we have not updated the information contained herein for events occurring subsequent to the filing date of the Original Filing. This Amendment No. 1 should be read in conjunction with the Original Filing and the Company's other filings made with the SEC subsequent to the filing of the Original Filing. Capitalized terms used herein and not otherwise defined are defined as set forth in the Original Filing.