Exhibit 32.1

Certification of Principal Executive Officer

Pursuant to 18 U.S.C. Section 1350, as adopted pursuant to

Section 906 of the Sarbanes-Oxley Act of 2002

I, William Brock, Chief Executive Officer of ClearThink 1 Acquisition Corp., hereby certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that to my knowledge, the quarterly report on Form 10-Q for the period ending June 30, 2026 of ClearThink 1 Acquisition Corp. (the “Form 10-Q”) fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934 and the information contained in the Form 10-Q fairly presents, in all material respects, the financial condition and results of operations of ClearThink 1 Acquisition Corp.