United States securities and exchange commission logo July 8, 2021 John Stark Chief Executive Officer Quantum-Si Incorporated 530 Old Whitfield Street Guilford, Connecticut 06437 Re: Quantum-Si Incorporated Registration Statement on Form S-1 Filed July 2, 2021 File No. 333-257676 Dear Mr. Stark: This is to advise you that we have not reviewed and will not review your registration statement. Please refer to Rules 460 and 461 regarding requests for acceleration. We remind you that the company and its management are responsible for the accuracy and adequacy of their disclosures, notwithstanding any review, comments, action or absence of action by the staff. Please contact Alan Campbell at 202-551-4224 with any questions. Sincerely, Division of Corporation Finance Office of Life Sciences