Cost Openness and Spending Transparency Act of 2023 or the COST Act of 2023 This bill requires recipients of federal funds to disclose financing information relating to programs, projects, or activities carried out using such funds. Specifically, such a recipient (including a state or local government or a recipient of a federal research grant) must clearly state in any press release, request for proposals, bid solicitation, or other document describing the activity the amount and percentage of federal funding and the amount and percentage of nongovernmental funding. An individual or entity carrying out a program, project, or activity that is carried out using federal funds must, as part of the performance progress reporting, include a certification indicating whether the individual or entity complied with the disclosure requirements. The Office of Management and Budget (OMB) must annually review a random sampling of public communications issued by agencies and recipients of federal funds for compliance with the disclosure requirements, and make publicly available the findings of the review. The OMB must make available to the public a mechanism to anonymously report communications that do not comply.