Updates to PMC's ESearch and EPost E-utilities APIs Coming in Early February

PubMed Central (PMC) will be moving to updated versions of the ESearch and EPost E-utilities APIs in early February. These updated versions will use the same technology as the updated PMC website search which was released in September 2025. This means search results returned by the updated ESearch API will match those of the PMC website. If you manage code that creates PMC E-utilities requests, review the changes below to ensure that your code will continue to function after the update. This update only affects the ESearch and EPost E-utilities API calls with &db=pmc. There are no changes to the E-utilities for other databases. The current E-utilities URLs for PMC ( &db=pmc ) will continue to function after the update is released, with only a few exceptions: ESearch will only be able to access the first 10,000 records retrieved by the search query ( &retmax <= 10,000; &retstart + &retmax <= 10,000 ). EPost will only be able to accept up to 10,000 PMCIDs in a single URL request. ESearch will return exactly the same PMCIDs as those returned by a PMC website search. Please note that PMC's eFetch output formats were updated in April 2025.