Unpaywall is different to crossref. The size will be similar as a lot of scientific DOIs are from crossref, and they're a common dataset to base initial data on

Unpaywall is different to crossref. The size will be similar as a lot of scientific DOIs are from crossref, and they're a common dataset to base initial data on. https://unpaywall.org/data-format https://unpaywall.org/data-format is the format for unpaywall https://api.crossref.org/swagger-ui/index.html https://api.crossref.org/swagger-ui/index.html for crossref info