Organizations that want to get and reuse Crossref metadata can do this in a number of ways. Crossref offers a number of APIs that are free with no performance or service guarantees and certain restrictions. Organizations who need to retrieve a lot of metadata and use Crossref metadata in production services can become an Affiliate and pay for a query account.
Affiliates can use their account to access the XML query API and submit large batches of queries.
There are fees for the Affiliate query account.
If you are interested in signing up as an Affiliate then go to the application form.