On 13 October, we will be making backend changes to our content negotiation service, effectively folding it into our REST API. While behavior should be unchanged for requests made according to the specification, there are a few functional changes to note.
1) The resolver URL will change from http://data.crossref.org
2) Content negotiation responses will be returned by one of our three API pools depending on whether you include mailto identification in your user agent header for the polite pool, or include a token for Metadata Plus subscribers accessing the Plus pool. All other requests will be serviced by the public pool.