YouTube have announced in their API blog that they are making a notable change to their YouTube API. The API, which returns results in both XML and JSON, is getting an upgrade on the JSON side, and the change is different enough that they are giving the format a new name JSON-C:
We've rethought out current JSON implementation, and moved away from a literal representation of the Atom data to a format that we hope will be more pleasing to those who are fluent in JSON. The vestigial XML namespace prefixes are no more, and we've removed many pieces of metadata specific to Atom documents that come across as noise in JSON. Repeating data elements are always structured as true JSON lists, and useful video metadata that exist as XML attributes in Atom have been rearranged to make more sense in the JSON document. You'll also find that the new JSON results are more compact than Atom XML, which is of special importance to code running from limited-bandwith mobile applications.
This change now makes the old JSON format depreciated. According to the Terms of Service, YouTube will continue to support the old JSON format for 3 years, but there will be no additional features features added. YouTube are encouraging developers to upgrade any existing code that is affected by the change.
If you want to get a sense of just how important JSON has become in the world of open APIs, keep in mind that over 450 APIs support JSON, some of whom support JSON exclusively.