Today the first official version of the REST API of Visual Studio Online has been released, the version 1.0.
Announced in May as preview, now these APIs have reached a great maturity. This doesn't mean that they are done with the APIs completely but rather that a core set are now complete and from here forward, they’ll be versioning them for backward compatibility so all the apps that use them don’t break every time they update them.
Together with this announce, they have updated the "API Reference portal" and the "Getting started guide".
If you have existing apps using the 1.0 preview APIs, you should start migrating to the release 1.0 APIs as soon as possible. Graduated preview APIs (any API in the 1.0 set) are subject to stop working in 12 weeks from today. To learn more about versioning and migrating, see the "versioning and migration page".
That said, remember that, starting from today, the Visual Studio Online REST APIs follow this pattern: