Earlier this week, the REST API team announced that it will be merged with core in 4.4, which is slated for release in a few months.
The API comes in two parts, infrastructure and endpoints. You can rejoice that the infrastructure is part of core and that the endpoints will be available in the plugin.
So what exactly does this mean?
For one, everyone can build RESTful APIs much easier, and therefore, makes building custom APIs for your site a breeze. Plugin and theme developers can begin building right now. Start replacing any code you already have including admin-ajax endpoints. The only way to authenticate using the API is by using built-in cookie authentication for now. The process is incredibly easy and there’s a guide to help you get started.
Unfortunately, you won’t get much use out of the API if you’re a client author, but the team is working on endpoints for a future release.
The posts notes that if you’ve installed beta 2.0, you’ll need to download beta 5. If you’re running on beta 1, you won’t run into problems immediately but it is a good idea to upgrade anyway.
As with any new rollout, there will be kinks, but the infrastructure can be maintained on Trac. If you see things you want to change, send them into GitHub and make this the best it can be.
You can also contact the team on the #core-restapi channel on Slack, or tune into their weekly meeting on Nov. 2 at 3 p.m. PST.