And it's thanks to WordPress.
WordPress has long had an XML-RPC API that is enabled by default on every installation. It’s the very same XML RPC API that is used (and abused) to perform “pingbacks” whenever another WordPress installation links to you.
It’s a powerful thing, if used properly. And it’s about to get a baby sister in the form of a REST API:
REST API: Introduce baby API to the world.
Baby API was born at 2.8KLOC on October 8th at 2:30 UTC. API has lots of growing to do, so wish it the best of luck.
The new API is introduced in commit 34928. It’s target is the WordPress 4.4 release, which currently has no known launch date yet which is the current stable release.
From a personal standpoint, I much prefer REST API’s over RPC XML API’s. They’re much easier to integrate in simple scripts. That said, it is a matter of preference and I don’t create complex scenarios that use the API as a power user.
The new API will seemingly live in /wp-includes/rest-api.php, whereas the XML RPC one lived in the root directory at /xmlrpc.php.
From the 25% of the world sites (official numbers) that are about to get a REST API, I doubt anyone would even give two cents. But hey, if a giant like WordPress launches something new – it deserves some attention.