What's the differences between the REST API and the Action API? I am mostly familiar with the Action API. Why are there two? Do they use the same actions? Is there a Special:ApiSandbox for the REST API? Is the REST API part of core and is turned on by default? Thanks.
Topic on API talk:REST API
Core_Platform_Team/Initiatives/Core_REST_API_in_MediaWiki and subpages/linked phab tasks might explain some of this.
> Is there a Special:ApiSandbox for the REST API?
See task T221742
> Is the REST API part of core and is turned on by default?
Yes, and yes.