Microsoft today released Windows 10 Insider Preview build 14390 for both PC and Mobile to the Fast ring.
As you may have guessed, there are no new front-facing features. The company is gearing up for an RTM build of the Windows 10 Anniversary Update. The public update is slated to start rolling out on August 2; however, Insiders should see an RTM build before that.
The only feature that the firm mentioned was the Amazon Assistant extension for Microsoft Edge, which was announced a couple days ago.
Amazon Assistant: Amazon’s official browser extension is now available for Microsoft Edge! Amazon Assistant helps you make better decisions wherever you shop online by giving you access to Deal of the Day, Product Comparison, Wish List and Shortcuts to your favorite Amazon destinations. Check out all of the available extensions by launching Microsoft Edge, opening the “…”menu, selecting “Extensions” and then clicking “Get extensions from the Store”.”
It's still safe to assume that this is not the RTM build, as there is still a small amount of known issues listed. Those will likely be fixed in time for the release.