I just tried my integration tests against beta 7.0 (I jumped from beta 5.0), but I get this error in my error log when I try to upload a file:

PHP Fatal error: 
Call to undefined function wp_tempnam() in /var/www/html/testapp.com/wp-content/plugins/rest-api/lib/endpoints/class-wp-rest-attachments-controller.php on line 334

Endpoint responds with a blank 500 response.

I'm running Wordpress in a Docker container, so literally the only thing that changed was which ZIP file was being used to unpack the plugin. Test code is the same.

Is this release broken?