4.5a Beta 2 (v4.51.0.1906) will ship later this evening or early tomorrow.
To update to Beta 2 when it ships, use the Update Now command if you’ve switched to the beta channel before, or the Set Update Channel to Beta command if you’re on a stable version (such as 4.5 SR-2). To install Beta 2 from scratch, see the notes and download link on this thread.
Release Notes