One of the rumored additions in Android Q Beta 5 was a dark boot screen on Pixel devices, which would address a common complaint that rebooting your phone at night flashes you with a bright light. The feature has made an appearance in the latest beta, but not for all devices.
Starting with Android Q Beta 5, the Pixel boot screen has now switched to a dark background, but the rest of the animation is identical. The boot sceen doesn’t seem to be affected by dark mode being on or off — it’s simply always dark (after the first reboot with Q, anyway).
The one annoying caveat is that, at least for now, the new background isn’t available on all Pixels. We couldn’t get it working on anything other than a Pixel 3/3XL, and our friends at 9to5Google are reporting the same. There doesn’t appear to be a technical reason why the earlier Pixels can’t have a dark boot animation, but perhaps they will in a later Q release.