Google has released details of the Android O developer preview timeline, and it'll be familiar to those of you who participated last time around. The Android O DP will include four releases in advance of the final build. That is currently scheduled for Q3 of this year. So, probably another late fall launch for Android.
The system image we have today is the initial alpha release. In May or June, we should see a new preview image. That will be an incremental beta update. The next update about a month later will include all the final APIs and SDK. Developers will be able to publish apps in the Play Store for the new API level at that time. The last preview hits shortly before the final release this fall. It will be a near-final system image.
There's no beta program right now, but hopefully that will change when the next system image rolls out. For now it's flashing the old-fashioned way.
- Android Developers