OnePlus founder and CEO Pete Lau has confirmed this on Twitter but, because Android O is not official yet, there is no estimate as to how long it will be take before it is available for the two flagships.
This is actually a welcome improvement because the way that OnePlus handled major software updates previously meant that owners of the previous flagship couldn’t count on their device getting a new version of Android. Case in point: while the OnePlus 3T and OnePlus 3 got Android 7 Nougat in late-December, the OnePlus 2 has yet to receive the same treatment.
It is possible that the OnePlus 3T and OnePlus 3 will be upgraded to Android O at the same time as the OnePlus 5. It could take a few months for the OnePlus 5 to get Android O, and then a few more months for it to be available for the OnePlus 3T and OnePlus 3. A (pessimistic) estimate would put the release date sometime in early-2018.
