OnePlus has now started rolling out the stable update to OxygenOS 16 based on Android 16 to the OnePlus 12. The rollout is starting with units purchased in India, and OnePlus promises it will reach more regions soon.
An open beta program has seemingly started, but you can't just get in. Instead, you need to pass an eligibility quiz. You reach this by going to Settings > System & update > Software Update then hitting the three dots and choosing Beta Program. This should work if you have a OnePlus 13, OnePlus 13R, OnePlus 13s, OnePlus Open, OnePlus 12, OnePlus 12R, Oppo Find X8, or Oppo Find X8 Pro.