Google is expected to reach Android 16 platform stability this month. It is not surprising to see more Xiaomi phones testing the upcoming OS update. The latest to join the list is the Xiaomi 15, but only developers have access to the ROM.
Xiaomi will start organizing a public beta test for the Xiaomi 15 Android 15 build in the coming weeks, as the current build is for internal testing. This means the phone will be among the first to receive Android 16, which is not surprising. Remember, it debuted with Android 15, although Xiaomi 16 will be the first to run the new OS.
Details of Xiaomi 15 Android 15 beta update

Xiaomi has released the Android 16 build for its current flagship phone. Unfortunately, only developers have access to the OS2.0.250226.1. WOCMIXM build. From the version number, they are testing the new OS with HyperOS 2, but that will change before the final release.
We expect stable Android 16 to arrive with HyperOS 3. Perhaps the company has not started the development, as they are focused on the HyperOS 2.1 rollout. We hope to learn more in the coming weeks.
When is the stable Xiaomi 15 Android 16 update rolling out?
Last year, Xiaomi 15 debuted with Android 15, making it the first Xiaomi phone to run the OS at that time. Perhaps the company will repeat it with Xiaomi 16. If that is the case, we expect stable Android 15 to debut in October. Xiaomi 15 will probably get the upgrade during the last quarter of the year.
Of course, there might be a slight change this year. Google plans to release the stable Android 16 update in August. That is probably two months earlier compared to the Android 15 release. There is a chance we will see other smartphone makers release the update before October.