Most likely the security fix that was issued recently for 16, which explains the small size.
So far, the only fix I’ve noticed has been the accessibility option to use personal voice (the keyboard initially covered the prompt, now it’s back to normal).
I think the build number is different from the last beta 3.
Oh, so it is. I have a separate update. My bad!
Oh no, totally understandable. It’s strange for them to release two betas with the same number, so it’s confusing.