The past month or so, I have the impression that Codex started hitting the 5h limits much more often. I always used the latest model in xhigh, but would almost never hit any limit (I'm not a very heavy user).

Lately, after 5.5 I've been hitting the 5h limit almost daily.

Did they change something?

I just stumbled onto this, which probably explains it: https://openrouter.ai/announcements/gpt55-cost-analysis