Googler here, was SRE on tier 2 (not SRE anymore).
Tier 2 is still "proper" oncall and we were split between sites. I think devs would be tier 3 oncall instead which has no compensation and no expectation of a certain prompt response time (also SLAs and other metrics might be different since they usually aren't an SRE team). In that case tier 3 rotations wouldn't be handled by SREs and would likely not be split across sites (since dev teams aren't usually).
There may be exceptions, and I've never been in a dev team myself although I interacted with many so I might be wrong, but I can't recall ever seeing a tier 2 oncall SRE team not having a site split and having people 24/7 oncall overnight. Just my personal experience.
My team (SWE) does a week-long tier 2 oncall shift ~every 6 weeks. It's very disruptive to my life (although it doesn't seem to bother people without young kids or with stay-at-home partners). I would flat out refuse a team with more frequent oncall, even if it were tier 3.
At least at 2016, when I left Google, my team was tier 2 with weekly rotation (but we were onboarding sre support at the time, so it might change to 8-hour rotation later).
Doesn’t this only apply to SRE rotations? The dev teams I know of are definitely oncall overnight.