It is surprising that they missed this change, though. Given how core type hints are for their projects and how broadly publicised the changes and developments

It is surprising that they missed this change, though. Given how core type hints are for their projects and how broadly publicised the changes and developments in type hints were. I'd be surprised if there weren't any issues raised against their projects about those. It feels it'd be harder to miss it than it'd be to stumble upon it. Also, weird for them to forget that there is a change that will break the foundations of their libraries. You'd think they would have that in the back of their minds and, being stakeholders, even being part of the discussions. Like you said, it's FOSS and, most importantly, python is a community project.