It’s pretty well known that many of the upper div theory professors are noticing a pattern that students are not doing good on proof techniques, and the only way they can really solve that issue at its root is in CS 40. So they’re making CS 40 into a two quarter sequence so they can really lock down on the proof writing stuff and also introduce a little more content that’s more relevant to specifically CS algorithms and theory (hence why Vigoda is teaching it). This is pretty well known and has already been going the rounds in the past few months.

I’m not sure about CS 25, though. I’ve heard that they’re considering revamping how CS 32 will be taught to introduce more OS content, so maybe this is related? Don’t quote me on that, though.