o1 seems to have some crazy context length / awareness going on compared to current 3.5 Sonnet from playing around it just now. I'm not having to 'remind' it of initial requirements etc nearly as much.
I gave it a try and o1 is better than I was expecting. In particular the writing style is a lot lighter on "GPTisms". It's not very willing to show you its thought process though, the summaries of it seem to skip a lot more than in the preview.