alt Hacker Newshave been on 1M context window with claude since 4.0 - it gets pretty expensive when you run 1M context on a long running project (mostly using it in cline for coding). I think they've realized more context length = more $ when dealing with most agentic coding workflows on api.
You should be doing everything you can to keep context under 200k, ideally even 100k. All the models unwind so badly as context grows.