Notes on the new 1m context window for Claude Sonnet 4: https://
simonwillison.net/2025/Aug/12/cl
aude-sonnet-4-1m/
… You need to send a beta header of context-1m-2025-08-07 and be on tier 4, which means you have purchased at least $400 in API credits
Claude Sonnet 4 1M Context Window Access Requirements
By
–
