Function context_window_for_model 

pub fn context_window_for_model(model: &str) -> u64

Fable, Haiku 5.5+, Opus 5+ and Sonnet 5+ run a 1M window natively: JSONL strips the [1m] tag, yet 74 bare claude-opus-5*/claude-sonnet-5 sessions were observed sending requests over 200K. Opus/Sonnet 4.x stay 200K unless tagged [1m].