Data◆Article

Model performance degrades well before a context window is actually full, so usable context should be capped far below the stated maximum.

Dex's heuristic: push a 1M-token model to only 300-400K tokens, and smaller models to about 100K, before hitting a 'dumb zone' where the model starts making careless mistakes like deleting files. ✦ AI generated

Dex Horthy · The Pragmatic Engineer · 2026-07-15 · original ↗

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For a model with a 1M context window, Dex pushes it to around 300-400K when it feels right. For smaller models, he stops at around 100K. You hit the “dumb zone” when its performance starts to degrade because the context window fills up beyond this heuristic limit, and the model begins doing increasingly stupid things like deleting your .env file, for example.

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✳ context window

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