OpenAI Caps Codex Context at 272k to Avoid High Cache-Read Costs
SquirrelMotor5379 · reddit · 2026-08-10
A developer discovered that OpenAI quietly limited the GPT-5.6 context window to 272,000 tokens in Codex, down from the stated 1,050,000. Coincidentally, 272k is the exact threshold where API billing doubles.
While the community suspected this was to prevent users from hitting massive bills, OpenAI stated the limit is due to the high cost of cache reads as context is shuffled back and forth between tool calls. The company plans to restore higher context windows in the future without resulting in higher usage charges.
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