codex ships with a model catalog, and its gpt-5.6 entry lists the context window as 272,000 tokens. the published spec for the model is 1,050,000. 272,000 is also where the api reprices: past that many input tokens the whole request bills at 2x input and 1.5x output, including the tokens under the line. the obvious read is that the window was set to keep sessions on the cheap side of it. that is not the reason openai gave. thibault sottiaux said the driver is "overall cost of cache reads going up with the size of the context being shuffled back and forth between toolcalls". an agent resends its context on every tool call, so a bigger window multiplies across a long session rather than costing once. he also said the plan is to go back higher without it resulting in higher usage being charged. i only went looking because a session started compacting a bit under 245k, which is ninety percent of 272k. i had been in verdent with eco mode on for the other half of that week and had not been watching a window fill at all. the part that stays with me is how it arrived. a number in model metadata, inside an ordinary release, no blog post and no changelog entry. the issue filed calling it a regression is closed. issue 34619, asking for the 372k window back or an opt-in setting, is still open, and part of what it asks for is that context window changes get published anywhere.   submitted by   /u/SquirrelMotor5379 [link]   [comments]