Context window versus usage window
People search "how to check Codex context window" when they are about to run out of something. Often they mean quota. Sometimes they mean the model really cannot see the rest of the file.
Context window: how much the model can attend to in this session. Usage window: how much of your plan is left before a reset. Mixing them up wastes a perfectly good afternoon of debugging the wrong limit.
Where to look
Context size lives with the model and the Codex session UI. UsageAtlas does not pretend to be that spec sheet.
For quota, run /status or open UsageAtlas. How to check Codex usage is the walkthrough for that path.
Questions, answered
Does UsageAtlas show the Codex context window size?
No. It shows usage windows, remaining capacity, tokens, and history. Context window size belongs to the model and the Codex UI.
Why did my Codex session feel 'full' if quota remains?
The context window can fill while weekly quota is still fine. Compact, start a new session, or check the model's context limit.
What does UsageAtlas show instead?
Session and weekly usage windows, tokens, credits where reported, and history.