Found at “Unrolling the Codex agent loop” on 2026-01-27T10:51:08+01:00.

You might be asking yourself, “Wait, isn’t the agent loop quadratic in terms of the amount of JSON sent to the Responses API over the course of the conversation?” And you would be right. While the Responses API does support an optional previous_response_id⁠ parameter to mitigate this issue, Codex does not use it today, primarily to keep requests fully stateless and to support Zero Data Retention (ZDR) configurations.