OpenAI adds 12 hour prompt caching to its API, and Tibo says Codex and Work now keep cache forever for logged in users
You can now choose 12-hour prompt caching in the API. Persistent agents, like dots, reuse context throughout the day. You can keep shared instructions, tools, and context cached longer and pay the lower cached-input rate, even when requests are hours apart.
Context
Longer caching cuts costs and wait times for agents that return to the same context hours later.
Prompt caching lets an API reuse work on a prompt's repeated beginning, such as instructions and tool definitions, at a lower price. Tibo leads Codex at OpenAI and posted the related Codex change as Day 16 of his run of daily updates.
Deep dive
On October 20, OpenAI Developers posted that developers can now choose 12 hour prompt caching in the API. It said persistent agents reuse context throughout the day, and that developers can keep shared instructions, tools and context cached longer and pay the lower cached input rate, even when requests are hours apart.
That evening, Tibo quoted the post as Day 16 of his run of updates. He said that besides the 12 hour API option, for logged in users across Codex and Work, OpenAI keeps the cache forever, so there is no penalty for coming back to an old conversation or resuming after a few hours, and users are now guaranteed to hit the cache.
Cached input is billed at a discount, so a longer window matters for agents that pause between steps or wait for people. Before this, cached prompts typically expired after a short period of inactivity, which meant a long pause could force the full price again. Neither post gave the exact cached price or said whether the 12 hour option costs extra.
Tibo's Day 12 update, covered October 16, had already mentioned longer caching in Codex and Work. The Day 16 post goes further with the claim of a permanent cache, which is OpenAI's own description and has not been tested independently.
What to expect next
Watch for OpenAI's pricing page to show whether 12 hour caching carries a storage charge, as some rivals charge for longer caches. Developers running long lived agents will show whether the savings are large in practice. Also watch whether Tibo's run of daily updates continues, and whether Anthropic and Google respond with longer caching of their own. For heavy Codex users, the permanent cache claim will be tested by whether usage drains more slowly when resuming old sessions.