GPT-5.4 Left ChatGPT-Signed-In Codex on August 31, 2026

OpenAI changed where GPT-5.4 and GPT-5.4 mini can be used. OpenAI said the models would no longer be available in Codex for users signed in with ChatGPT starting August 31, 2026, and that date has now passed. (ChatGPT and Codex changelog)

The change is specific to the ChatGPT sign-in path. OpenAI says both models remain available on the OpenAI API and in Codex sessions authenticated with an API key, and that half is independently checkable: on September 1, 2026, the day after the cutoff, both gpt-5.4 and gpt-5.4-mini still returned live serving endpoints from OpenAI and Azure. (ChatGPT and Codex changelog)

What is changing

(OpenAI Developers on X, ChatGPT and Codex changelog)

This is an access-path change, not a statement that the models are being shut down everywhere. The announcement does not say that the API models are being renamed, repriced, or retired on that date.

Who needs to pay attention

The change matters most if your Codex workflow uses ChatGPT account authentication and explicitly selects GPT-5.4 or GPT-5.4 mini. The cutoff has passed, so the check is now retrospective: audit those sessions and any saved model preferences to find where a pinned GPT-5.4 selection is now failing or silently falling back.

If your workflow already uses an API key, OpenAI's announcement says the models remain available through the API and API-key-authenticated Codex sessions. For ChatGPT-signed-in sessions, OpenAI's changelog entry recommends replacing gpt-5.4 with gpt-5.6-terra (GPT-5.6 Terra) and gpt-5.4-mini with gpt-5.6-luna (GPT-5.6 Luna), and says to update workspace defaults, saved model settings, managed configurations, custom agents, and scheduled tasks that use either model before the cutoff. (OpenAI Developers on X, ChatGPT and Codex changelog)

What the sources do and do not establish

OpenAI's announcement establishes the date, the two paths where the models remain available, and the recommended replacements (GPT-5.6 Terra for GPT-5.4, GPT-5.6 Luna for GPT-5.4 mini). It does not establish a new default model for ChatGPT-signed-in Codex sessions, whether existing settings will be migrated automatically, or whether usage limits will change.

Those three questions are still open after the cutoff. OpenAI published no follow-up entry, so the safe reading is unchanged: ChatGPT sign-in lost access in Codex on August 31, while API-key access remains supported according to the changelog and to the models' still-live serving endpoints. (ChatGPT and Codex changelog)

Update (September 1, 2026): the cutoff date has passed and OpenAI published nothing further. Re-checked the changelog the morning after. The July 31, 2026 entry is still live and still word-for-word what it was, headed "GPT-5.4 and GPT-5.4 mini retire from Codex on August 31" and reading: "On August 31, 2026, GPT-5.4 and GPT-5.4 mini will no longer be available in Codex for users signed in with ChatGPT." OpenAI has not rewritten it into the past tense, has not posted a confirmation entry, and has not announced an extension. The most recent entries on the changelog are Codex CLI 0.151.0 (August 29) and 0.152.0 (September 1), neither of which mentions GPT-5.4.

The API half of the announcement is independently confirmed: on September 1, 2026, gpt-5.4 and gpt-5.4-mini both still returned live serving endpoints from OpenAI and Azure, so the models were not withdrawn from the API alongside the Codex change. The ChatGPT-sign-in half cannot be verified from outside an account, so this page reports OpenAI's stated schedule rather than an observed outcome.

Update (August 30, 2026): Re-verified one day before the cutoff. OpenAI's changelog entry of July 31, 2026 is still live and unchanged, headed "GPT-5.4 and GPT-5.4 mini retire from Codex on August 31", and still reads: "On August 31, 2026, GPT-5.4 and GPT-5.4 mini will no longer be available in Codex for users signed in with ChatGPT. GPT-5.4 and GPT-5.4 mini will remain available on the OpenAI API and Codex sessions authenticated with an API key." OpenAI has published no extension, no new default model for ChatGPT-signed-in Codex sessions, and no migration statement, so the three open questions above are still open. Note the scope wording: the retirement is from Codex, not from the ChatGPT app.

Bottom line

GPT-5.4 and GPT-5.4 mini left ChatGPT-signed-in Codex sessions on August 31, 2026, per OpenAI's announced schedule, which OpenAI has neither extended nor amended. API users and Codex users authenticated with an API key were not included in the change, and both models were still being served on the API a day after the cutoff.

Sources

• OpenAI Developers announcement on X, July 31, 2026: https://x.com/OpenAIDevs/status/2083301245390143831
• ChatGPT and Codex changelog, July 31, 2026 entry: https://learn.chatgpt.com/docs/changelog#codex-2026-07-31 (durable vendor source; re-verified verbatim August 30, 2026, one day before the cutoff, and again September 1, 2026, the day after -- unchanged, still in the future tense, with no follow-up entry and no extension. This entry carries every claim on this page; the X post above is corroboration, not the load-bearing citation.)
• OpenRouter model endpoint listings for openai/gpt-5.4 and openai/gpt-5.4-mini, checked September 1, 2026: both return non-empty endpoint sets served by OpenAI and Azure, which is the independent check that the models were not withdrawn from the API alongside the Codex sign-in change.