OpenAI added a small but operationally important Codex deadline: 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.
This is not a blanket retirement. The changelog says GPT-5.4 and GPT-5.4 mini remain available on the OpenAI API and in Codex sessions authenticated with an API key. The affected surface is the ChatGPT-signed Codex path, which is exactly where workspace defaults, saved model choices, managed configurations, custom agents, and scheduled tasks can silently carry an old model selection.
The recommended replacements are explicit: replace gpt-5.4 with GPT-5.6 Terra, and replace gpt-5.4-mini with GPT-5.6 Luna.
The useful action is boring and immediate. Audit saved Codex defaults before August 31, especially any shared team config or scheduled task that does not get opened every day. A human choosing a model in the UI will notice a missing option. A saved agent configuration may only fail when work is already queued.
For New Runtime, this is another reminder that model routing is part of operations. A model name is not just a capability choice; it becomes config state, migration risk, and idempotency surface. The site already covered GPT-5.6 as API economics. This is the follow-through: after price-performance changes, the runtime still has to migrate old defaults without breaking stored workflows.