OpenAI Retires GPT-4.5 — The GPT-4 Era Is Over

OpenAI has retired GPT-4.5 from ChatGPT, quietly closing the book on the GPT-4 model generation. The retirement took effect on June 27, 2026, after a 30-day sunset period announced in late May. GPT-4.5 was the last remaining model from the GPT-4 family available in ChatGPT.

What Changed

If you had GPT-4.5 selected as your model in ChatGPT, it has now been switched to GPT-5.5 automatically. Existing conversations that used GPT-4.5 continue to work — they simply run on the newer model going forward. No action is needed from users.

Custom GPTs that were built on GPT-4.5 have also been migrated. OpenAI says the transition should be seamless for most use cases, since GPT-5.5 matches or exceeds GPT-4.5 across all major benchmarks.

The o3 reasoning model is next. OpenAI has confirmed that o3 will be retired from ChatGPT on August 26, 2026, following a 90-day sunset period.

Why It Matters

GPT-4.5 was a significant model in OpenAI’s history. Released as the final entry in the GPT-4 generation, it was known for being particularly strong at creative writing and nuanced conversation — qualities that earned it a loyal following among paid subscribers. Some users have noted that GPT-5.5, while more capable overall, has a slightly different tone and style.

The retirement is part of OpenAI’s broader strategy to consolidate around its GPT-5.x model family. With GPT-5.6 Sol, Terra, and Luna now in limited preview, keeping older models running adds infrastructure cost with diminishing returns.

Importantly, the API is unaffected. Developers who rely on GPT-4.5 for production applications can continue using it through the API without any changes.

What This Means for You

If you are a ChatGPT user, the switch has already happened — there is nothing you need to do. GPT-5.5 is a more capable model, and most people will notice improved performance on tasks like coding, analysis, and research.

If you relied on GPT-4.5 for its specific writing style or behaviour, you may want to adjust your prompts to get similar results from GPT-5.5. The models handle instructions slightly differently, so some fine-tuning of your approach may help.

For developers building on the API, there is no urgency. But OpenAI’s pattern is clear: models eventually move from ChatGPT retirement to API deprecation. If you are still running production workloads on GPT-4.5, it is worth planning a migration to the GPT-5.x family sooner rather than later.

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