OpenAI is shutting down four GPT-4 models from its API on January 14, 2027, according to a deprecation notice the company sent developers Wednesday. The retirement covers GPT-4o, GPT-4o mini, GPT-4.1, and GPT-4.1 mini, along with their dated snapshots and every fine-tuned model built on top of them. Developers have just three months to migrate production traffic to the recommended replacement, GPT-6 Luna, which handles reasoning and tool calls differently enough that swapping the model ID may be the easiest part of the migration.
GPT-4o launched on May 13, 2024, as OpenAI's flagship and built a following loyal enough to change the company's plans. When GPT-5 replaced it in August 2025, Reddit filled with complaints, and OpenAI brought it back for paying ChatGPT subscribers the very next day. That reprieve lasted until February 13, 2026, when GPT-4o and GPT-4.1 disappeared from ChatGPT. Both remained available through the API, but that access now is sunsetting. By then, OpenAI said just 0.1% of daily ChatGPT users were still choosing GPT-4o, although the model continued serving API requests for applications built around it. GPT-4.1 was a different kind of release, arriving on April 14, 2025, as an API-only family that skipped ChatGPT entirely and went straight after developers with stronger coding, better instruction following, room for up to a million tokens of context, and more reliable diff formats for anyone letting a model loose on large files.
According to OpenAI's migration guide, GPT-6 Luna defaults to medium reasoning effort but supports function calling through Chat Completions only with reasoning_effort=none. Combining reasoning and tool calls requires the Responses API. Kevin Weil, OpenAI's chief product officer, called them models "trained just for developers" during the launch livestream, and Sam Altman went on X to say developers "seem very happy" with them. The company recommends using its Docs skill in Codex to update API calls across a project, but those changes won't account for differences in model behavior.
The three-month warning falls short of OpenAI's own deprecation policy, which promises at least six months' notice for generally available models. The policy allows exceptions for safety or compliance reasons, but there's no explanation for why GPT-4o and GPT-4.1 are getting only half that time. Luna is the fastest and cheapest tier of GPT-6, and on paper it covers the basics GPT-4.1 offered, with a 1.05 million-token context window, structured outputs and function calling. At $0.10 per million input tokens and $0.50 per million output tokens, it's cheaper than GPT-5.6 Luna, which charged twice as much for input and $1.20 per million output tokens. Once a prompt passes 272,000 input tokens, the input rate doubles and the output rate raises by 50% for the entire request. That could eat into the savings for RAG pipelines and coding agents working with large codebases. New self-serve fine-tuning jobs end on January 6, 2027, eight days before the GPT-4 models retire. Existing fine-tuned models will continue serving inference requests until January 14, leaving a short window to run replacements alongside them. Customers who need more time may be able to keep older models running through dedicated capacity, although they'll have to arrange that with OpenAI's sales team. The abbreviated timeline puts pressure on engineering teams already managing complex dependencies, while the architectural differences between model generations may force wider rewrites than the migration path suggests.