OpenAI will completely shut down the fine-tuning API: large models fully shift to prompts, startup teams lose underlying customization options

According to Beating Monitoring, OpenAI has sent an official email announcing the complete shutdown of its self-service fine-tuning service for developers. Starting immediately, new users can no longer create fine-tuning tasks; existing active users can only use the service until January 6, 2027. As for already deployed fine-tuned models, their inference services will be tied to the lifecycle of the underlying base models, and will cease once the base models are retired.

OpenAI’s main reason is that the next-generation base models (such as GPT-5.5) are already extremely powerful in following instructions and formatting. Compared to expensive fine-tuning, directly writing prompts combined with retrieval-augmented generation (RAG) is not only cheaper and faster but also sufficient to cover most scenarios.

Tech media Startup Fortune believes that this is not merely a product cleanup but a contraction of OpenAI’s underlying model interfaces. In the past, startups often used low-cost self-service fine-tuning to create customized products for vertical industries. With this channel closed, developers can only use general prompt engineering. This significantly increases the difficulty for startup teams to build customized technical barriers around the OpenAI ecosystem.