Mistral Opens a Responses API in Public Preview That Uses OpenAI's Format and Keeps No Conversation State
Mistral released a Responses API in public preview on October 28 for building agents on its hosted chat models, including Mistral Large 4. Its documentation says the API uses the OpenAI Responses format and returns the model's answer, reasoning and function calls as separate output items. It is stateless: the developer's application keeps the conversation history and resends it with each request. Function calling in the preview covers functions the client runs itself.
Mistral's new API is designed so that developers do not have to give up OpenAI's request format to move to Mistral. The company's documentation says the Responses API "lets you build with Mistral models using the OpenAI Responses format," and that it works for new applications or for "bringing an existing Responses integration to Mistral." Crypto Briefing's write-up of the launch frames the main effect as lower switching costs for developers already using that format.
What is in the preview#
Mistral announced the Responses API in public preview on Wednesday, saying each response returns the model's answer, its reasoning and its tool calls as separate items, and that it works with all chat models hosted by Mistral, including Large 4. The documentation lists text input and output, image and file input, structured output in JSON mode and JSON Schema, streaming, reasoning effort settings depending on the model, and an endpoint for counting input tokens. Function calling in the preview covers client-executed functions, meaning the developer's own code runs the tool and returns the result.
The API is stateless, according to the documentation: the application keeps the conversation history and sends it with each request, including output items from earlier responses. Mistral's code examples use mistral-large-4, the model Mistral put on a paid preview API earlier this month.
Limits#
- This is a preview, and Mistral's documentation asks users to report issues to its support team; features and behaviour may change.
- Mistral's post says the API makes each step easier to handle than Chat Completions; that is the company's claim, and we have not tested it.
- The preview page does not give separate pricing for the Responses API, and we did not find a Mistral pricing announcement for it.
Sources#
- Mistral Docs: Responses API (preview)
- Mistral AI on X: Responses API public preview announcement (October 28, 2026)
- Crypto Briefing: Mistral opens Responses API in public preview, borrowing OpenAI's format for agent builders (October 28, 2026)
- Times of AI: Mistral Puts 1T-Parameter Large 4 on a Paid Preview API (October 6, 2026)