> For the complete documentation index, see [llms.txt](https://docs.fastrouter.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.fastrouter.ai/api-reference/responses.md).

# Responses

## Create Response

> Creates responses with conversation state management. Supports previous\_response\_id for context continuity, function calling, web search, and file inputs. Compatible with OpenAI, Azure, and X-AI (Grok) providers.

```json
{"openapi":"3.1.0","info":{"title":"FastRouter API Reference","version":"1.0.0"},"tags":[{"name":"Responses","description":"Alternative API for creating responses with built-in conversation state management."}],"servers":[{"url":"https://api.fastrouter.ai","description":"Production API"}],"security":[{"bearerAuth":[]}],"components":{"securitySchemes":{"bearerAuth":{"type":"http","scheme":"bearer","bearerFormat":"API Key","description":"FastRouter API Key. Get yours at https://fastrouter.ai\n\nFormat: `Authorization: Bearer YOUR_API_KEY`"}},"responses":{"UnauthorizedError":{"description":"Invalid Credentials - Your API key is invalid, missing, or disabled. Check your credentials.\n\nNote: the 401 error body uses `code`, `message`, `param`, and `type` (there is no `status` field), and `type` is `invalid_request_error`.","content":{"application/json":{"schema":{"type":"object","properties":{"error":{"type":"object","properties":{"message":{"type":"string"},"type":{"type":"string"},"param":{"type":"string","nullable":true},"code":{"type":"string"}}}}}}}},"RateLimitError":{"description":"Rate Limited - You have exceeded your request limits (TPM/RPM). Slow down or increase your limits.","content":{"application/json":{"schema":{"type":"object","properties":{"error":{"type":"object","properties":{"message":{"type":"string"},"type":{"type":"string"},"code":{"type":"string"},"status":{"type":"integer"}}}}}}}}}},"paths":{"/api/v1/responses":{"post":{"operationId":"createResponse","tags":["Responses"],"summary":"Create Response","description":"Creates responses with conversation state management. Supports previous_response_id for context continuity, function calling, web search, and file inputs. Compatible with OpenAI, Azure, and X-AI (Grok) providers.","requestBody":{"required":true,"content":{"application/json":{"schema":{"type":"object","required":["model","input"],"properties":{"model":{"type":"string","description":"Model ID in provider/model format. Examples: openai/o3, openai/gpt-4.1, x-ai/grok-4"},"input":{"oneOf":[{"type":"string","description":"Simple text input"},{"type":"array","description":"Array of message objects with role and content","items":{"type":"object","properties":{"role":{"type":"string","enum":["user","assistant","system"],"description":"Role of the message"},"content":{"oneOf":[{"type":"string"},{"type":"array"}],"description":"Content as string or array of content blocks (text, files, etc.)"}}}}],"description":"User input - can be a simple string or array of message objects for multimodal/file inputs"},"previous_response_id":{"type":"string","description":"ID of a previous response to continue the conversation. Maintains context across requests."},"stream":{"type":"boolean","default":false,"description":"Enable streaming responses for real-time output"},"tools":{"type":"array","description":"Array of tool definitions. Supports custom functions and web_search tool.","items":{"type":"object","properties":{"type":{"type":"string","enum":["function","web_search"],"description":"Type of tool - 'function' for custom functions, 'web_search' for web search capability"},"name":{"type":"string","description":"Function name (for function tools)"},"description":{"type":"string","description":"Function description (for function tools)"},"parameters":{"type":"object","description":"Function parameters schema (for function tools)"},"filters":{"type":"object","description":"Filters for web search (for web_search tools)","properties":{"allowed_domains":{"type":"array","items":{"type":"string"},"description":"List of allowed domains for web search"}}}}}},"tool_choice":{"type":"string","enum":["auto","none"],"default":"auto","description":"Controls tool usage. 'auto' lets model decide, 'none' disables tools."},"temperature":{"type":"number","minimum":0,"maximum":2,"default":1,"description":"Sampling temperature for randomness control"},"max_tokens":{"type":"integer","description":"Maximum tokens to generate"},"background":{"type":"boolean","default":false,"description":"Run response generation in background"}}}}}},"responses":{"200":{"description":"Successful response","content":{"application/json":{"schema":{"type":"object","properties":{"id":{"type":"string","description":"Unique response ID (use for previous_response_id)"},"object":{"type":"string"},"created_at":{"type":"integer","description":"Unix timestamp"},"model":{"type":"string","description":"Model used"},"output":{"type":"array","description":"Array of output objects (reasoning, messages, etc.)","items":{"type":"object","properties":{"id":{"type":"string"},"type":{"type":"string","enum":["reasoning","message","function_call"]},"role":{"type":"string"},"status":{"type":"string"},"content":{"type":"array"}}}},"background":{"type":"boolean","description":"Whether request ran in background"},"error":{"type":"string","nullable":true,"description":"Error message if any"}}}}}},"400":{"description":"Bad Request - Invalid parameters"},"401":{"$ref":"#/components/responses/UnauthorizedError"},"429":{"$ref":"#/components/responses/RateLimitError"},"500":{"description":"Internal Server Error"}}}}}}
```


---

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