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OpenRouter Multi-Model Chat Completion Gateway
OpenRouter Multi-Model Chat Completion Gateway is a paid API for AI agents from openrouter.withzero.xyz, paid per call via MPP, $0.005444/call, status unknown (last checked 2026-09-15).
Routes OpenAI-compatible chat completion requests to any of 700+ OpenRouter models, billed at cost per token with no markup
Price / call$0.005444
Success—
StatusUnknown
How this service works
OpenAI-compatible chat completion via any OpenRouter model, paid in one shot: price = estimated input tokens x input rate + max_tokens x output rate, resolved before the call and capped per model (from $0.10 for cheap models up to $5 for premium models like anthropic/claude-fable-5). For longer generations use POST /api/v1/chat/completions/metered. 📖 Full guide: https://openrouter.withzero.xyz/llms.txt
Output
Returns an OpenAI-compatible chat completion object containing: the generated message text, role, optional tool_call arrays, finish_reason, token usage counts (prompt, completion, total), and a billing object showing promptTokens, completionTokens, and settledUsdcMicro (the actual USDC cost charged for the request).
Example use cases
Compare responses across multiple models
“Send this prompt to both google/gemini-flash-1.5 and meta-llama/llama-3.1-8b-instruct through the OpenRouter gateway: system message 'You are a concise technical writer', user message 'Explain what a REST API is in two sentences.' Use max_tokens of 200 for each and show me both responses so I can compare the output quality.”
Tool calling with a premium model
“Using the OpenRouter gateway, send a chat completion request to anthropic/claude-opus-4 with tool calling enabled. System message: 'You are a helpful assistant with access to a weather tool.' User message: 'What is the weather like in Paris right now?' Define a get_weather tool with a location parameter, set max_tokens to 512, and return whatever tool_call the model produces.”
Budget-capped creative writing generation
“Via the OpenRouter gateway, send a creative writing request to mistralai/mistral-small with a max_tokens budget of 1024 so I stay within a low cost cap. System message: 'You are a creative fiction author', user message: 'Write the opening paragraph of a mystery novel set in 1920s New Orleans.' Use temperature 0.9 for more creative output.”
Technical details
Endpoint
POSThttps://openrouter.withzero.xyz/api/v1/chat/completionsWhen to prefer
Choose this endpoint when you need to access multiple LLM providers (OpenAI, Anthropic, Google, Meta, Mistral, etc.) through a single OpenAI-compatible interface without managing separate API keys or subscriptions. Especially useful when you want transparent, at-cost token billing via crypto micropayments, need fallback model routing, or want to switch between model providers without changing your integration code.
Side effects
- Model ID not found on OpenRouter — returns error if model string is invalid or unavailable
- Insufficient USDC balance to cover estimated cost — call rejected before execution
- max_tokens set too low — completion truncated at finish_reason='length'
- messages array empty or malformed — schema validation error
- stream:true submitted — rejected because only stream:false is supported
- Network timeout to upstream OpenRouter — propagated as gateway error
- Rate limiting from upstream provider for selected model
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| seed | integer | Random seed for deterministic outputs (support varies by model). |
| stop | — | Stop sequence(s): generation halts when any is produced. |
| modelrequired | string | OpenRouter model ID, e.g. "openai/gpt-4o-mini", "anthropic/claude-haiku-4-5", "google/gemini-flash-1.5". Use GET /api/v1/models to list all available models with pricing. |
| route | string | OpenRouter routing strategy, e.g. "fallback". Requires an explicit `models` list so every candidate model can be priced. |
| tools | array | OpenAI-format tool definitions for function calling. |
| top_k | integer | Top-k sampling: limit to the k most likely next tokens. |
| top_p | number | Nucleus sampling probability mass 0–1. Alternative to temperature. |
| models | array | Fallback model list for OpenRouter auto-routing. Tried in order if the primary model is unavailable. The price reservation is taken at the most expensive rates across model + models, since any of them may serve the call; the difference is refunded on the metered route. |
| streamrequired | boolean | Must be false — streaming is not supported in v1. |
| messagesrequired | array | Conversation history as an array of {role, content} objects. At minimum one user message is required. |
| reasoning | object | OpenRouter reasoning config for thinking models. Reasoning tokens bill as output tokens and are added to the price reservation. |
| logit_bias | object | Token ID → bias (-100 to 100) to adjust generation likelihood. |
| max_tokensrequired | integer | Maximum output tokens. Controls your spend ceiling — the price reservation is input estimate x input_rate + (max_tokens + reasoning budget) x output_rate. The fixed route rejects requests reserving above its cap; use the metered route for large values. |
| transforms | array | OpenRouter prompt transforms, e.g. ["middle-out"] for context compression. |
| temperature | number | Sampling temperature 0–2. Higher = more random. Defaults to model default (usually ~1.0). |
| tool_choice | — | Tool selection strategy: "auto", "none", "required", or a specific tool name. |
| response_format | object | Output format, e.g. {"type":"json_object"} to force JSON output. |
| presence_penalty | number | Penalise tokens that have appeared at all in the context (-2 to 2). |
| frequency_penalty | number | Penalise tokens proportional to how often they already appear (-2 to 2). |
| repetition_penalty | number | Repetition penalty multiplier (1.0 = no penalty). Some models only. |
Output
Schema · Response
| Field | Type | Description |
|---|---|---|
| idrequired | string | |
| modelrequired | string | |
| usage | object | |
| objectrequired | string | |
| billingrequired | object | |
| choicesrequired | array | |
| createdrequired | number | |
| system_fingerprint | string |
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