Openrouter API

OpenRouter API

OpenRouter is a unified API in front of 300+ LLMs. Schema is OpenAI-compatible at /api/v1/chat/completions plus OpenRouter-only extensions (models[], provider, plugins, reasoning, cache_control, presets, :suffix shortcuts). Auth is Authorization: Bearer <OPENROUTER_API_KEY>.

Base URL & auth

POST https://openrouter.ai/api/v1/chat/completions
Authorization: Bearer $OPENROUTER_API_KEY
Content-Type: application/json

Optional attribution headers (enable leaderboard ranking):

• HTTP-Referer: <YOUR_SITE_URL>
• X-OpenRouter-Title: <YOUR_SITE_NAME> (X-Title also accepted)
• X-OpenRouter-Categories: <comma,separated>

API keys are created at https://openrouter.ai/keys. Each key supports a credit limit and works for OAuth flows. OpenRouter is a GitHub secret-scanning partner — leaked sk-or-... keys trigger email notification.

Three integration paths

Use OpenRouter SDKs by default. Reference the OpenAI SDK only when user explicitly asks.

Quickstart (TS SDK)

import OpenRouter from '@openrouter/sdk';

const client = new OpenRouter({ apiKey: process.env.OPENROUTER_API_KEY });

const completion = await client.chat.send({
  model: 'openai/gpt-5.2',
  messages: [{ role: 'user', content: 'What is the meaning of life?' }],
});
console.log(completion.choices[0].message.content);

Quickstart (Python SDK)

from openrouter import OpenRouter
import os

with OpenRouter(api_key=os.getenv("OPENROUTER_API_KEY")) as client:
    response = client.chat.send(
        model="openai/gpt-5.2",
        messages=[{"role": "user", "content": "What is the meaning of life?"}],
    )
    print(response.choices[0].message.content)

Quickstart (raw HTTP)

curl https://openrouter.ai/api/v1/chat/completions \
  -H "Authorization: Bearer $OPENROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model":"openai/gpt-5.2","messages":[{"role":"user","content":"hi"}]}'

Model identifiers

Format: <provider>/<model> (e.g., anthropic/claude-sonnet-4.6, openai/gpt-5.2, google/gemini-3-flash-preview, meta-llama/llama-3.3-70b-instruct, deepseek/deepseek-v3.2). Browse all: https://openrouter.ai/models. List via API: GET /api/v1/models?supported_parameters=tools&output_modalities=text.

Suffix shortcuts

Combinable: openai/gpt-oss-20b:free:online.

Special model slugs

• openrouter/auto — Auto Router (NotDiamond-powered prompt-aware model selection)
• openrouter/bodybuilder — natural-language → structured request bodies for parallel multi-model fan-out (free)
• @preset/<slug> — invoke a saved preset (system prompt + params + provider rules) by name. Configure at https://openrouter.ai/settings/presets. Also usable as preset: "<slug>" field or model: "openai/gpt-4@preset/<slug>" (combined). Per-request params shallow-merge over preset config.

Request body — top-level shape

type Request = {
  // Either messages or prompt
  messages?: Message[];
  prompt?: string;

  model?: string;           // omit = user default
  models?: string[];        // model fallbacks in order

  stream?: boolean;
  stop?: string | string[];
  response_format?: ResponseFormat;       // json_object | json_schema
  tools?: Tool[];
  tool_choice?: ToolChoice;
  parallel_tool_calls?: boolean;          // default true

  // OpenRouter-only
  provider?: ProviderPreferences;         // see references/routing.md
  plugins?: Plugin[];                     // web, file-parser, response-healing, context-compression, auto-router
  reasoning?: ReasoningConfig;            // see references/reasoning.md
  preset?: string;
  user?: string;                          // stable end-user ID for abuse detection
  debug?: { echo_upstream_body?: boolean }; // streaming only

  // Standard sampling — see references/api-reference.md
  max_tokens?: number;
  temperature?: number;
  top_p?: number; top_k?: number; min_p?: number; top_a?: number;
  frequency_penalty?: number; presence_penalty?: number; repetition_penalty?: number;
  seed?: number; logit_bias?: Record<number, number>;
  logprobs?: boolean; top_logprobs?: number;
  prediction?: { type: 'content'; content: string };
  verbosity?: 'low' | 'medium' | 'high' | 'xhigh' | 'max';
};

Unsupported parameters for the chosen model are silently ignored; the rest forward to the upstream. To require providers that support all parameters, set provider.require_parameters: true.

Response shape

{
  "id": "gen-xxxxxxxxxxxxxx",
  "model": "openai/gpt-4o",
  "object": "chat.completion",
  "choices": [{
    "finish_reason": "stop",
    "native_finish_reason": "stop",
    "message": { "role": "assistant", "content": "Hello there!" }
  }],
  "usage": {
    "prompt_tokens": 10,
    "completion_tokens": 4,
    "total_tokens": 14,
    "prompt_tokens_details": { "cached_tokens": 0, "cache_write_tokens": 0 },
    "completion_tokens_details": { "reasoning_tokens": 0 },
    "cost": 0.00014
  }
}

Streaming chunks have delta instead of message and object: "chat.completion.chunk". The final chunk before data: [DONE] carries usage with empty choices.

finish_reason is normalized to one of: tool_calls, stop, length, content_filter, error. Raw provider value is in native_finish_reason. The generation ID is also returned in the X-Generation-Id response header.

Errors

{ "error": { "code": 400, "message": "...", "metadata": { ... } } }

Mid-stream errors (HTTP 200 already sent) arrive as a final SSE chunk with top-level error and a choice with finish_reason: "error". See streaming.md.

Feature map

Always-fresh docs

OpenRouter exposes Markdown of any docs page by appending .md to the URL, plus aggregated llms-full.txt files per section. When reference material here is insufficient for a specific edge case, fetch the latest from:

• Quickstart: https://openrouter.ai/docs/quickstart/llms-full.txt
• API reference: https://openrouter.ai/docs/api/reference/llms-full.txt
• Features: https://openrouter.ai/docs/guides/features/llms-full.txt
• Routing: https://openrouter.ai/docs/guides/routing/llms-full.txt
• Plugins: https://openrouter.ai/docs/guides/features/plugins/llms-full.txt
• Multimodal: https://openrouter.ai/docs/guides/overview/multimodal/llms-full.txt
• Best practices (caching, reasoning): https://openrouter.ai/docs/guides/best-practices/llms-full.txt
• Auth (BYOK, OAuth): https://openrouter.ai/docs/guides/overview/auth/llms-full.txt
• Administration (usage accounting): https://openrouter.ai/docs/guides/administration/llms-full.txt
• Server tools (web search): https://openrouter.ai/docs/guides/features/server-tools/llms-full.txt
• OpenAPI spec: https://openrouter.ai/openapi.yaml or .json

Append .md to any docs URL for clean Markdown of that single page.

Common pitfalls

• prompt and messages are mutually exclusive — pick one.
• The tools array must be repeated on every turn of an agentic loop. The router validates the schema each call. Forgetting to append the assistant's tool-call message to history before the tool-result message breaks Anthropic models.
• Anthropic automatic caching (top-level cache_control) only routes to the Anthropic provider — Bedrock and Vertex AI are excluded. Per-block cache_control works on all three.
• max_tokens cap is context_length - prompt_length, not unbounded.
• OpenAI o-series and some reasoning models do not return reasoning tokens even when present internally. reasoning.exclude: true controls visibility, not internal use.
• debug.echo_upstream_body only works with stream: true and is dev-only — it can leak request internals.
• :online shortcut is the deprecated web plugin routed through openrouter/auto. New code uses the openrouter:web_search server tool so the model decides when to search.
• Mid-stream errors keep HTTP 200 because headers were already sent. Detect via the top-level error field on a chunk plus finish_reason: "error".
• BYOK keys always try first before OpenRouter shared capacity, regardless of provider.order.
• Free-tier (:free) rate limits are global per account — extra API keys do not multiply quota.
• The usage: { include: true } and stream_options: { include_usage: true } parameters are deprecated — usage is always included now.