---
title: "Create a message"
method: POST
path: "/messages"
tags: ["Messages"]
---

# Create a message

`POST /messages`

## Request body

- AnthropicMessageRequest
  - `model` string, required
  - `messages` object[], required
    - `role` 'user' | 'assistant', required
    - `content` union, required
      - string
      - object[]
  - `system` union
    - string
    - object[]
  - `max_tokens` integer, required
  - `stop_sequences` string[]
  - `stream` boolean
  - `temperature` number
  - `top_p` number
  - `top_k` integer
  - `tools` object[]
  - `tool_choice` object
  - `thinking` object — Anthropic extended thinking. Set on Claude 4 / Claude Opus models that support thinking. The model emits a hidden reasoning pass before its final answer.
    - `type` 'enabled' | 'disabled' | 'adaptive'
    - `budget_tokens` integer — Cap on the hidden thinking pass.
  - `mcp_servers` unknown
  - `metadata` object

## Response `200`

OK

- AnthropicMessageResponse
  - `id` string
  - `type` 'message'
  - `role` 'assistant'
  - `content` object[]
    - `type` 'text' | 'tool_use' | 'thinking'
    - `text` string
  - `model` string
  - `stop_reason` 'end_turn' | 'max_tokens' | 'stop_sequence' | 'tool_use'
  - `stop_sequence` string, nullable
  - `usage` object
    - `input_tokens` integer
    - `output_tokens` integer
    - `cache_creation_input_tokens` integer — Tokens written to Anthropic prompt-cache during this request. Charged separately by Anthropic; see Operations / Billing & Usage.
    - `cache_read_input_tokens` integer — Tokens served out of Anthropic prompt-cache (cheaper than fresh input).
    - `server_tool_use` object — Set when Anthropic's server-side tools (e.g. `web_search_20260209`) ran during this turn. Tracked for built-in tool billing.

---

[API](https://skmtc.dev/orcarouter/apis/orcarouter-api.md) · [All operations](https://skmtc.dev/orcarouter/apis/orcarouter-api/llms.txt) · [OpenAPI document](https://skmtc-service-production.skmtc.workers.dev/v1/apis/orcarouter/orcarouter-api/revisions/9c5cc5d00311/schema)