Messages (Anthropic)

POST /v1/messages — drop-in Anthropic-compatible endpoint, used by Claude Code and any Anthropic SDK.

Last updated May 1, 2026

The Messages endpoint speaks the Anthropic Messages wire format. Any client targeting https://api.anthropic.com/v1/messages can be redirected to Cocobox.

POST https://api.cocobox.io/v1/messages

Request

Field	Type	Description
`model` required	string	Model alias or full id. See Models.
`messages` required	Message[]	Alternating `user` / `assistant` turns. Each `content` may be a string or an array of content blocks.
`system` optional	string	System prompt — equivalent to OpenAI's system role message.
`max_tokens` required	integer	Maximum output tokens. Required by the Anthropic format.
`stream` optional	boolean	If true, stream as SSE. Default: `false`
`temperature` optional	number	Sampling temperature, 0–1. Default: `1`
`top_p` optional	number	Nucleus sampling.
`stop_sequences` optional	string[]	Up to 4 stop sequences.
`tools` optional	Tool[]	Anthropic-format tool definitions (`{ name, description, input_schema }`). Passthrough — orchestrate yourself or use MCP.
`tool_choice` optional	object	`{ "type": "auto" \| "any" \| "tool", "name": "..." }`.
`metadata` optional	object	`{ "user_id": "..." }`. Forwarded to the provider for abuse monitoring.

Response (non-streaming)

{
  "id": "msg_01HF2X…",
  "type": "message",
  "role": "assistant",
  "model": "sonnet",
  "stop_reason": "end_turn",
  "stop_sequence": null,
  "usage": { "input_tokens": 24, "output_tokens": 18 },
  "content": [
    { "type": "text", "text": "SELECT id, total FROM orders ORDER BY created_at DESC LIMIT 10;" }
  ]
}

Count tokens

A companion endpoint counts tokens for a request without spending credits.

POST https://api.cocobox.io/v1/messages/count_tokens

{
  "model": "sonnet",
  "messages": [{ "role": "user", "content": "SELECT * FROM users;" }]
}

{ "input_tokens": 9 }

Streaming

Set "stream": true. Cocobox emits the standard Anthropic event sequence:

event: message_start
data: {"type":"message_start","message":{"id":"msg_…","model":"sonnet", … }}

event: content_block_start
data: {"type":"content_block_start","index":0,"content_block":{"type":"text","text":""}}

event: content_block_delta
data: {"type":"content_block_delta","index":0,"delta":{"type":"text_delta","text":"SELECT"}}

…

event: content_block_stop
data: {"type":"content_block_stop","index":0}

event: message_delta
data: {"type":"message_delta","delta":{"stop_reason":"end_turn","stop_sequence":null},"usage":{"output_tokens":18}}

event: message_stop
data: {"type":"message_stop"}

Examples

curl https://api.cocobox.io/v1/messages \
-H "x-api-key: $COCOBOX_API_KEY" \
-H "anthropic-version: 2023-06-01" \
-H "Content-Type: application/json" \
-d '{
  "model": "sonnet",
  "max_tokens": 1024,
  "messages": [
    { "role": "user", "content": "Write a CTE that ranks customers by lifetime spend." }
  ]
}'

import Anthropic from '@anthropic-ai/sdk';

const client = new Anthropic({
apiKey: process.env.COCOBOX_API_KEY,
baseURL: 'https://api.cocobox.io',
});

const msg = await client.messages.create({
model: 'sonnet',
max_tokens: 1024,
messages: [{ role: 'user', content: 'SHOW DATABASES;' }],
});
console.log(msg.content[0].type === 'text' ? msg.content[0].text : '');

from anthropic import Anthropic

client = Anthropic(
  api_key=os.environ["COCOBOX_API_KEY"],
  base_url="https://api.cocobox.io",
)

msg = client.messages.create(
  model="opus",
  max_tokens=2048,
  messages=[{"role": "user", "content": "Audit this schema for missing indexes: …"}],
)
print(msg.content[0].text)

# Claude Code expects an Anthropic-compatible endpoint.
export ANTHROPIC_BASE_URL=https://api.cocobox.io
export ANTHROPIC_API_KEY=sk-coco-…
claude --model sonnet

Tools

Tools follow the Anthropic format. Like the OpenAI surface, tools are passthrough on /v1/messages — you receive tool_use blocks in the response and orchestrate the call yourself. For automatic tool execution against your databases, use MCP — or use a client (Claude Code, Cursor, Zed, opencode) that already integrates the Cocobox MCP server.

{
  "model": "sonnet",
  "max_tokens": 1024,
  "messages": [{ "role": "user", "content": "How many active users last week?" }],
  "tools": [
    {
      "name": "sql_run",
      "description": "Run a read-only SQL query.",
      "input_schema": {
        "type": "object",
        "properties": { "sql": { "type": "string" } },
        "required": ["sql"]
      }
    }
  ]
}

Status codes

Identical to Chat completions. See Errors for the response envelope.