Anthropic Format - /v1/messages - Antigravity Manager

Endpoint

POST http://127.0.0.1:8045/v1/messages

The native Anthropic/Claude protocol endpoint provides full support for Claude Code CLI and advanced features like extended thinking, system prompts, and tool use.

Authentication

x-api-key

string

required

Anthropic-style API key header

x-api-key: sk-antigravity

Alternatively, use standard Bearer authentication:

Authorization

string

Bearer token format

Authorization: Bearer sk-antigravity

Request Headers

Content-Type

string

required

Must be application/json

anthropic-version

string

API version, e.g., 2023-06-01

anthropic-beta

string

Beta features to enable. Automatically injected:

anthropic-beta: claude-code-20250219,interleaved-thinking-2025-05-14

Request Body

model

string

required

Model identifier:

claude-sonnet-4-6 - Latest Claude Sonnet 4.6
claude-sonnet-4-6-thinking - With extended thinking
claude-opus-4-6-thinking - Opus with thinking
gemini-3-pro-high - Mapped to Gemini (via protocol conversion)

messages

array

required

Conversation messages in Anthropic format

Show Message Object

role

string

required

Message role: user or assistant

content

string | array

required

Message content. Can be:

String: Plain text
Array: Multi-modal blocks (text, images, tool_use, tool_result)

system

string | array

System prompt to guide model behavior. Can be:

String: Simple system message
Array: Structured system blocks for advanced control

max_tokens

integer

required

Maximum tokens to generate. Required for Claude protocol.

Unlike OpenAI format, max_tokens is mandatory for Anthropic endpoints.

stream

boolean

default:"false"

Enable Server-Sent Events (SSE) streaming

temperature

number

Sampling temperature (0.0 to 1.0)

top_p

number

Nucleus sampling (0.0 to 1.0)

top_k

integer

Top-K sampling parameter

thinking

object

Extended thinking configuration for reasoning models

Show Thinking Config

type

string

required

Thinking mode:

enabled - Enable with budget
adaptive - Dynamic budget (maps to fixed budget internally)
disabled - No extended thinking

budget_tokens

integer

Token budget for reasoning:

Low: 8192
Medium: 16384
High: 24576

effort

string

Effort level: low, medium, high, max

output_config

object

Output configuration (Claude API v2.0.67+)

Show Output Config

effort

string

Model reasoning effort: low, medium, high

tools

array

Available tools for function calling

Show Tool Definition

name

string

required

Tool name

description

string

Tool description

input_schema

object

required

JSON Schema for tool parameters

Server tools like web_search can be enabled via:

Show Server Tool

type

string

Server tool type, e.g., web_search_20250305

name

string

Tool name: web_search

Response Format

Non-Streaming Response

string

Unique message identifier

type

string

Response type, always message

role

string

Always assistant

model

string

Model used for generation

content

array

Response content blocks

Show Content Blocks

type

string

Block type: text, thinking, tool_use, image

text

string

Text content (for text blocks)

thinking

string

Reasoning content (for thinking blocks)

signature

string

Cryptographic signature for thinking/tool_use blocks

string

Tool call ID (for tool_use blocks)

name

string

Tool name (for tool_use blocks)

input

object

Tool parameters (for tool_use blocks)

stop_reason

string

Completion reason: end_turn, max_tokens, tool_use, stop_sequence

usage

object

Token usage statistics

Show Usage Object

input_tokens

integer

Prompt tokens

output_tokens

integer

Completion tokens

cache_read_input_tokens

integer

Cached tokens read (prompt caching)

cache_creation_input_tokens

integer

Tokens cached for future use

Example: Basic Chat

curl -X POST http://127.0.0.1:8045/v1/messages \
  -H "Content-Type: application/json" \
  -H "x-api-key: sk-antigravity" \
  -d '{
    "model": "claude-sonnet-4-6",
    "max_tokens": 1024,
    "messages": [
      {"role": "user", "content": "Explain quantum computing"}
    ]
  }'

Example: With System Prompt

curl -X POST http://127.0.0.1:8045/v1/messages \
  -H "Content-Type: application/json" \
  -H "x-api-key: sk-antigravity" \
  -d '{
    "model": "claude-sonnet-4-6",
    "max_tokens": 2048,
    "system": "You are a helpful coding assistant. Always explain your reasoning.",
    "messages": [
      {"role": "user", "content": "Write a Python function to reverse a string"}
    ]
  }'

Example: Extended Thinking

curl -X POST http://127.0.0.1:8045/v1/messages \
  -H "Content-Type: application/json" \
  -H "x-api-key: sk-antigravity" \
  -d '{
    "model": "claude-sonnet-4-6-thinking",
    "max_tokens": 4096,
    "thinking": {
      "type": "enabled",
      "budget_tokens": 16384
    },
    "messages": [
      {"role": "user", "content": "Solve this complex logic puzzle: ..."}
    ]
  }'

Example: Claude Code CLI Integration

# Set environment variables
export ANTHROPIC_API_KEY="sk-antigravity"
export ANTHROPIC_BASE_URL="http://127.0.0.1:8045"

# Run Claude Code CLI
claude "Help me debug this Python code"

Example: Tool Use

curl -X POST http://127.0.0.1:8045/v1/messages \
  -H "Content-Type: application/json" \
  -H "x-api-key: sk-antigravity" \
  -d '{
    "model": "claude-sonnet-4-6",
    "max_tokens": 2048,
    "tools": [
      {
        "name": "get_weather",
        "description": "Get current weather",
        "input_schema": {
          "type": "object",
          "properties": {
            "location": {"type": "string"}
          },
          "required": ["location"]
        }
      }
    ],
    "messages": [
      {"role": "user", "content": "What's the weather in Tokyo?"}
    ]
  }'

Example: Web Search (Server Tool)

curl -X POST http://127.0.0.1:8045/v1/messages \
  -H "Content-Type: application/json" \
  -H "x-api-key: sk-antigravity" \
  -d '{
    "model": "claude-sonnet-4-6",
    "max_tokens": 2048,
    "tools": [
      {
        "type": "web_search_20250305",
        "name": "web_search"
      }
    ],
    "messages": [
      {"role": "user", "content": "What are the latest AI developments?"}
    ]
  }'

Content Block Types

Text Block

{
  "type": "text",
  "text": "Here is my response..."
}

Thinking Block

{
  "type": "thinking",
  "thinking": "Let me analyze this step by step...",
  "signature": "base64-encoded-signature"
}

Tool Use Block

{
  "type": "tool_use",
  "id": "toolu_123abc",
  "name": "get_weather",
  "input": {
    "location": "Tokyo"
  },
  "signature": "base64-encoded-signature"
}

Tool Result Block (in messages)

{
  "role": "user",
  "content": [
    {
      "type": "tool_result",
      "tool_use_id": "toolu_123abc",
      "content": "Temperature: 22°C, Sunny"
    }
  ]
}

Image Upload

{
  "role": "user",
  "content": [
    {
      "type": "image",
      "source": {
        "type": "base64",
        "media_type": "image/jpeg",
        "data": "base64-encoded-image-data"
      }
    },
    {
      "type": "text",
      "text": "What's in this image?"
    }
  ]
}

Features

Full Claude Protocol: 100% compatible with Claude Code CLI and Anthropic SDKs
Extended Thinking: Support for reasoning tokens with signature validation
Tool Use: Client tools, server tools (web_search), and MCP integration
Streaming: Real-time SSE streaming with thinking blocks
Context Caching: Automatic prompt caching for repeated contexts
Multi-modal: Images, documents, audio support

Error Format

{
  "type": "error",
  "error": {
    "type": "invalid_request_error",
    "message": "max_tokens is required"
  }
}

Common error types:

invalid_request_error - Malformed request
authentication_error - Invalid API key
rate_limit_error - Quota exceeded
server_error - Internal error

Overview

Endpoints

Protocol Conversion

Anthropic Format - /v1/messages

Endpoint

Authentication

Request Headers

Request Body

Response Format

Non-Streaming Response

Example: Basic Chat

Example: With System Prompt

Example: Extended Thinking

Example: Claude Code CLI Integration

Example: Tool Use

Example: Web Search (Server Tool)

Content Block Types

Text Block

Thinking Block

Tool Use Block

Tool Result Block (in messages)

Image Upload

Features

Error Format

Build docs developers (and LLMs) love

Overview

Endpoints

Protocol Conversion

​Endpoint

​Authentication

​Request Headers

​Request Body

​Response Format

​Non-Streaming Response

​Example: Basic Chat

​Example: With System Prompt

​Example: Extended Thinking

​Example: Claude Code CLI Integration

​Example: Tool Use

​Example: Web Search (Server Tool)

​Content Block Types

​Text Block

​Thinking Block

​Tool Use Block

​Tool Result Block (in messages)

​Image Upload

​Features

​Error Format

Build docs developers (and LLMs) love

Endpoint

Authentication

Request Headers

Request Body

Response Format

Non-Streaming Response

Example: Basic Chat

Example: With System Prompt

Example: Extended Thinking

Example: Claude Code CLI Integration

Example: Tool Use

Example: Web Search (Server Tool)

Content Block Types

Text Block

Thinking Block

Tool Use Block

Tool Result Block (in messages)

Image Upload

Features

Error Format