Claude API

What it covers

The direct Claude API centers on POST /v1/messages, with companion endpoints for batches, token counting, models, files, and platform administration. Anthropic also documents access through cloud platforms, whose IAM, billing, and feature availability can differ.

Request shape

curl https://api.anthropic.com/v1/messages \
  -H "Authorization: Bearer $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{"model":"YOUR_MODEL","max_tokens":512,"messages":[{"role":"user","content":"Explain this API response."}]}'

SDKs populate the standard headers, but a raw HTTP integration must send the API version explicitly.

Key endpoints

Endpoint	Description
POST /v1/messages	Create a message (core inference)
POST /v1/messages/batches	Create a batch request
GET /v1/messages/batches/{id}	Retrieve batch status/results
POST /v1/messages/count_tokens	Count tokens before sending
GET /v1/models	List available models
GET /v1/models/{model_id}	Get model details
POST /v1/files	Upload files for use with API
GET /v1/files	List uploaded files

Decision notes

Choose between direct Anthropic access and a cloud marketplace based on required features, identity controls, regional availability, and existing cloud commitments—not model name alone.

Python example: messages API

import httpx

API_KEY = "your_anthropic_api_key"
BASE = "https://api.anthropic.com/v1"

def message(prompt: str, model: str = "claude-sonnet-4-5", max_tokens: int = 1024) -> str:
    """Send a message. The anthropic-version header is required."""
    resp = httpx.post(
        f"{BASE}/messages",
        headers={
            "x-api-key": API_KEY,
            "anthropic-version": "2023-06-01",
            "content-type": "application/json",
        },
        json={
            "model": model,
            "max_tokens": max_tokens,
            "messages": [{"role": "user", "content": prompt}],
        },
        timeout=60,
    )
    if resp.status_code == 429:
        raise RuntimeError("Rate limited — back off and retry")
    resp.raise_for_status()
    data = resp.json()
    return "".join(b.get("text", "") for b in data["content"] if b["type"] == "text")

print(message("Explain dividends in one sentence."))

Notes:

• Auth uses x-api-key header (not Bearer); anthropic-version: 2023-06-01 is mandatory
• Response content is a list of blocks — concatenate text blocks
• Check stop_reason (end_turn, max_tokens, tool_use) to handle truncation
• Use the official anthropic SDK for streaming and tool use in production