Skip to main content
The anthropic provider supports the Anthropic /v1/messages endpoint for Claude models.

​
Quick Start

client<llm> MyClient {
  provider "anthropic"
  options {
    model "claude-sonnet-4-20250514"
    temperature 0
  }
}

​
Authentication

Set your Anthropic API key as an environment variable: 
export ANTHROPIC_API_KEY="your-api-key-here"
Or specify it explicitly in your BAML configuration: 
client<llm> MyClient {
  provider "anthropic"
  options {
    api_key env.MY_ANTHROPIC_KEY
    model "claude-sonnet-4-20250514"
  }
}

​
Configuration Options

​
BAML-Specific Options

These options modify the API request sent to Anthropic.
​
api_key
string
default:"env.ANTHROPIC_API_KEY"
Passed as a bearer token in the Authorization header: Authorization: Bearer $api_key
​
base_url
string
default:"https://api.anthropic.com"
The base URL for the Anthropic API.
​
headers
object
Additional headers to send with requests.Unless specified, BAML injects this default header:
"anthropic-version": "2023-06-01"
Example:
client<llm> MyClient {
  provider "anthropic"
  options {
    api_key env.MY_ANTHROPIC_KEY
    model "claude-sonnet-4-20250514"
    headers {
      "X-My-Header" "my-value"
    }
  }
}

​
Supported Models

​
model
string
required
The Claude model to use.
ModelUse CaseReleaseContextFeatures
claude-opus-4-1-20250805Complex coding, AI agentsAug 2025200KMost powerful reasoning
claude-sonnet-4-20250514Default choice, versatileMay 2025200K-1MHybrid reasoning modes
claude-3-5-haiku-20241022Fast, cost-efficientOct 2024200KSpeed optimized
You can specify any model name - BAML won’t validate whether it exists.See the Anthropic documentation for the latest models.

​
Model Parameters

These parameters are passed directly to the Anthropic API.
​
max_tokens
int
default:"4069"
The maximum number of tokens to generate.
Common parameters:
  • temperature - Controls randomness (0-1)
  • max_tokens - Maximum tokens to generate (required by Anthropic)
  • top_p - Nucleus sampling parameter
  • top_k - Top-k sampling parameter
  • stop_sequences - Array of sequences that stop generation
For all options, see the Anthropic API documentation.

​
Media Handling

Anthropic’s default behavior converts PDFs to base64 (send_base64) while keeping other media types as URLs (send_url). This is because Anthropic’s API requires PDFs to be base64-encoded.

​
Features

  • Streaming: Supported for real-time response generation
  • Multimodal: Supports text, image, and PDF inputs
  • Extended Thinking: Available with Opus-4 and Sonnet-4 models
  • Tool Use: Native support for function calling

​
System Messages

BAML automatically constructs the system field from your prompt if necessary. Only the first system message is used; subsequent ones are cast to the assistant role.

​
Do Not Set

​
system
DO NOT USE
BAML automatically constructs this from your prompt.
​
messages
DO NOT USE
BAML automatically constructs this from your prompt.
​
stream
DO NOT USE
BAML automatically sets this based on how you call the client in your code.

Build docs developers (and LLMs) love

Get started for freeTalk to us