Provider for Anthropic's Claude Messages API.

Uses Req for HTTP calls. Since Anthropic's wire format uses content blocks (the most expressive format), this provider has the simplest normalization.

Config

Required:

• :api_key - Anthropic API key
• :model - Model name (e.g., "claude-opus-4-6", "claude-sonnet-4-6", "claude-haiku-4-5")

Optional:

• :max_tokens - Max output tokens (default: 4096)
• :system_prompt - System prompt string
• :api_url - Base URL (default: "https://api.anthropic.com")
• :api_version - API version header (default: "2023-06-01")
• :extra_headers - Additional headers as [{name, value}]
• :req_options - Additional options passed to Req (useful for testing)
• :extended_thinking - Enable extended thinking. Pass a keyword list with :budget_tokens (e.g., [budget_tokens: 5000]). Thinking blocks are returned in the message content and must be round-tripped verbatim in subsequent turns (Anthropic requires the signature field).
• :on_event - Streaming event callback (event -> :ok). Called for each streaming delta. When used via Server.stream_chat/4, event is a normalized envelope map:
  • %{v: 1, seq:, correlation_id:, turn:, ts_ms:, event: :text_delta, payload: text}
  • %{v: 1, seq:, correlation_id:, turn:, ts_ms:, event: :thinking_delta, payload: text} Pass via Server.stream_chat/4 opts: on_event: fn event -> ... end. Note: direct callers of Alloy.Provider.Anthropic.stream/4 (without Turn) receive provider-native tuples (for example {:thinking_delta, text}).

Example

Alloy.run("What is Elixir?",
  provider: {Alloy.Provider.Anthropic,
    api_key: System.get_env("ANTHROPIC_API_KEY"),
    model: "claude-sonnet-4-6"
  }
)