# `Alloy.Provider.Anthropic`
[🔗](https://github.com/alloy-ex/alloy/blob/v0.10.1/lib/alloy/provider/anthropic.ex#L1)

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"
      }
    )

# `stream`

Stream a completion using Anthropic's SSE streaming API.

Calls `on_chunk` for each text delta as it arrives. Accumulates all
content blocks and returns the same `{:ok, completion_response()}` shape
as `complete/3` once the stream finishes.

---

*Consult [api-reference.md](api-reference.md) for complete listing*