> For the complete documentation index, see [llms.txt](https://weavescope.gitbook.io/beam_weaver/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://weavescope.gitbook.io/beam_weaver/partners/anthropic.md).

# Anthropic

BeamWeaver includes a direct Anthropic Messages API provider under `BeamWeaver.Anthropic`.

## Implemented

* `BeamWeaver.Anthropic.ChatModel` implements `BeamWeaver.Core.ChatModel`.
* `BeamWeaver.Anthropic.Tools` renders custom tools and Anthropic server-side tool declarations.
* Requests go through `BeamWeaver.Transport`, so tests can run against fake or replay transports without live credentials.
* Anthropic namespace constructors load defaults from `config :beam_weaver, :anthropic`; put any OS environment reads in your `config/runtime.exs`. Custom routing uses explicit `:endpoint` and `:count_tokens_endpoint` options.
* BeamWeaver messages become Anthropic `messages` plus top-level `system`.
* Tool result messages become user-role `tool_result` blocks.
* Assistant `tool_calls` become Anthropic `tool_use` content blocks.
* Text, image, file/document, thinking, redacted thinking, citations, server tool calls/results, and unknown provider blocks are preserved where possible.
* Responses become assistant messages with normalized usage metadata, cache token details, response metadata, and extracted tool calls.
* Streaming SSE bodies are parsed into text deltas, lifecycle events, typed stream envelopes, and reconstructed final assistant messages.
* The token counting endpoint is exposed through `ChatModel.count_tokens/3`.
* Checked-in model profiles cover Claude Fable 5, Claude Mythos 5, current Claude Opus 4.8/4.7/4.6/4.5/4.1, Claude Sonnet 4.6/4.5, and Claude Haiku 4.5 models, with a permissive fallback for future `claude-*` models.
* Deprecated or retired Claude IDs return tagged `:deprecated_model` errors with `:replacement`, `:expected`, and retirement metadata instead of falling through to the family fallback.
* Request builders include Anthropic spec fields such as `:cache_control`, `:container`, `:metadata`, `:service_tier`, `:diagnostics`, `:speed`, `:user_profile_id`, `:inference_geo`, `:context_management`, `:mcp_servers`, `:thinking`, and `:output_config`.
* Claude Opus 4.7 and later follow Anthropic's current request restrictions: non-`1.0` `:temperature`, any `:top_k`, `:top_p` below `0.99`, and non-adaptive enabled `:thinking` fail before the transport call.

## Usage

```elixir
model =
  BeamWeaver.Anthropic.chat_model(
    model: "claude-haiku-4-5-20251001",
    api_key: "sk-ant-test"
  )

BeamWeaver.Core.ChatModel.invoke(model, [
  BeamWeaver.Core.Message.user("Write a short haiku about the BEAM.")
])
```

Tools are plain request values:

```elixir
tools = [
  BeamWeaver.Anthropic.Tools.web_search(),
  BeamWeaver.Anthropic.Tools.code_execution(),
  BeamWeaver.Anthropic.Tools.web_fetch(),
  BeamWeaver.Anthropic.Tools.function(my_tool, strict: true)
]

BeamWeaver.Core.ChatModel.invoke(model, messages, tools: tools, tool_choice: :auto)
```

Token counting uses Anthropic's count-tokens endpoint:

```elixir
BeamWeaver.Anthropic.ChatModel.count_tokens(model, [
  BeamWeaver.Core.Message.user("Count this.")
])
```

## Remaining Anthropic Work

* Live-cassette expansion for every upstream Anthropic integration cassette.
* Bedrock/Vertex Anthropic routing. The direct Anthropic provider is implemented first.
* Provider-specific files API helpers beyond message/document block support.
* Managed Agents beta resources from Anthropic's OpenAPI spec, such as sessions, environments, skills, memories, vaults, and user profiles, are not exposed as first-class BeamWeaver modules yet; supported request fields can be passed where the Messages API accepts them.
* Exact Python class identity and serialization compatibility. BeamWeaver keeps native Elixir modules and tagged errors.

## Related Guides

* [Models](/beam_weaver/core-components/models.md)
* [Tools](/beam_weaver/core-components/tools.md#server-side-provider-tools)
* [Messages](/beam_weaver/core-components/messages.md#standard-content-blocks)
* [Structured Output](/beam_weaver/core-components/structured_output.md)
* [Custom Middleware](/beam_weaver/core-components/custom_middleware.md#prompt-caching-with-anthropic)


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