> This page is for NeMo Relay, version dev.
> For other versions, use one of these documentation indexes:
> - Latest (v0.11.1) (default): https://docs.nvidia.com/nemo/relay/latest/llms.txt
> - dev: https://docs.nvidia.com/nemo/relay/dev/llms.txt
> - v0.11.1: https://docs.nvidia.com/nemo/relay/v0.11.1/llms.txt
> - v0.10.4: https://docs.nvidia.com/nemo/relay/v0.10.4/llms.txt
> - v0.9.4: https://docs.nvidia.com/nemo/relay/v0.9.4/llms.txt
> - v0.8.4: https://docs.nvidia.com/nemo/relay/v0.8.4/llms.txt
> - v0.7.3: https://docs.nvidia.com/nemo/relay/v0.7.3/llms.txt

> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.nvidia.com/nemo/relay/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.nvidia.com/nemo/relay/_mcp/server.

# Module anthropic

> Built-in codec for the Anthropic Messages API.

Generated from `cargo doc --no-deps -p nemo-relay-builtins -p nemo-relay-diagnostics -p nemo-relay-logging -p nemo-relay-plugin-host -p nemo-relay-codecs -p nemo-relay -p nemo-relay-runtime -p nemo-relay-model-pricing -p nemo-relay-resource-metrics -p nemo-relay-observability -p nemo-relay-adaptive -p nemo-relay-pii-redaction -p nemo-relay-ffi -p nemo-relay-types -p nemo-relay-plugin -p nemo-relay-worker-proto -p nemo-relay-worker`.

Built-in codec for the Anthropic Messages API.

Implements \[`LlmCodec`] (request decode/encode) and \[`LlmResponseCodec`] (response decode) for the Anthropic Messages API format.

## Anthropic-specific patterns handled

* **Content blocks**: Heterogeneous array of `text`, `tool_use`, `thinking`, `redacted_thinking`, `mcp_tool_use`, `server_tool_use` blocks
* **Top-level system**: System prompt is a top-level field, not inside messages
* **stop_reason**: Maps to \[`FinishReason`] (not `finish_reason`)
* **Tool definitions**: Uses `input_schema` instead of `parameters`
* **Tool choice**: `{"type":"auto"}` / `{"type":"any"}` / `{"type":"tool","name":"..."}`
* **Cache tokens**: `cache_read_input_tokens` / `cache_creation_input_tokens`

## Structs

* [AnthropicMessagesCodec](/nemo/relay/dev/reference/api/rust-library-reference/nemo-relay-codecs/anthropic/struct-anthropicmessagescodec): Built-in codec for the Anthropic Messages API.
* [AnthropicMessagesStreamingCodec](/nemo/relay/dev/reference/api/rust-library-reference/nemo-relay-codecs/anthropic/struct-anthropicmessagesstreamingcodec): Streaming counterpart to [`AnthropicMessagesCodec`](/nemo/relay/dev/reference/api/rust-library-reference/nemo-relay-codecs/anthropic/struct-anthropicmessagescodec).