Imported from jwmarb/open-webui-openai-compatible (src/proxy/anthropic/AGENTS.md). Install upstream with npx skills add jwmarb/open-webui-openai-compatible --skill anthropic. Copyright stays with the author.

src/proxy/anthropic/

The Anthropic Messages API frontend: POST /v1/messages (routes.py:76). Translates Anthropic requests into a canonical body, sends them upstream via the OpenAI SDK, and translates responses back. Design rationale: ADR-0001.

Vocabulary: CONTEXT.md.

Route flow

routes.py:76-103, in this order — the order is load-bearing:

1. translate_request(raw_body) → canonical (OpenAI-shaped) body.
2. resolve_thinking_model() + apply_thinking_params() — strips :adaptive and injects the thinking config. Without this the suffix reached upstream as a literal model ID and 404'd. :extended is no longer recognised anywhere.
3. prepare_chat_body() → the seven rewrite passes plus the SDK/extra_body split, in one call.
4. _handle_streaming (:107) or _handle_non_streaming (:189).

Cross-package imports — all public

• routes.py:22 — resolve_thinking_model, apply_thinking_params from ../openai/translator.py.
• routes.py:20 — prepare_chat_body from ../../open_webui/request_policy.py.
• routes.py:18-19 — classify_upstream_error, log_upstream_error from src/errors.py; get_current_token, request_refresh, should_refresh from src/auth.py.

No private symbol crosses a package seam. The former from ..openai.routes import _split_body_for_sdk is gone.

Still duplicated with ../openai/routes.py, keep in sync: _SSE_HEADERS (:29 ↔ :31), _RETRY_BACKOFF_CAP (:104 ↔ :36).

401 handling — now symmetric with the OpenAI route

_refresh_for (:37) returns True when the exception is a 401 and should_refresh(get_current_token(), exc.body) finds positive token-fault evidence; it then calls request_refresh(). _token_expired_error_response (:48) returns 503 in Anthropic error format. Three call sites: streaming create (:130), streaming first-chunk (:137), non-streaming (:203).

A 401 without token evidence (e.g. model_access_denied) still passes through as a 401. The earlier asymmetry — where an Anthropic-only client never triggered a refresh — is fixed.

translator.py

517 lines. Request/response translation and the stream lifecycle.

• translate_request (:182): Anthropic → canonical. Default max_tokens 4096. top_k passthrough. output_config.effort stays nested as output_config: {effort} — a bare top-level effort is rejected by every Bedrock model on the gateway (effort: Extra inputs are not permitted). output_config.format maps to response_format json_schema. system, tools, tool_choice, thinking all mapped.
• _map_finish_reason (:245): stop→end_turn, length→max_tokens, tool_calls→tool_use, content_filter→end_turn, unknown→end_turn.
• translate_response (:257): canonical → Anthropic. Upstream thinking_blocks keep their real signature values, so non-streaming multi-turn thinking works at full fidelity.
• create_anthropic_error (:24): the Anthropic error body.

StreamingState (:313) — owns the whole stream lifecycle

The class is the single authority on event ordering. The route feeds chunks and calls finalize() once; it does not infer lifecycle (the old saw_finish flag is gone).

Invariants, each pinned by a test:

Parallel tool calls are buffered, not streamed through. Upstream interleaves tool-call fragments by index; Anthropic requires sequential, non-overlapping blocks (its SDK appends on content_block_start and indexes content[event.index] on delta, so an interleaved stream raises). _buffer_tool_calls (:480) accumulates id/name/arguments per upstream index; _flush_tool_blocks (:379) emits each as a complete start→delta→stop block at finalize(). This trades a little latency on tool calls for wire correctness.

All events are plain dicts; routes.py serializes them via _sse_event (:71).

models.py

47 lines, four shapes, all used at runtime: AnthropicUsage, AnthropicResponse, AnthropicErrorDetail, AnthropicErrorResponse (imported by translator.py:9-14).

The 6 SSE event classes, AnthropicRequest, and every request-side content-block model are deleted. They were declared but unreachable, which implied validation that never happened. translate_request and StreamingState work on raw dicts by design — see the "Deliberately absent" section of CONTEXT.md.

Where to look

Constraints / gotchas

• # type: ignore[union-attr] in the streaming path: do not remove. The SDK stream type is a union pyright cannot narrow.
• Translation order is load-bearing: translate_request → thinking resolution → prepare_chat_body. Do not reorder.
• Never emit a content block while another is open, and never emit an index out of order — Anthropic clients accumulate per open block.
• Every new Anthropic API feature needs a matching translation mapping here. That is the accepted ongoing cost of the translation approach (ADR-0001).
• Package tests: tests/test_anthropic_translator.py (54 tests), tests/test_anthropic_routes.py (25 tests). Both run in CI.