* Studio: wire Anthropic server-side context compaction
Anthropic ships server-side context compaction as a beta
(`compact-2026-01-12`). When the rendered prompt crosses the
configured input-token threshold, Anthropic runs an extra LLM pass
that summarises older turns and the request continues against the
compacted prefix. The response carries the original top-level fields
plus a new `context_management` block (with `applied_edits`) and
`usage.iterations[]` accounting per pass.
Per the docs the feature is currently supported on Opus 4.6, Opus 4.7,
Sonnet 4.6, and Mythos preview. The minimum threshold is 50k tokens;
under-50k requests 400.
Changes:
- Add prefix gate + helper `_anthropic_supports_compaction` plus
constants `_ANTHROPIC_COMPACTION_PREFIXES`, `_ANTHROPIC_COMPACTION_BETA`,
`_ANTHROPIC_COMPACTION_TYPE`, `_ANTHROPIC_COMPACTION_MIN`.
- Add `compaction_threshold: Optional[int]` to ChatCompletionRequest
(50k ge bound, 2M le bound). Thread through `routes/inference.py`
-> `stream_chat_completion` -> `_stream_anthropic`.
- In `_stream_anthropic`, when threshold is set AND the model
accepts compaction, attach `context_management.edits[{type:
"compact_20260112", trigger:{type:"input_tokens", value:N}}]` to
the outbound body. Sub-50k values are clamped up to 50k to keep
the request well-formed.
- Refactor the anthropic-beta header builder to merge any combination
of `code-execution-2025-08-25` + `compact-2026-01-12` flags into
one header value. Unrelated betas added at the registry level still
pass through.
- Add `test_anthropic_compaction.py` with 16 cases: gate matrix
(every doc-listed model), correct body shape, threshold clamping,
beta header merge with code execution, silent no-op on unsupported
models, omitted-threshold pass-through.
Live verified end-to-end against the real Anthropic API:
`compact_20260112` accepted on Opus 4.7, response carries
`context_management.applied_edits` + `usage.iterations[]` as
documented. (The first WebFetch-summarised version of these docs
suggested `compact_20260120`; the actual API only accepts
`compact_20260112`, matching the beta-header date. Worth pinning
behind a test so a future doc update can't drift back.)
* [pre-commit.ci] auto fixes from pre-commit.com hooks
for more information, see https://pre-commit.ci
* Address review: drop ge=50_000 clamp + parse usage.iterations[]
Two reviewer follow-ups on the compaction PR:
1. Pydantic ge=50_000 on compaction_threshold was dead code.
FastAPI rejected sub-50k threshold values with a 422 before the
`max(int(...), _ANTHROPIC_COMPACTION_MIN)` clamp in
_stream_anthropic could ever fire. Relaxed the floor to ge=1 so
the in-helper clamp actually does its job; the schema comment
now explains why this is intentional. Added a regression test
that posts a value of 1 and 49_999 through the real request
schema.
2. Anthropic publishes per-iteration token counts in
`usage.iterations[]` whenever a fresh compaction has run, and
the top-level input_tokens / output_tokens cover only the
`message` iteration -- billing must add the compaction
iterations on top. Aggregate compaction iteration tokens into
`last_usage["compaction_input_tokens" / "compaction_output_tokens"]`
so the cost surface (PR 5690) can read them without re-walking
the array, and surface both figures in the closing stream
summary log. Added two tests: one that pins the aggregation on a
compacted turn and one that pins `None` when no fresh
iterations land (so re-applied compaction blocks don't double-bill).
Sourcing: https://platform.claude.com/docs/en/build-with-claude/compaction
* [pre-commit.ci] auto fixes from pre-commit.com hooks
for more information, see https://pre-commit.ci
* Address review: round-trip Anthropic compaction blocks across turns
Codex P1: once context_management is enabled and Anthropic runs
server-side compaction mid-stream, the response carries a
`{type:"compaction", content:"<summary>"}` content block on the
assistant message. The translator only handled text_delta and
input_json_delta on content_block_delta, so the compaction block
was silently dropped. Worse, the request schema's ContentPart
discriminated Union didn't accept `type:"compaction"`, and
_build_external_messages didn't pass it through, so even a
hand-crafted assistant message carrying the block would 422 at
parse time. Net result: Anthropic re-compacted from scratch on
every subsequent turn, wasting input tokens and reasoning budget.
End-to-end backend wiring of the round-trip:
1. SSE translator. _stream_anthropic now tracks a `current_compaction`
state slot. content_block_start with type=="compaction" seeds it
(Anthropic may include the summary on the start event AND/OR
stream it via text_delta events on the same block index --
handle both). text_delta inside a compaction block routes into
the compaction buffer instead of the user-visible content
stream, since the summary is opaque internal state, not
assistant prose. content_block_stop emits a `compaction_block`
tool_event carrying the full summary so the chat-adapter can
persist it. compaction_blocks_seen is surfaced in the closing
summary log.
2. Pydantic schema. Added CompactionContentPart with Tag("compaction")
on the ContentPart Union so requests carrying the block parse
cleanly. Required `content` field with a docstring pointing at
the Anthropic docs.
3. Message builder. _build_external_messages forwards compaction
parts on both vision and non-vision paths; the per-provider
stream helper decides whether to forward to the wire (Anthropic
does; other providers ignore the part). When a non-vision route
ends up with a single text part, collapse back to a string
so providers that don't accept content arrays still get the
expected shape.
4. _stream_anthropic outbound translator. {type:"compaction"} parts
on an assistant message land on the wire verbatim. Empty/missing
`content` is skipped so a malformed stored block can't 400
Anthropic.
Tests added (5): stream emits compaction_block tool event with the
summary intact; user-visible content stream does NOT carry the
summary text; outbound body forwards compaction parts verbatim on
the next turn; Pydantic schema accepts the part; builder passes
it through on both vision and non-vision provider routes.
Frontend follow-up: the chat-adapter needs to persist the
compaction_block tool_event onto the stored assistant message so
turn N+1 includes it in payload.messages. Pinned in the PR
description.
Sourcing: https://platform.claude.com/docs/en/build-with-claude/compaction
* [pre-commit.ci] auto fixes from pre-commit.com hooks
for more information, see https://pre-commit.ci
* Address review: gate compaction-part passthrough to Anthropic only
Codex P1: my previous round-trip change preserved {type:"compaction"}
parts on every provider route in _build_external_messages. That
meant a chat history with prior compaction state silently leaked
the Anthropic-specific block to OpenAI/DeepSeek/Mistral/Gemini/
Kimi/OpenRouter on a provider switch, where generic
/chat/completions passthrough hands the unknown content type to
the upstream API and 400s the whole turn.
Added a `provider_type` kwarg to _build_external_messages and
gated the compaction forwarder on `provider_type == "anthropic"`.
Every other value (including the legacy None for callers that
don't pass it yet) strips the part. The Anthropic stream helper
still maps it to a native `compaction` block on the wire.
Threaded provider_type through from _proxy_to_external_provider's
call site.
Tests updated: vision + provider="anthropic" still forwards; six
non-anthropic providers strip the part; missing provider_type
strips defensively; non-vision + anthropic still forwards; non-vision
+ non-anthropic collapses back to a text string.
* [pre-commit.ci] auto fixes from pre-commit.com hooks
for more information, see https://pre-commit.ci
---------
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
* Studio: wire Anthropic web_fetch server-side tool
Studio's Anthropic passthrough only forwarded web_search and
code_execution when enabled_tools was set. Asking Claude through Studio
to fetch a URL produced no fetch (the tool was not in the outbound
tools array), so users had to fall back to web_search even when they
already had the exact URL they wanted.
This change opts in web_fetch_20250910 when enabled_tools contains
"web_fetch". The new tool entry is appended alongside any existing
web_search / code_execution entries:
{"type": "web_fetch_20250910", "name": "web_fetch", "max_uses": 5}
No anthropic-beta header is required (web_fetch is GA); the existing
code-execution-2025-08-25 flag continues to merge cleanly when both
tools are enabled in the same turn.
SSE translation mirrors the web_search path. A `server_tool_use` block
with name="web_fetch" emits a `tool_start` _toolEvent carrying the
URL the model asked to fetch; the matching `web_fetch_tool_result`
block emits a `tool_end` _toolEvent whose result string follows the
Title / URL / Snippet shape parseSourcesFromResult on the frontend
already expects, so the source pill renders identically. Error blocks
(`web_fetch_tool_error`) are surfaced as "Error: <error_code>" matching
the code_execution error path.
The final "Anthropic stream complete" log line picks up web_fetch_
requested / web_fetch_invocations / web_fetch_urls so support reports
of "the model did not fetch anything" can be triaged from the log.
Verified end to end against claude-haiku-4-5 with
`enabled_tools=["web_fetch"]`: the model emitted tool_start with
url=https://example.com and tool_end with the page Title + URL +
Snippet, plus the assistant message correctly read back "Example
Domain" as the title.
Tests:
- 5 new unit tests in test_anthropic_web_fetch.py covering tool
registration, the combined web_search + web_fetch + code_execution
request body, the pill-off case, and SSE translation for both
success and error paths.
- All 242 existing Anthropic + OpenAI provider tests still pass.
The enabled_tools field description in models/inference.py is updated
so OpenAPI consumers see the new option.
* [pre-commit.ci] auto fixes from pre-commit.com hooks
for more information, see https://pre-commit.ci
* web_fetch: title fallback to URL, log parse failures, drop dead checks
Three review nits on the previous commit:
1. `_format_web_fetch_result` left `title` empty when Anthropic omitted
`document.title`. The frontend `parseSourcesFromResult` only emits
a source pill when both `Title:` and `URL:` lines are present, so
fetches against pages without an HTML title tag silently lost
their citation in the UI. Fall back to `title = title or url`,
matching the web_search formatter.
2. The broad `except Exception` around `json.loads(buffer)` for the
web_fetch input swallowed the failure with no trace. Log at debug
so a malformed partial_json buffer can be triaged from the server
log without changing behavior.
3. `inner` was already sanitised to a dict at the matching
content_block_start and `_format_web_fetch_result` always returns
a non-empty string (defaulting to "(fetch complete)"), so the
`isinstance(inner, dict) else {}` guard and the
`result_text or "(fetch complete)"` fallback at the emit site
were dead code. Removed.
Added a test exercising the titleless path so the fallback stays
covered.
* chat-adapter: emit source pills for web_fetch tool calls
`parseSourcesFromResult` was only wired up for tool calls where
`toolName === "web_search"`, so the Title / URL / Snippet block the
backend formatter emits for `web_fetch_tool_result` never reached the
source-pill renderer. Users saw the raw tool result in the tool card
but the dedicated source-pill row at the message tail stayed empty.
Both web_search and web_fetch ship the same text shape today, so the
fix is to broaden the gate.
* Address review: wire web_fetch from Search pill + fix pause_turn truncation
Two reviewer follow-ups on the Anthropic web_fetch PR:
1. The backend tool wiring landed but the frontend chat-adapter
never put `web_fetch` in `enabled_tools`, so toggling the Search
pill only ever attached `web_search` -- web_fetch was unreachable
from the UI. Added providerSupportsBuiltinWebFetch() (Anthropic
today) and paired the entry with the existing Search pill, since
the canonical workflow is "search returns URLs, fetch reads
them" and there is no separate UI toggle yet.
2. `pause_turn` from Anthropic's stop_reason vocabulary fell through
the finish_reason map's "stop" default, which the OpenAI-format
client renders as end-of-message and truncates the answer. Per
the docs pause_turn means "Claude paused a long server-tool
turn (web_search / web_fetch) and will resume". Mapped to None
and skipped the chunk emission so the SSE stream still ends with
[DONE] on message_stop but no terminal finish_reason lands on
the client. While there: added explicit mappings for `tool_use`
(-> tool_calls) and `refusal` (-> content_filter) which were
also falling through to "stop".
Tests added: pause_turn emits no finish_reason, end_turn still
emits "stop", refusal maps to "content_filter".
Sourcing: https://platform.claude.com/docs/en/api/messages#response-stop-reason
---------
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Daniel Han