A Responses caller that asked for reasoning summaries got an empty chain
of thought back: every reasoning item carried a signature and no text, so
replaying it produced a Claude thinking block with an empty thinking
field. The cause was the beta list, not the translator. Cloaked requests
always sent redact-thinking-2026-02-12, which makes Anthropic withhold
the summary text even when thinking.display is summarized.
Native Claude Code 2.1.220 treats the two as mutually exclusive: the beta
is only appended while thinking summaries are off, and the request
builder removes it again whenever a display value is attached. An
isolated 2.1.220 profile with showThinkingSummaries enabled confirms it
on the wire, still on cc_entrypoint=cli, sending display=summarized
without the beta and receiving thinking text. A direct A/B against
claude-opus-4-8 pins the effect down: with the beta the thinking text is
empty for every display value, without it and with display=summarized the
text comes back. The beta is now dropped whenever the request carries
thinking.display, which is exactly the native rule.
Two translation gaps kept the chain lossy on the way back. redacted_thinking
blocks had no Responses representation at all and vanished, even though
Anthropic requires them to be replayed verbatim; they now ride in
encrypted_content behind a marker prefix and are restored as
redacted_thinking blocks. Reasoning text was only read from summary[],
so a caller whose SDK models the text in content[] lost it; content[] is
now used as a fallback, and only as a fallback so a client that mirrors
both arrays does not replay the text twice.
An item whose encrypted_content is missing or belongs to another provider
is still dropped rather than replayed, because Anthropic rejects a
thinking block without a signature and there is nothing to synthesize.
Derive cache-diagnosis from the final Messages body so cloaked OAuth requests reproduce Claude Code's exact diagnostics trailer instead of receiving an Anthropic 400.
Use advanced-tool-use for OAuth requests with tools and stop synthesizing cache-diagnosis. Two isolated Claude Code 2.1.220 OAuth accounts reproduced the same current profile.
Classify malformed caller metadata and Fast failures as request-scoped, reuse the strict Anthropic origin gate, bound diagnostics and proxy caches, and remove the unrelated translator test change.
Align the remaining measured OAuth wire profiles, including the ordered
connection writer in internal/httpwire that reproduces the observed header
sequence, and the refresh/profile response shapes in internal/auth/claude.
Replay the measured Fast path and keep diagnostic continuity across cloaked and
native requests.
Preserve the native direct token-counting shape so a caller that reaches
count_tokens itself is not reshaped into the cloaked form.
Scope cloak dates to the credential's timezone rather than the host's, so
currentDate matches what the real client would have sent for that account.
CPA negotiates ALPN http/1.1 with Anthropic, so header names are not lowercased
by HPACK and reach the server verbatim. The casing is therefore part of the
fingerprint, and six of the eighteen names CPA emits were wrong because Go
canonicalises everything passed through Header.Set: anthropic-beta,
anthropic-dangerous-direct-browser-access, anthropic-version, x-app,
x-client-request-id and X-Stainless-OS. Writing the map keys directly is the
only way to keep the original casing.
This also fixes ordering at no extra cost. Go sorts header names bytewise when
it serialises a request, and the captured order of the real client is exactly
that same bytewise sort. Host, User-Agent and Content-Length stay misplaced
because Go writes them ahead of the sorted block; a test records that gap and
will fail if it ever closes.
The pass runs at the send boundary rather than inside applyClaudeHeaders: the
rewritten keys are unreachable through Header.Get, and doing it earlier hid
these headers from the rest of the pipeline. The boundary is a single
doClaudeUpstreamRequest helper pinned by a structural test, after a mutation
check showed that dropping the call from the streaming path alone was otherwise
undetectable. Expected order is pinned by serialising the request and reading
the header lines back, not by inspecting the header map.
An account without the fast-mode entitlement answers speed:"fast" with HTTP 429
and "Usage credits are required for fast mode." The generic pipeline treats any
429 as quota exhaustion: it marks the credential Quota.Exceeded, assigns an
exponential cooldown up to 30 minutes and rotates to the next credential, so a
single request could walk and cool down the entire Claude pool over a
capability the account will never have.
Classify it through the existing RequestScopedError contract instead, which
already suppresses cooldown, rotation and retry. The status and body are then
returned verbatim: the classifier exists to stop the generic pipeline from
handling the error, not to handle it.
Detection deliberately requires both "fast mode" and a credits phrase, so a
genuine rate limit, which never mentions fast mode, keeps its cooldown. Tests
cover both observed wordings, byte-exact pass-through, and the negative cases.
Claude Code builds Anthropic-Beta per request instead of sending a fixed list.
Captured from an isolated 2.1.220 profile pointed at api.anthropic.com through
a local proxy, over two rounds covering 11 model IDs and the [1m] variants:
constant claude-code, interleaved-thinking, redact-thinking,
thinking-token-count, context-management, prompt-caching-scope
tools advanced-tool-use-2025-11-20 only when tools are declared
model mid-conversation-system-2026-04-07 only on models that accept a
role=system turn
[1m] context-1m-2025-08-07, directly after claude-code-20250219 rather
than at the end
trailing effort-2025-11-24, then server-side-fallback-2026-06-01
claude-sonnet-5 emits mid-conversation-system-2026-04-07, so it accepts a
role=system turn and must not sit in the legacy reminder whitelist.
count_tokens does not reuse the inference fingerprint. Running /context in an
interactive session issues 37 identical calls, which made the endpoint
observable for the first time: four betas only, and 21 headers rather than 22
because X-Stainless-Timeout is absent. The profile is selected from the request
path so no call site has to thread another flag.
Keep the opaque MCP alias reversible and meaning-preserving so a cloaked
caller's tool declarations, choices and history survive the round trip without
changing tool ownership.
Detect confirmed CLI, sdk-cli and VSCode callers before mutation so native
software, system, tool, cache and beta shapes pass through, while unconfirmed
OAuth clients receive a coherent minimum CLI identity.
Persist each Claude OAuth credential's upstream account metadata and one stable
device ID, derive one stable session per agent conversation, and keep body and
header identity synchronized across Messages, streaming and count_tokens.
Alias every cloaked third-party custom tool through caller-stable opaque MCP
names and restore declarations, choices, history, references, non-stream
responses and SSE events without changing tool ownership.
Implement the Claude Code 2.1.220 CCH algorithm over the final serialized
request bytes, align currentDate and first-user cache layout, update the
official beta/header baseline, and use upstream count_tokens for OAuth and
first-party Anthropic credentials.
Match the 2.1.220 TLS ClientHello so the transport fingerprint agrees with the
identity the request now claims, and document the CLI defaults and automatic
OAuth signing / tool alias behaviour in config.example.yaml.
- Introduced `claudeFastModeBeta` constant and logic to append it conditionally based on the `speed` attribute in the request body.
- Ensured `fast-mode-2026-02-01` beta inclusion only when explicitly requested or if the `speed` is set to `fast`.
- Updated `applyClaudeHeaders` to dynamically handle fast-mode beta and adjust headers accordingly.
- Enhanced beta extraction and addition with a new helper `appendClaudeFastModeBeta`.
- Improved flexibility in beta handling by preserving requested overrides while ensuring compatibility with default configurations.
Closes: #4703
- Removed deprecated interceptor and executor-related methods, including `callRequestInterceptor`, `callResponseInterceptor`, and `callStreamChunkInterceptor`.
- Consolidated unused logic and pruned redundant imports to streamline `adapters.go`.
- No functional changes.
