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fix(kosong): omit empty anthropic-beta header when no beta features declared - #2580
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…eclared The Anthropic provider built the anthropic-beta header unconditionally, so once adaptive thinking removed the interleaved-thinking beta the request still carried 'anthropic-beta: ""'. Some backends reject an empty header value. Only set the header when betas are present; user-supplied extra_headers still take precedence.
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Pull request overview
This PR fixes the Anthropic chat provider in Kosong to avoid sending an empty anthropic-beta header when no beta features are declared (notably after adaptive thinking removes the interleaved-thinking beta), and updates tests and changelogs to reflect/cover the behavior.
Changes:
- Only add the
anthropic-betaheader when the effectivebeta_featureslist is non-empty (while preserving user override precedence viaextra_headers). - Tighten/extend API snapshot tests to assert header omission and override semantics.
- Add corresponding changelog entries across the repo and docs.
Reviewed changes
Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.
Show a summary per file
| File | Description |
|---|---|
| packages/kosong/src/kosong/contrib/chat_provider/anthropic.py | Builds extra_headers such that anthropic-beta is omitted when no betas are present. |
| packages/kosong/tests/api_snapshot_tests/test_anthropic.py | Updates adaptive-thinking assertion and adds a new test for empty/override header behavior. |
| packages/kosong/CHANGELOG.md | Notes the Anthropic header omission fix in Kosong’s changelog. |
| docs/zh/release-notes/changelog.md | Adds release note entry (ZH) describing the behavior change. |
| docs/en/release-notes/changelog.md | Adds release note entry (EN) describing the behavior change. |
| CHANGELOG.md | Adds top-level changelog entry for the Kosong fix. |
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| # `anthropic-beta` value is rejected by some backends. | ||
| extra_headers["anthropic-beta"] = ",".join(str(e) for e in betas) | ||
| extra_headers.update(generation_kwargs.pop("extra_headers", {})) |
NLPark-Cran
referenced
this pull request
in NLPark-Cran/cran-code
Aug 18, 2026
Brings kosong 0.56.0 (omit empty anthropic-beta header, #2580/#2581). Conflicts resolved keeping cran-code branding; duplicate definitions from the double-merge artifact removed; test snapshots updated for the 10-attempt retry default; compaction-hook test factory updated for the post-compaction StatusUpdate emission.
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Related Issue
No linked issue — this comes from a verification report against kosong 0.55.0 showing the Anthropic provider still sends an empty
anthropic-betaheader.Description
Problem:
Anthropic._streamed_requestbuilt theanthropic-betaheader unconditionally:When adaptive thinking removes the
interleaved-thinking-2025-05-14beta (Opus 4.6+/Sonnet 4.6+ path inwith_thinking),betasbecomes[]and the request still carriesanthropic-beta: "". An empty header value is rejected or mishandled by some backends/gateways.Fix (
packages/kosong/src/kosong/contrib/chat_provider/anthropic.py): only set theanthropic-betaheader whenbetasis non-empty. Merge precedence is unchanged — user-suppliedextra_headersstill override the generated header, and an explicitly providedanthropic-betainextra_headersis still sent even whenbetasis empty. As a side benefit, an explicitbeta_features=Noneno longer crashesstr.join.Tests (
packages/kosong/tests/api_snapshot_tests/test_anthropic.py):test_anthropic_opus_46_adaptive_thinkingnow asserts the header is absent entirely (previously only checked it didn't contain the interleaved-thinking value).test_anthropic_beta_header_omitted_when_emptycovers: default construction sendsanthropic-beta: interleaved-thinking-2025-05-14; an emptiedbeta_features=[]omits the header; user-suppliedextra_headers={"anthropic-beta": ...}still wins.Changelog entries added to
CHANGELOG.md,packages/kosong/CHANGELOG.md, anddocs/{en,zh}/release-notes/changelog.md.Checklist
make gen-changelogto update the changelog.make gen-docsto update the user documentation.