Stable User-Agent Identity in Anthropic’s TypeScript SDK
A focused SDK reliability contribution showing that constructor-derived User-Agent names drift under subclassing or minification. Anthropic closed the PR after shipping the same fix and regression scenario in v0.116.0.
v0.116.0
Anthropic release
51
tests passed
1
focused test file
#1135
public PR
01 · Engineering problem
The failure mode
The SDK generated its User-Agent from constructor.name. Subclassing or JavaScript minification can rename that constructor, producing unstable network identity and weakening observability across builds.
02 · Technical response
What changed
- 01Demonstrated the failure with a subclass whose constructor name differs from the SDK’s canonical identity.
- 02Specified a stable Anthropic/JS versioned token independent of runtime class names.
- 03Added a regression assertion that rejects leaked subclass names while preserving the established header format.
- 04Validated the focused Jest suite, formatting, linting, and TypeScript compilation.
03 · Verified outcome
Evidence, not implication
- ✓Anthropic confirmed the fix shipped in SDK v0.116.0.
- ✓The shipped release included regression coverage for the subclass/minified-name case.
- ✓PR #1135 was closed without merge because upstream had already implemented the same correction.
- ✓The case study is classified as public validation—not a merged contribution.
04 · Public record
Source evidence
Independent engineering and open-source work by Patrick Ribbsaeter / Ribbsaeter Systems. References to maintainers, repositories, or companies identify the public technical context only. No employment, client, vendor, or partnership relationship is implied unless explicitly stated.