FastAPI 0.142.3 is a maintenance release that focuses on a subtle instrumentation fix plus documentation and localization housekeeping. The headline change addresses how OpenTelemetry tracers are created inside the framework, ensuring that repeated tracer lookups do not interfere with Python's warning deduplication behavior.
- Fix: cache OpenTelemetry tracers so warning deduplication is preserved (
#16468, by@tiangolo). Previously, re-obtaining a tracer on each call could cause the same warning to be re-emitted instead of being deduplicated, producing noisy logs in instrumented apps. - Docs: removed the HTML
titlefrom the newsletter embed to avoid an unwanted tooltip (#16461). - Docs: embedded the FastAPI and friends newsletter signup form directly in the docs (
#16459). - Docs: updated the skill guidance to use
Asyncerfor blocking code executed in threads (#16420). - Translations: updated the
fr,hi,tr,zh,zh-hant,pt,de,uk,ja,ko, andeslocale files with missing entries, generated by@pr-submit[bot].
For developers running FastAPI behind OpenTelemetry-based tracing or APM tooling, the tracer caching fix is the one to care about. Warning deduplication is what keeps repeated deprecation or runtime warnings from flooding logs; if each request path rebuilds a tracer, the interpreter may treat subsequent warnings as distinct and print them again. Caching the tracer keeps instrumentation cheap and keeps logs readable, which matters in high-throughput services where log volume translates directly into cost and noise. The Asyncer documentation note is also worth a look for anyone mixing sync blocking calls with async def endpoints, since offloading blocking work to threads is a common source of event-loop stalls. Translation updates mean localized docs stay aligned with the English source, so non-English readers get current API guidance rather than stale text. Upgrading is a low-risk drop-in for most projects.
Source: https://github.com/fastapi/fastapi/releases/tag/0.142.3