# What changed in fastapi > 49 changes in fastapi 0.129 to 0.143 from its official release notes, upgrade guides and advisories: 9 breaking, 2 deprecations, 12 new APIs and options. Each one cited. Sources checked 2026-10-17. HTML: https://unstale.sh/pypi/fastapi/ To see which of these apply to a repository, run `npx @unstale/cli init` in it. ## fastapi 0.143 ### Breaking changes - Set this environment variable to true to retain automatic OpenTelemetry exporter setup from OTEL_* environment variables. (0.143.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.143.0) - Set auto_configure to true in the FastAPI telemetry configuration to retain automatic OpenTelemetry exporter setup. (0.143.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.143.0) ### Fixes and other changes - Fixes serialization of non-finite floats in JSONL and SSE streams. (0.143.3) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.143.3) - Fixes blocking frontend fallback file checks. (0.143.2) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.143.2) - Fixes included route metadata in iter_route_contexts(). (0.143.1) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.143.1) ## fastapi 0.142 ### New APIs and options - FastAPI adds native OpenTelemetry support. (0.142.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.142.0) ### Fixes and other changes - FastAPI telemetry is isolated for excluded requests. (0.142.4) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.142.4) - Cache OpenTelemetry tracers to preserve warning deduplication. (0.142.3) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.142.3) - Startup is allowed to continue when automatic OpenTelemetry configuration fails. (0.142.2) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.142.2) - Fixes repeated endpoint wrapping in included routers. (0.142.1) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.142.1) ## fastapi 0.141 ### New APIs and options - Adds app.frontend with check_dir="auto" to make local development more convenient with fastapi dev. (0.141.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.141.0) ### Fixes and other changes - Fix support for background tasks and headers from dependencies in `app.frontend()`. (0.141.1) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.141.1) ## fastapi 0.140 ### Performance - Reduced memory usage in dependencies, which may lower FastAPI’s runtime memory consumption. (0.140.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.140.0) ### Fixes and other changes - Fixes `status_code` being ignored for SSE and JSONL streaming endpoints. (0.140.13) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.140.13) - Fixes line splitting to comply with the SSE spec. (0.140.12) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.140.12) - Fixes response_model_* parameters being ignored for non-generator endpoints with Iterable return types. (0.140.11) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.140.11) - Fix handling sequences with nested Annotated types. (0.140.10) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.140.10) - Fixes `exclude_defaults` not being propagated to dictionary keys and values during encoding. (0.140.9) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.140.9) - Fixes the stream item type being lost when using include_router(). (0.140.8) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.140.8) ## fastapi 0.139 ### New APIs and options - app.frontend() now supports dependencies, for example to enable automatic cookie authentication for the frontend. (0.139.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.139.0) ### Fixes and other changes - Router route building is thread-safe, mainly benefiting tests running in parallel threads. (0.139.2) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.139.2) - Frontend fallback now supports dotted paths such as /users/john.doe. (0.139.1) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.139.1) ## fastapi 0.138 ### Breaking changes - Returns 404 for methods other than GET or HEAD when there are no static file matches. (0.138.2) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.138.2) ### New APIs and options - Adds support for serving a frontend from a directory using app.frontend, allowing developers to configure the frontend at a path such as /. (0.138.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.138.0) - Adds support for serving a frontend from a directory using router.frontend, allowing developers to configure the frontend at a path such as /. (0.138.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.138.0) ## fastapi 0.137 ### Breaking changes - router.routes can now contain intermediate objects forming a tree, not just APIRoute objects; treat it as an internal implementation detail rather than iterating or modifying it as a flat list. (0.137.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.137.0) ### New APIs and options - Adds iter_route_contexts() for advanced use cases that previously used router.routes. (0.137.2) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.137.2) - APIRouter adds an experimental handle method, allowing a router to customize how it handles requests. (0.137.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.137.0) - APIRouter adds an experimental matches method, allowing a router to customize how it matches requests, such as matching on a specific header. (0.137.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.137.0) ### Behavior and default changes - APIRouter instances are preserved when included instead of having their routes copied, enabling router customization and saving memory in some cases. (0.137.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.137.0) - Included routers and routes are no longer copied, so routes added after inclusion are reflected, and a subrouter can be included before its routes are added. (0.137.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.137.0) ### Fixes and other changes - Typing checks for APIRoute are fixed. (0.137.1) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.137.1) - Path operations in a prefixless router now allow an empty path. (0.137.1) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.137.1) ## fastapi 0.136 ### Breaking changes - With the default convert_underscores=True, underscore headers are no longer accepted. (0.136.3) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.136.3) ### Fixes and other changes - Server Sent Event fields are validated to prevent applications from sending broken data. (0.136.2) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.136.2) - FastAPI supports free-threaded Python 3.14t. (0.136.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.136.0) ## fastapi 0.135 ### Breaking changes - The April Fool's @app.vibe() decorator was removed. (0.135.4) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.135.4) - The minimum supported Pydantic version is now 2.9.0, affecting which versions can be installed with FastAPI. (0.135.2) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.135.2) ### New APIs and options - Adds support for the @app.vibe() decorator. (0.135.3) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.135.3) - FastAPI adds support for Server-Sent Events (SSE). (0.135.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.135.0) ### Fixes and other changes - Avoids yielding from a TaskGroup; it is used only as an async context manager and closed in the request async exit stack. (0.135.1) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.135.1) ## fastapi 0.134 ### New APIs and options - Endpoints can stream JSON Lines and binary data with yield. (0.134.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.134.0) ## fastapi 0.133 ### New APIs and options - Adds a FastAPI Agent Skill for use with library agent skills. (0.133.1) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.133.1) ### Behavior and default changes - FastAPI now supports Starlette 1.0.0 and later. (0.133.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.133.0) ## fastapi 0.132 ### Breaking changes - FastAPI now rejects JSON requests without a valid JSON Content-Type header by default; set strict_content_type=False to disable the check. (0.132.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.132.0) ## fastapi 0.131 ### Deprecations - ORJSONResponse is deprecated. (0.131.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.131.0) - UJSONResponse is deprecated. (0.131.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.131.0) ## fastapi 0.130 ### Performance - JSON responses are serialized with Pydantic in Rust when there is a Pydantic return type or response model, resulting in a 2x or greater performance increase. (0.130.0) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.130.0) ## fastapi 0.129 ### Breaking changes - Support for fastapi-slim is dropped and no further versions will be released; use fastapi[standard] or fastapi instead. (0.129.2) — [release notes](https://github.com/fastapi/fastapi/releases/tag/0.129.2)