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$ cat fastapi/week/2026-08-24.log

FastAPI & Pydantic

FastAPI & Pydantic

the week in review · Aug 24 – Aug 30, 2026

Pydantic fixes serializer exclusion bug, preps core speed leap

♥

This week Pydantic shipped a critical serializer fix, advanced a pydantic-core performance overhaul, and refined schema generation, while FastAPI and SQLModel kept pace with CI and dependency updates.

44 commits 36 PRs merged 4 releases 6 briefings covered
fastapi wire → next week →

Pydantic fixed a subtle serializer exclusion bug [1] where the include/exclude filters were dropped when a plain serializer wasn't called, causing serialization to ignore the filters. The serialization now respects the intended field selection in all paths.

A broader performance initiative took shape: schema gathering logic moves to pydantic-core [6], FieldInfo construction gets faster [5], and the build now uses maturin's `--pgo` option [7]. According to the briefings, "Pydantic Core Is Poised For A Speed Leap," driven by these changes.

Pydantic 2.13.5 shipped GC fixes and smart union counting, plus signature reflection now honors `validate_by_alias` [2]. Validation JSON schemas now correctly exclude serialization temporal formats [4] and reflect `str_min_length`/`str_max_length` config [3]. New support for `frozendict` [8] and as defaultdict factories [9] expands type coverage.

FastAPI and SQLModel both bumped `setup-uv` to 10.0.1 [10][11] and Typer to 0.26.1 [12][13], while SQLModel deprecated `min_items` and updated release notes [14].

References

  1. [1] Do not drop include/exclude if serializer wasn't called (#13702) ↗ pydantic/pydantic
  2. [2] Support `populate_by_name` in `@validate_call` ↗ pydantic/pydantic
  3. [3] Reflect `str_min_length` and `str_max_length` config in the JSON schema ↗ pydantic/pydantic
  4. [4] Don't apply serialization temporal formats to validation JSON schemas ↗ pydantic/pydantic
  5. [5] Improve permormance of `FieldInfo` construction ↗ pydantic/pydantic
  6. [6] Move schema gathering logic to `pydantic-core` ↗ pydantic/pydantic
  7. [7] Use maturin `--pgo` option ↗ pydantic/pydantic
  8. [8] Add support for `frozendict` type ↗ pydantic/pydantic
  9. [9] Allow `dict`, `frozendict` and `frozenset` as `defaultdict` default factories ↗ pydantic/pydantic
  10. [10] ⬆️ Bump `setup-uv` action to `10.0.1` ↗ fastapi/fastapi
  11. [11] ⬆️ Bump `setup-uv` action to `10.0.1` ↗ tiangolo/sqlmodel
  12. [12] ⬆️ Bump Typer min version to 0.26.1 ↗ fastapi/fastapi
  13. [13] ⬆️ Bump Typer min version to `0.26.1` ↗ tiangolo/sqlmodel
  14. [14] 📝 Update release notes ↗ tiangolo/sqlmodel

$ ls fastapi/week/ # the briefings behind this review

Tue Aug 25 PYDANTIC FIXES SERIALIZER EXCLUSION BUG Wed Aug 26 CI CACHE GOES DARK ACROSS FASTAPI AND SQLMODEL Thu Aug 27 Pydantic's JSON schema lies to you Fri Aug 28 Pydantic Core Is Poised For A Speed Leap Sat Aug 29 Pydantic 2.13.5 fixes GC, smart union counting; SQLModel deprecates min_items Sun Aug 30 Pydantic signature honors validate_by_alias, GC checks harden core suite
fastapi wire → next week →