Pydantic `TypeAdapter` with Union has `Any` type hint

The Fix

pip install pydantic==1.10.16

Based on closed pydantic/pydantic issue #9532 · PR/commit linked

Production note: This usually shows up under retries/timeouts. Treat it as a side-effect risk until you can verify behavior with a canary + real traffic.

Jump to Verify Open PR/Commit

@@ -687,7 +687,7 @@ may need to explicitly specify the generic parameter:
 from pydantic import TypeAdapter
 
-adapter: TypeAdapter[str | int] = TypeAdapter(str | int)
+adapter = TypeAdapter[str | int](str | int)
 ...

repro.py

from pydantic import TypeAdapter

ad1 = TypeAdapter(str | int) # ad1: TypeAdapter[UnionType]
ad2 = TypeAdapter[str | int](str | int) # ad1: TypeAdapter[str | int]

result1 = ad1.validate_python("foo") # result1: UnionType
result2 = ad2.validate_python(42) # result2: str | int

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\npip install pydantic==1.10.16\nWhen NOT to use: Do not use this fix if you require strict type hints without manual annotations.\n\n

Why This Fix Works in Production

Trigger: For most simple error reproduction on command-line and to prove occurence of `Any` type, copy above snippet in `main.py` and invoke `basedpyright` on it (or…
Mechanism: Fixes the typing of `TypeAdapter` to ensure proper type hints for Union types starting from Pydantic 2.7.0.
Why the fix works: Fixes the typing of `TypeAdapter` to ensure proper type hints for Union types starting from Pydantic 2.7.0. (first fixed release: 1.10.16).

Why This Breaks in Prod

Triggered by an upgrade/regression window: 2.7.0 breaks; 1.10.16 is the first fixed release.
Production symptom (often without a traceback): For most simple error reproduction on command-line and to prove occurence of `Any` type, copy above snippet in `main.py` and invoke `basedpyright` on it (or use IDE of choice with `pyright` and hover over types):

Proof / Evidence

GitHub issue: #9532
Fix PR: https://github.com/pydantic/pydantic/pull/9570
First fixed release: 1.10.16
Affected versions: 2.7.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.59

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“Duplicate of https://github.com/pydantic/pydantic/issues/9147, https://github.com/pydantic/pydantic/discussions/7094 https://discuss.python.org/t/typeform-spelling-for-a-type-annotation-object-at-runtime/51435 is what's needed for TypeAdapter to work with spec”

@Viicos · 2024-05-31 · source

“Hi @Viicos, thanks for mentioning those issues”

@mark-henry01 · 2024-06-01 · source

“> Hi @Viicos, thanks for mentioning those issues”

@Viicos · 2024-06-03 · source

Failure Signature (Search String)

For most simple error reproduction on command-line and to prove occurence of `Any` type, copy above snippet in `main.py` and invoke `basedpyright` on it (or use IDE of choice with
/path/to/proj/main.py:8:1 - error: Type of "result1" is Any (reportAny)

Copy-friendly signature

signature.txt

Failure Signature
-----------------
For most simple error reproduction on command-line and to prove occurence of `Any` type, copy above snippet in `main.py` and invoke `basedpyright` on it (or use IDE of choice with `pyright` and hover over types):
/path/to/proj/main.py:8:1 - error: Type of "result1" is Any (reportAny)

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
For most simple error reproduction on command-line and to prove occurence of `Any` type, copy above snippet in `main.py` and invoke `basedpyright` on it (or use IDE of choice with `pyright` and hover over types):
/path/to/proj/main.py:8:1 - error: Type of "result1" is Any (reportAny)

Minimal Reproduction

repro.py

from pydantic import TypeAdapter

ad1 = TypeAdapter(str | int) # ad1: TypeAdapter[UnionType]
ad2 = TypeAdapter[str | int](str | int) # ad1: TypeAdapter[str | int]

result1 = ad1.validate_python("foo") # result1: UnionType
result2 = ad2.validate_python(42) # result2: str | int

Environment

Pydantic: 2.7.0

What Broke

Type hints for `TypeAdapter` become less specific, leading to IDE errors.

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

pip install pydantic==1.10.16

When NOT to use: Do not use this fix if you require strict type hints without manual annotations.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/pydantic/pydantic/pull/9570

First fixed release: 1.10.16

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

Do not use this fix if you require strict type hints without manual annotations.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Add a CI check that diffs key outputs after upgrades (OpenAPI schema snapshots, JSON payload shapes, CLI output).
Upgrade behind a canary and run integration tests against the canary before 100% rollout.

Version Compatibility Table

Version	Status
2.7.0	Broken
1.10.16	Fixed

Related Issues

No related fixes found.

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Related clusters: Configuration error Data consistency OpenAPI schema

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

Pydantic `TypeAdapter` with Union has `Any` type hint argument starting with Pydantic 2.7.0+ (Fix)