Pydantic pydantic.errors.PydanticUndefinedAnnotation: name

The Fix

pip install pydantic==2.10.4

Based on closed pydantic/pydantic issue #11076 · 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

@@ -1197,7 +1197,9 @@ except PydanticUserError as exc_info:
 ## Unsupported type for `validate_call` {#validate-call-type}
 
-`validate_call` has some limitations on the callables it can validate. This error is raised when you try to use it with an unsupported callable. Currently the supported callables are functions (including lambdas) and methods and instances of [`partial`][functools.partial]. In the case of [`partial`][functools.partial], the function being partially applied must be one of the supported callables.
+`validate_call` has some limitations on the callables it can validate. This error is raised when you try to use it with an unsupported callable.
+Currently the supported callables are functions (including lambdas, but not built-ins) and methods and instances of [`partial`][functools.partial].

repro.py

from __future__ import annotations

import dataclasses
import typing
import uuid
from datetime import timedelta

import pydantic.dataclasses


@pydantic.dataclasses.dataclass(kw_only=True)
class SqsSendMessageBatchRequestEntry:
    id: str = dataclasses.field(default_factory=lambda: str(uuid.uuid4()))
    delay: timedelta = None
    msg_attrs: dict = dataclasses.field(default_factory=lambda: {})
    msg_sys_attrs: dict = dataclasses.field(default_factory=lambda: {})
    msg_dedupe_id: str = None
    msg_group_id: str = None


@pydantic.validate_call
def sqs_send_message_batch[T: (SqsSendMessageBatchRequestEntry, str, dict)](
        queue_name_or_url: str,
        entries: T|typing.Iterable[T],
):
    pass

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==2.10.4\nWhen NOT to use: This fix should not be applied if the codebase does not utilize PEP 695 type parameters.\n\n

Why This Fix Works in Production

Trigger: pydantic.errors.PydanticUndefinedAnnotation: name 'T' is not defined when using from __future__ import annotations with a genetic function
Mechanism: The error occurs due to improper handling of PEP 695 type parameters in generic functions
Why the fix works: Addresses the issue of PydanticUndefinedAnnotation when using from __future__ import annotations with a generic function. (first fixed release: 2.10.4).

Production impact:

If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.

Why This Breaks in Prod

The error occurs due to improper handling of PEP 695 type parameters in generic functions
Production symptom (often without a traceback): pydantic.errors.PydanticUndefinedAnnotation: name 'T' is not defined when using from __future__ import annotations with a genetic function

Proof / Evidence

GitHub issue: #11076
Fix PR: https://github.com/pydantic/pydantic/pull/11093
First fixed release: 2.10.4
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.43

Discussion

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

Jump to Sources Open on GitHub

“### Initial Checks - [X] I confirm that I'm using Pydantic V2 ### Description Running the below code fails with **pydantic.errors.PydanticUndefinedAnnotation: name 'T' is not defined** It works just fine in 2.9.2, if that helps. ### Example”

Issue thread · issue description · source

Failure Signature (Search String)

pydantic.errors.PydanticUndefinedAnnotation: name 'T' is not defined when using from __future__ import annotations with a genetic function
Running the below code fails with **pydantic.errors.PydanticUndefinedAnnotation: name 'T' is not defined**

Copy-friendly signature

signature.txt

Failure Signature
-----------------
pydantic.errors.PydanticUndefinedAnnotation: name 'T' is not defined when using from __future__ import annotations with a genetic function
Running the below code fails with **pydantic.errors.PydanticUndefinedAnnotation: name 'T' is not defined**

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
pydantic.errors.PydanticUndefinedAnnotation: name 'T' is not defined when using from __future__ import annotations with a genetic function
Running the below code fails with **pydantic.errors.PydanticUndefinedAnnotation: name 'T' is not defined**

Minimal Reproduction

repro.py

from __future__ import annotations

import dataclasses
import typing
import uuid
from datetime import timedelta

import pydantic.dataclasses


@pydantic.dataclasses.dataclass(kw_only=True)
class SqsSendMessageBatchRequestEntry:
    id: str = dataclasses.field(default_factory=lambda: str(uuid.uuid4()))
    delay: timedelta = None
    msg_attrs: dict = dataclasses.field(default_factory=lambda: {})
    msg_sys_attrs: dict = dataclasses.field(default_factory=lambda: {})
    msg_dedupe_id: str = None
    msg_group_id: str = None


@pydantic.validate_call
def sqs_send_message_batch[T: (SqsSendMessageBatchRequestEntry, str, dict)](
        queue_name_or_url: str,
        entries: T|typing.Iterable[T],
):
    pass

Environment

Pydantic: 2

What Broke

Users experience crashes when using generic functions with annotations, leading to application downtime.

Why It Broke

The error occurs due to improper handling of PEP 695 type parameters in generic functions

Fix Options (Details)

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

pip install pydantic==2.10.4

When NOT to use: This fix should not be applied if the codebase does not utilize PEP 695 type parameters.

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/11093

First fixed release: 2.10.4

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

When NOT to Use This Fix

This fix should not be applied if the codebase does not utilize PEP 695 type parameters.

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
2.10.4	Fixed

Related Issues

No related fixes found.

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Related clusters: Data consistency OpenAPI schema Serialization

Sources

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

Pydantic pydantic.errors.PydanticUndefinedAnnotation: name 'T' is not defined when using from (Fix)