Pydantic Pydantic TzInfo(UTC) != datetime.UTC (Fix)

The Fix

pip install pydantic==1.10.1

Based on closed pydantic/pydantic issue #8683 · PR/commit linked

Jump to Verify Open PR/Commit

@@ -7,7 +7,7 @@ isort==4.3.21
 pycodestyle==2.5.0
 pyflakes==2.1.1
-pytest==5.3.4
+pytest==5.3.5
 pytest-cov==2.8.1

repro.py

import datetime

from pydantic import BaseModel


class Event(BaseModel):
    dt: datetime.datetime = None


event = Event(dt="2024-01-01T13:56:57.115Z")
print("This should be True:", event.dt.tzinfo == datetime.UTC)
# prints: This should be True: False

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==1.10.1\nWhen NOT to use: This fix should not be applied if relying on custom timezone comparisons.\n\n

Why This Fix Works in Production

Trigger: A Pydantic model with a `datetime.datetime` attribute and initialized with an UTC timestamp fails to correctly compare its `.tzinfo` attribute to…
Mechanism: Addresses the issue of incorrect comparison of Pydantic's TzInfo with datetime.UTC by implementing necessary equality checks.
Why the fix works: Addresses the issue of incorrect comparison of Pydantic's TzInfo with datetime.UTC by implementing necessary equality checks. (first fixed release: 1.10.1).

Production impact:

If left unfixed, this can cause silent data inconsistencies that propagate (bad cache entries, incorrect downstream decisions).

Why This Breaks in Prod

Shows up under Python 3.11 in real deployments (not just unit tests).
Production symptom (often without a traceback): A Pydantic model with a `datetime.datetime` attribute and initialized with an UTC timestamp fails to correctly compare its `.tzinfo` attribute to `datetime.UTC` for equality.

Proof / Evidence

GitHub issue: #8683
Fix PR: https://github.com/pydantic/pydantic-core/pull/1197
First fixed release: 1.10.1
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.61

Discussion

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

Jump to Sources Open on GitHub

“@gkoller, Thanks for reporting this”

@sydney-runkle · 2024-02-02 · source

“don't we just need to fix TzInfo::__richcmp__?”

@samuelcolvin · 2024-02-02 · source

“We could definitely implement comparisons for pydantic_core.TzInfo with fixed-offset datetime.timezone, which I think would fix the UTC case”

@davidhewitt · 2024-02-02 · source

“Note that Python’s own standard library has many different UTC zone objects: for example, datetime.UTC, zoneinfo.ZoneInfo("UCT"), zoneinfo.ZoneInfo("UTC"), zoneinfo.ZoneInfo("Universal"), zoneinfo.ZoneInfo("Zulu"), zoneinfo.ZoneInfo("Etc/UCT"), zoneinfo.ZoneIn”

@andersk · 2024-02-02 · source

Failure Signature (Search String)

A Pydantic model with a `datetime.datetime` attribute and initialized with an UTC timestamp fails to correctly compare its `.tzinfo` attribute to `datetime.UTC` for equality.
Though It is a change in behaviour from Pydantic V1 to V2 and probably should be documented as such somewhere in the [Migration Guide](https://docs.pydantic.dev/latest/migration).

Copy-friendly signature

signature.txt

Failure Signature
-----------------
A Pydantic model with a `datetime.datetime` attribute and initialized with an UTC timestamp fails to correctly compare its `.tzinfo` attribute to `datetime.UTC` for equality.
Though It is a change in behaviour from Pydantic V1 to V2 and probably should be documented as such somewhere in the [Migration Guide](https://docs.pydantic.dev/latest/migration).

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
A Pydantic model with a `datetime.datetime` attribute and initialized with an UTC timestamp fails to correctly compare its `.tzinfo` attribute to `datetime.UTC` for equality.
Though It is a change in behaviour from Pydantic V1 to V2 and probably should be documented as such somewhere in the [Migration Guide](https://docs.pydantic.dev/latest/migration).

Minimal Reproduction

repro.py

import datetime

from pydantic import BaseModel


class Event(BaseModel):
    dt: datetime.datetime = None


event = Event(dt="2024-01-01T13:56:57.115Z")
print("This should be True:", event.dt.tzinfo == datetime.UTC)
# prints: This should be True: False

Environment

Python: 3.11
Pydantic: 2

What Broke

Comparisons of datetime objects with UTC timestamps fail, leading to incorrect behavior.

Fix Options (Details)

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

pip install pydantic==1.10.1

When NOT to use: This fix should not be applied if relying on custom timezone comparisons.

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

Fix reference: https://github.com/pydantic/pydantic-core/pull/1197

First fixed release: 1.10.1

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

When NOT to Use This Fix

This fix should not be applied if relying on custom timezone comparisons.

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
1.10.1	Fixed

Related Issues

No related fixes found.

Cluster: pydantic:data-consistency Pydantic hub Pydantic best practices All hubs All clusters

Related clusters: Configuration error OpenAPI schema Serialization

Sources

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