Pydantic pydantic.v1 is broken (Fix)

The Fix

pip install pydantic==1.10.16

Based on closed pydantic/pydantic issue #9357 · 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.

Open PR/Commit

@@ -194,10 +194,20 @@ jobs:
       fail-fast: false
       matrix:
-        os: [ubuntu, macos, windows]
+        os: [ubuntu-latest, macos-13, macos-latest, windows-latest]
         python-version: ['3.7', '3.8', '3.9', '3.10']

fix.md

Option A — Upgrade to fixed release\npip install pydantic==1.10.16\nWhen NOT to use: This fix should not be applied if the application relies on specific v1 behavior that may change.\n\n

Why This Fix Works in Production

Trigger: pydantic.v1 is broken
Mechanism: The v1 namespace imports were not fully implemented, causing compatibility issues
Why the fix works: Imports modules and objects directly from the v1 namespace, addressing issues with compatibility in v1.10.15. (first fixed release: 1.10.16).

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 v1 namespace imports were not fully implemented, causing compatibility issues
Production symptom (often without a traceback): pydantic.v1 is broken

Proof / Evidence

GitHub issue: #9357
Fix PR: https://github.com/pydantic/pydantic/pull/9162
First fixed release: 1.10.16
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.76

Discussion

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

Jump to Sources Open on GitHub

“@AngellusMortis, Indeed, looks like things weren't fully implemented there. PR welcome with a fix! This is relatively low priority though, given that it's on the…”

@sydney-runkle · 2024-04-30 · source

“I believe this may be fixed by https://github.com/pydantic/pydantic/pull/9162”

@sydney-runkle · 2024-04-30 · source

“^^ closed by https://github.com/pydantic/pydantic/pull/9162, thanks!”

@sydney-runkle · 2024-06-11 · source

Failure Signature (Search String)

pydantic.v1 is broken
- [X] [Compatibility between releases](https://docs.pydantic.dev/changelog/)

Copy-friendly signature

signature.txt

Failure Signature
-----------------
pydantic.v1 is broken
- [X] [Compatibility between releases](https://docs.pydantic.dev/changelog/)

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
pydantic.v1 is broken
- [X] [Compatibility between releases](https://docs.pydantic.dev/changelog/)

Environment

Pydantic: 1.10.15

Why It Broke

The v1 namespace imports were not fully implemented, causing compatibility issues

Fix Options (Details)

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

pip install pydantic==1.10.16

When NOT to use: This fix should not be applied if the application relies on specific v1 behavior that may change.

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

Option D — Guard side-effects with OnceOnly Guardrail for side-effects

Mitigate duplicate external side-effects under retries/timeouts/agent loops by gating the operation before calling external systems.

Place OnceOnly between your code/agent and real side-effects (Stripe, emails, CRM, APIs).
Use a stable key per side-effect (e.g., customer_id + action + idempotency_key).
Fail-safe: configure fail-open vs fail-closed based on blast radius and spend risk.

Show example snippet (optional)

onceonly.py

from onceonly import OnceOnly
import os

once = OnceOnly(api_key=os.environ["ONCEONLY_API_KEY"], fail_open=True)

# Stable idempotency key per real side-effect.
# Use a request id / job id / webhook delivery id / Stripe event id, etc.
event_id = "evt_..."  # replace
key = f"stripe:webhook:{event_id}"

res = once.check_lock(key=key, ttl=3600)
if res.duplicate:
    return {"status": "already_processed"}

# Safe to execute the side-effect exactly once.
handle_event(event_id)

See OnceOnly SDK

When NOT to use: Do not use this to hide logic bugs or data corruption. Use it to block duplicate external side-effects and enforce tool permissions/spend caps.

Fix reference: https://github.com/pydantic/pydantic/pull/9162

First fixed release: 1.10.16

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

When NOT to Use This Fix

This fix should not be applied if the application relies on specific v1 behavior that may change.
Do not use this to hide logic bugs or data corruption. Use it to block duplicate external side-effects and enforce tool permissions/spend caps.

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
1.10.16	Fixed

Related Issues

No related fixes found.

Cluster: pydantic:configuration-error Pydantic hub Pydantic best practices All hubs All clusters

Related clusters: Data consistency OpenAPI schema Serialization

Sources

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