The Fix
pip install pydantic==1.10.17
Based on closed pydantic/pydantic issue #9691 · PR/commit linked
Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.
@@ -1154,14 +1154,18 @@ Fields are defined by one of the following tuple forms:
Using a `Field(...)` call as the second argument in the tuple (the default value)
-allows for more advanced field configuration. It's analogous to doing the following
-with a standard `BaseModel`:
+allows for more advanced field configuration. Thus, the following are analogous:
from pydantic import Field, create_model
from pydantic.fields import FieldInfo
config: dict[str, tuple[type, FieldInfo]] = {
"some_field": (int, Field(default=5, description="Some description."))
}
Model = create_model("Model", **config)
Re-run the minimal reproduction on your broken version, then apply the fix and re-run.
Option A — Upgrade to fixed release\npip install pydantic==1.10.17\nWhen NOT to use: This fix is not applicable if you do not need to document field descriptions.\n\n
Why This Fix Works in Production
- Trigger: When run with `mypy==1.10.0`, will error:
- Mechanism: The documentation for `create_model` did not include an example using `Field` with descriptions
- Why the fix works: Updates the documentation for dynamic models in Pydantic, providing an example of using `create_model` with `Field` to include descriptions. (first fixed release: 1.10.17).
- 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 documentation for `create_model` did not include an example using `Field` with descriptions
- Production symptom (often without a traceback): When run with `mypy==1.10.0`, will error:
Proof / Evidence
- GitHub issue: #9691
- Fix PR: https://github.com/pydantic/pydantic/pull/9695
- First fixed release: 1.10.17
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.85
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.65
Verified Execution
We executed the runnable minimal repro in a temporary environment and captured exit codes + logs.
- Status: PASS
- Ran: 2026-02-11T16:52:29Z
- Package: pydantic
- Fixed: 1.10.17
- Mode: fixed_only
- Outcome: ok
Logs
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“Hi @jamesbraza, We just use Any as the type of the field definitions and enforce that the appropriate information is present at runtime. Pyright doesn't…”
“I've added a PR with an extra note / example.”
Failure Signature (Search String)
- When run with `mypy==1.10.0`, will error:
- a.py:5:5: error: Dict entry 0 has incompatible type "str":
Copy-friendly signature
Failure Signature
-----------------
When run with `mypy==1.10.0`, will error:
a.py:5:5: error: Dict entry 0 has incompatible type "str":
Error Message
Signature-only (no traceback captured)
Error Message
-------------
When run with `mypy==1.10.0`, will error:
a.py:5:5: error: Dict entry 0 has incompatible type "str":
Minimal Reproduction
from pydantic import Field, create_model
from pydantic.fields import FieldInfo
config: dict[str, tuple[type, FieldInfo]] = {
"some_field": (int, Field(default=5, description="Some description."))
}
Model = create_model("Model", **config)
What Broke
Users encountered type errors when using `create_model` with `Field` descriptions.
Why It Broke
The documentation for `create_model` did not include an example using `Field` with descriptions
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install pydantic==1.10.17
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)
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)
Fix reference: https://github.com/pydantic/pydantic/pull/9695
First fixed release: 1.10.17
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- This fix is not applicable if you do not need to document field descriptions.
- 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.
Verify Fix
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 |
|---|---|
| 1.10.17 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.