Pydantic `TypeAdapter.dump

The Fix

pip install pydantic==2.11.0

Based on closed pydantic/pydantic issue #11408 · 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%.

Jump to Verify Open PR/Commit

@@ -12,6 +12,8 @@
     list: list,
     typing.List: list,  # noqa: UP006
+    tuple: tuple,
+    typing.Tuple: tuple,  # noqa: UP006
     set: set,

repro.py

@pytest.fixture()
def expected_python_dict(self) -> dict[str, list[dict[str, str]]]:
    return {
        "items": [
            {"firstName": "John", "lastName": "Doe"},
            {"firstName": "Mary", "lastName": "Smith"},
        ]
    }

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==2.11.0\nWhen NOT to use: This fix should not be applied if the alias_generator is not intended for use.\n\n

Why This Fix Works in Production

Trigger: assert result == expected_python_dict
Mechanism: The alias_generator was not applied to Sequence[Item] fields when dumping data
Why the fix works: `TypeAdapter.dump_python` and `TypeAdapter.dump_json` now respect `alias_generator` for `Sequence[Item]` fields, fixing the serialization issue. (first fixed release: 2.11.0).

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

Shows up under Python 3.13 in real deployments (not just unit tests).
The alias_generator was not applied to Sequence[Item] fields when dumping data
Production symptom (often without a traceback): assert result == expected_python_dict

Proof / Evidence

GitHub issue: #11408
Fix PR: https://github.com/pydantic/pydantic/pull/11435
First fixed release: 2.11.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.70

Discussion

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

Jump to Sources Open on GitHub

“Thanks for the report @rayansostenes! Looking into this and we'll release a fix in v2.11.”

@sydney-runkle · 2025-02-12 · source

Failure Signature (Search String)

assert result == expected_python_dict

Copy-friendly signature

signature.txt

Failure Signature
-----------------
assert result == expected_python_dict
@pytest.mark.xfail(reason="This test fails, the keys are not in camel case as expected")

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
assert result == expected_python_dict
@pytest.mark.xfail(reason="This test fails, the keys are not in camel case as expected")

Minimal Reproduction

repro.py

@pytest.fixture()
def expected_python_dict(self) -> dict[str, list[dict[str, str]]]:
    return {
        "items": [
            {"firstName": "John", "lastName": "Doe"},
            {"firstName": "Mary", "lastName": "Smith"},
        ]
    }

Environment

Python: 3.13
Pydantic: 2

What Broke

Output JSON keys did not conform to alias generation rules, causing incorrect serialization.

Why It Broke

The alias_generator was not applied to Sequence[Item] fields when dumping data

Fix Options (Details)

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

pip install pydantic==2.11.0

When NOT to use: This fix should not be applied if the alias_generator is not intended for use.

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/11435

First fixed release: 2.11.0

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

When NOT to Use This Fix

This fix should not be applied if the alias_generator is not intended for use.

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
2.11.0	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.

Pydantic `TypeAdapter.dump_python` and `TypeAdapter.dump_json` do not respect `alias_generator` for (Fix)