Thanks for the details — this is a warning, not a runtime error, but it can fail tests if your test suite treats warnings as errors. What’s happening - pydantic-settings 2.11 introduced a new warning that fires when a settings model sets config keys for TOML-based sources (like

pyproject_toml_table_header

) but has not actually enabled the corresponding source (PyprojectTomlConfigSettingsSource). - Prefect’s settings model historically set those keys even when TOML sources weren’t enabled, which triggers the warning in pydantic-settings 2.11+. - This shows up during imports like

from prefect.testing.utilities import prefect_test_harness

. Status in Prefect - A fix to address pydantic-settings 2.11+ compatibility warnings landed in Prefect 3.4.20. See the release notes: 3.4.20 release notes (item: “Fix pydantic-settings 2.11+ compatibility warnings”, PR #19029). - There’s also related context in this issue where the same warning appears with pydantic-settings 2.11: Prefect logging setup failure with pydantic-settings==2.11. What you can do 1) Verify versions in your environment

python -c "import prefect, pydantic_settings, pydantic; print('prefect', prefect.__version__); print('pydantic-settings', pydantic_settings.__version__); print('pydantic', pydantic.__version__)"

- If Prefect is 3.4.20 and pydantic-settings is 2.11+, you should generally not see this warning anymore. If you still do, it’s harmless, but see options below to silence it. 2) Short-term workarounds if the warning is failing tests - Pin pydantic-settings below 2.11 (this avoids the new warning):

# pip
pip install 'pydantic-settings<2.11'

# poetry
poetry add 'pydantic-settings<2.11'

- Or, silence just this warning in pytest (keeps warnings-as-errors for everything else):

# pytest.ini
[pytest]
filterwarnings =
    ignore:Config key `pyproject_toml_table_header`.*:UserWarning

3) If the warning persists on 3.4.20 - Let me know your exact versions (Prefect, pydantic-settings, Python). There may be an import path in your test harness that triggers the warning before Prefect’s customization takes effect; we can dig into that once we see your env details. Bottom line: It’s a benign warning introduced by pydantic-settings 2.11. Prefect 3.4.20 includes a fix, but if you still see it in tests, pinning pydantic-settings < 2.11 or adding a targeted pytest warning filter will unblock you.

Thanks — that explains it. You’re actually running Prefect 3.4.4, not 3.4.20: - prefect 3.4.4 - pydantic-settings 2.10.1 - pydantic 2.11.7 The fix for these pydantic-settings compatibility warnings landed in Prefect 3.4.20, so 3.4.4 will still emit them. Details: - Release notes: 3.4.20 release notes (item: “Fix pydantic-settings 2.11+ compatibility warnings”, PR #19029) - Related issue for context: Prefect logging setup failure with pydantic-settings==2.11 Why you see it even with pydantic-settings 2.10.1 - The warning is triggered when a model sets config keys for TOML sources (like

pyproject_toml_table_header

) but does not enable the corresponding source. Prefect <3.4.20 set those keys without wiring up the source, so the warning can appear with 2.10.x as well. What to do 1) If possible, upgrade Prefect to 3.4.20+ in the environment where tests run. This removes the warning at the source. - If you expected 3.4.20 already, verify which copy of Prefect your tests import:

python -c "import prefect, sys; print('prefect', prefect.__version__, 'at', prefect.__file__); print('python', sys.executable)"

2) If you can’t upgrade yet, silence just this warning so your tests don’t fail: - Pytest config:

# pytest.ini
   [pytest]
   filterwarnings =
       ignore:Config key `pyproject_toml_table_header`.*:UserWarning
       ignore:Config key `toml_file`.*:UserWarning

- Or very early in tests/conftest.py (before importing Prefect):

import warnings
   warnings.filterwarnings(
       "ignore",
       message=r"Config key `pyproject_toml_table_header`.*",
       category=UserWarning,
   )
   warnings.filterwarnings(
       "ignore",
       message=r"Config key `toml_file`.*",
       category=UserWarning,
   )

If you upgrade to 3.4.20+ and still see the warning, please share the output of the version/location check above and I’ll dig in further.

Yep — that’s the sibling warning to the first one. You can silence it the same way. Add both filters (or a single combined one). In pytest.ini:

[pytest]
filterwarnings =
    ignore:Config key `pyproject_toml_table_header`.*:UserWarning
    ignore:Config key `toml_file`.*:UserWarning

Or, at the very top of tests/conftest.py (before any Prefect imports):

import warnings

warnings.filterwarnings(
    "ignore",
    message=r"Config key `pyproject_toml_table_header`.*",
    category=UserWarning,
)
warnings.filterwarnings(
    "ignore",
    message=r"Config key `toml_file`.*",
    category=UserWarning,
)
# now import Prefect test utilities
from prefect.testing.utilities import prefect_test_harness

If you prefer a single rule:

[pytest]
filterwarnings =
    ignore:Config key `(pyproject_toml_table_header|toml_file)`.*:UserWarning

Longer-term, upgrading to Prefect 3.4.20+ removes these warnings at the source (see 3.4.20 release notes). If you upgrade and still see them, let me know the exact versions and I’ll dig in.

That warning is from Pydantic v2 and means you passed

default=...

to

Field()

in a place where it can’t actually set a field’s default. Common causes: - Putting

Field(default=...)

inside an

Annotated

type alias and then using that alias as a field type - Attaching

Field(default=...)

to just one member of a

Union[...]

In v2, defaults must be attached to the actual model field (via assignment or

Field(default=...)

on the field), not buried in a type alias or a single union branch. Examples of what triggers the warning vs. fixes: Bad (default inside an alias is ignored):

from typing import Annotated
from pydantic import BaseModel, Field

Timezone = Annotated[str, Field(default="UTC", description="time zone")]

class Config(BaseModel):
    tz: Timezone  # warning: default in alias is ignored

Fix 1: keep metadata in the alias, move default to the field assignment:

Timezone = Annotated[str, Field(description="time zone")]

class Config(BaseModel):
    tz: Timezone = "UTC"

Fix 2: apply

Annotated

at the field site:

class Config(BaseModel):
    tz: Annotated[str, Field(default="UTC", description="time zone")]

Union case: Bad (default on just one union member is ignored):

class A(BaseModel): ...
class B(BaseModel): ...

class Config(BaseModel):
    x: Annotated[A, Field(default_factory=A)] | B  # warning

Fix: put the default on the whole field or assign a default value:

class Config(BaseModel):
    x: A | B = Field(default_factory=A)
# or
class Config(BaseModel):
    x: A | B = A(...)

This warning is safe but indicates the default you expected won’t be applied. If this came from a Prefect block/model you wrote, can you share the relevant model field(s) and your Pydantic version? I can suggest the exact change. If it’s from a dependency, you can usually ignore it or filter the warning, but it’s better to correct the model code if you control it.

Short answer: I don’t see a fix for that warning in 3.4.20–3.4.22. It’s still emitted by the server schema’s RRuleSchedule where the timezone default is attached via Field in a context Pydantic v2 ignores. - Source file: prefect/server/schemas/schedules.py - Latest release notes (3.4.22) don’t mention this warning: changelog diff The warning is harmless, but I know it’s noisy. If you want to silence it until we adjust the model: - Via Python

import warnings
from pydantic.warnings import UnsupportedFieldAttributeWarning

warnings.filterwarnings("ignore", category=UnsupportedFieldAttributeWarning)

- Via pytest (pytest.ini)

[pytest]
filterwarnings =
    ignore:The 'default' attribute.*has no effect.*:pydantic.warnings.UnsupportedFieldAttributeWarning

- Via env

PYTHONWARNINGS=ignore::pydantic.warnings.UnsupportedFieldAttributeWarning

If you can share your Prefect and Pydantic versions, I can double-check against that exact combo. If you’d like, I can also open an issue upstream to track moving the default off the Annotated/Field usage in RRuleSchedule.