[core] pydantic basemodel missing values

[tekumara]

What happened + What you expected to happen

pydantic base model instance created inside a remote function is missing values, eg:

❯ python -m raydemo.foo
2025-04-22 20:12:42,548 INFO worker.py:1843 -- Started a local Ray instance. View the dashboard at http://127.0.0.1:8265 
outside=Prediction(key='foo')
(f pid=99091) f: in_f=Prediction()
ray_get=Prediction()

outside is correct but in_f and ray_get shows an empty Prediction() object

Versions / Dependencies

pydantic==2.11.3
pydantic-core==2.33.1
ray==2.44.1

Reproduction script

import ray
from pydantic import BaseModel


class Prediction(BaseModel):
    key: str


ray.init()

outside = Prediction(key="foo")
print(f"{outside=}")

@ray.remote
def f() -> Prediction:
    in_f = Prediction(key="foo")
    print(f"f: {in_f=}")
    return in_f


ray_get = ray.get(f.remote())

print(f"{ray_get=}")

Issue Severity

High: It blocks me from completing my task.

[tekumara]

This looks like a regression introduced by:

pydantic==2.11.0
pydantic-core==2.33.0

As versions pydantic<2.11 are ok.

[zcin]

I bisected it and it seems like this commit, i.e. pydantic-core==2.29.0 is the issue.