Library version pydantic 2.9.2, my solution looks like this. I needed json as output.

from pydantic import BaseModel, ConfigDict
from pydantic.alias_generators import to_camel

class WhiteLabel(BaseModel):
    model_config = ConfigDict(alias_generator=to_camel)

    track_id: str
    reg_time: str

test_data = WhiteLabel(
    trackId='test',
    regTime='123'
)

print(test_data.model_dump_json(by_alias=True))

Result

{"trackId":"test","regTime":"123"}