from pydantic import BaseModel, Field
from typing import List
from typing_extensions import Literal  # not from typing! It's important

class MyModel(BaseModel):
    columns: Literal[['x', 'y', 'z']] =  ['x', 'y', 'z']

Tested on python 3.10, pydantic 2.9.2, typing-extensions 4.12.2