I faced the same problem. I need to connect to two different databases using, of course, different credentials. I would like to have only one BaseSettings class and reuse it with different env_prefixes.

I came up with a fairly simple solution.

"""Settings"""
from pathlib import Path
from typing import Literal
from pydantic_settings import BaseSettings
from pydantic import Field
from dotenv import load_dotenv


load_dotenv(Path('./.env'))


class DBConnectionSettings(BaseSettings):
    """Database settings for database"""
    def __init__(self, env_prefix: Literal['db_from_', 'db_to_']):
        self.model_config['env_prefix'] = env_prefix
        super().__init__()

    host: str = Field(..., description="Host address of database")
    name: str = Field(..., description="Name of database")
    port: int = Field(3306, description="Port at host")
    driver: str = Field("mysqlconnector", description="Database driver")
    user: str = Field(..., description="Database user name")
    password: str = Field(..., description="Password for db user")


# Call the settings like:
db_from = DBConnectionSettings('db_from_')
print(db_from)
db_to = DBConnectionSettings('db_to_')
print(db_to)

As an example, my .env file is structured as follows:

db_from_host=localhost
db_from_name=db1
db_from_user=user1
db_from_password=secret
db_to_host=localhost
db_to_name=db2
db_to_user=user2
db_to_password=reallyasecret

For your task, the dictionary self.model_config['extra'] can also be set. I suspect this solution is not perfect, as it bypasses any type checking performed by Pydantic's SettingsConfigDict and ConfigDict classes. Please urgently consider this.