Here's the `comments.py` file for the `app/api/v1/models/` directory of the `blog_app_h23t0` FastAPI backend:

from sqlalchemy import Column, ForeignKey, Integer, String, Text
from app.api.db.database import Base

class Comments(Base):
    __tablename__ = 'comments'

    id = Column(Integer, primary_key=True, index=True)
    post_id = Column(Integer, ForeignKey('posts.id'), nullable=False)
    user_id = Column(Integer, ForeignKey('users.id'), nullable=False)
    comment_text = Column(Text, nullable=False)
    created_at = Column(String, nullable=False)
    updated_at = Column(String, nullable=True)

Explanation:

1. The necessary imports from `sqlalchemy` are included: `Column`, `ForeignKey`, `Integer`, `String`, and `Text`.
5. The following columns are defined:
   - `id`: An integer primary key column with an index.
   - `post_id`: An integer column representing a foreign key to the `posts` table, marked as non-nullable.
   - `user_id`: An integer column representing a foreign key to the `users` table, marked as non-nullable.
   - `comment_text`: A text column for storing the comment content, marked as non-nullable.
   - `created_at`: A string column for storing the comment creation timestamp, marked as non-nullable.
   - `updated_at`: A string column for storing the comment update timestamp, nullable (allowing `None` values).