Here's the SQLAlchemy model for the `Book` entity:

```python
from sqlalchemy import Column, String, Text, Integer, ForeignKey
from sqlalchemy.orm import relationship
from sqlalchemy.sql import func
from app.api.db.base_class import Base
import uuid

class Book(Base):
    __tablename__ = "books"

    id = Column(String, primary_key=True, default=lambda: str(uuid.uuid4()))
    title = Column(String, nullable=False, index=True)
    description = Column(Text, nullable=True)
    author = Column(String, nullable=False, index=True)
    pages = Column(Integer, nullable=False)
    
    # Relationships
    # Example: user_id = Column(String, ForeignKey("users.id"))
    # Example: user = relationship("User", back_populates="books")

    # Timestamps
    created_at = Column(DateTime, default=func.now())
    updated_at = Column(DateTime, default=func.now(), onupdate=func.now())
```

This model includes the following columns:

- `id`: A UUID primary key column
- `title`: A required string column for the book title, indexed for faster searches
- `description`: An optional text column for the book description
- `author`: A required string column for the author name, indexed for faster searches
- `pages`: A required integer column for the number of pages

Additionally, the model includes:

- `created_at` and `updated_at` columns for tracking when the record was created and last updated
- Placeholders for relationships to other models (e.g., `User`) if needed

You can customize this model further by adding or modifying columns, constraints, and relationships based on your specific requirements.