Query an instrumentedattribute by its length in SQLAlchemy

Question

The way the database is setup is like this. I'm using SQLModel, but underneath it's SQLAlchemy.

class Paper(SQLModel, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
        similar: List["PaperSimilarLink"] = Relationship(
        link_model=PaperSimilarLink,
        back_populates="similar",
        sa_relationship_kwargs=dict(
            primaryjoin="Paper.id==PaperSimilarLink.paper_id",
            secondaryjoin="Paper.id==PaperSimilarLink.similar_id",
        ),
    )

class PaperSimilarLink(SQLModel, table=True):
    paper_id: int = Field(default=None, foreign_key="paper.id", primary_key=True)
    similar_id: int = Field(default=None, foreign_key="paper.id", primary_key=True)
    paper: "Paper" = Relationship(
        back_populates="similar",
        sa_relationship_kwargs=dict(
            foreign_keys="[PaperSimilarLink.paper_id]",
        ),
    )
    similar: "Paper" = Relationship(
        back_populates="similar",
        sa_relationship_kwargs=dict(
            foreign_keys="[PaperSimilarLink.similar_id]",
        ),
    )
    similarity: Optional[float]

The query I am looking for is to look for all the Paper objects that have less than x number of PaperSimilarLinks located at Paper.similar. I've tried this:

papers = session.exec(select(Paper).where(Paper.similar.count() <= 11)).all()

It errors me out saying AttributeError: Neither 'InstrumentedAttribute' object nor 'Comparator' object associated with Paper.similar has an attribute 'count'

I figured this was a very simple query, but it's illuding me! How would I do this?