A search index's vector field holds embeddings created with text-embedding-3-small (1,536 dimensions). To improve relevance, a developer switches the query code to text-embedding-3-large and passes dimensions=1536 so the query vectors fit the field. Queries now run without errors, but results are close to random. What should the developer do to use the larger model?
Choose one.
Embeddings from different models live in different vector spaces. Matching dimensions alone does not make them comparable.
The trap is the dimensions parameter. text-embedding-3-large can return a shortened 1,536-dimension vector, so the query fits the field and no error appears. But those vectors come from a different model than the stored ones, so distances between them are meaningless. The fix is to embed documents and queries with the same model, which means re-embedding the corpus (and sizing the field for the chosen dimensions). Recall tweaks and reranking operate on top of a broken comparison.
- Notice that the error disappeared but relevance collapsed: a silent mismatch.
- Recall that query and document vectors must come from the same embedding model.
- Recognise that shortening dimensions changes size, not the vector space.
- Pick the option that re-embeds the corpus with the new model.
Exam tip: Changing embedding models means re-embedding the whole corpus; matching dimensions is not enough.
AI-103: Choose Foundry Models, Retrieval Methods and Agent Tools — the lesson that teaches this.