Assistants API: File search returns empty results for PDF files

Sam Okwu
Sam OkwuJan 10, 2026

After uploading PDFs to a vector store, the file search tool returns empty results even for queries that should clearly match the document content.

Steps to reproduce: 1. Create a vector store 2. Upload a PDF file 3. Wait for indexing to complete (status shows completed) 4. Create a thread and run with file_search tool 5. Ask about content that's clearly in the PDF

The same content works fine when uploaded as a .txt file. Something about PDF parsing seems broken.

Anyone else seeing this? Only started happening in the last week or so.

1.8k views11 replies22 likesSolved
2 Replies
Logan K.
Logan K.StaffAccepted AnswerJan 12

Temperature 0 with the same seed should give mostly deterministic results, but there are two caveats:

1. System fingerprint changes: When we update the model infrastructure, the fingerprint changes and outputs may differ 2. Server-side batching: Non-determinism can occur due to floating-point arithmetic in parallel processing

For maximum reproducibility, check that system_fingerprint matches across calls. If it differs, the model backend was updated.

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