The forced migration to OpenAI's Assistants API v2 has been a bumpy ride for many engineering teams. While the new File Search tool offers significantly better retrieval accuracy than the deprecated v1 "Retrieval" tool, it has introduced two critical issues: substantial, unexpected monthly costs and persistent "Assistant ID not found" errors during integration. If you recently checked your usage dashboard and saw a spike in "Vector Store" storage fees, or if your application is throwing 404s on Assistants that clearly exist in the dashboard, this guide is for you. The Root Cause: Why v2 is Breaking Your Budget and Builds To fix these issues, we must look at the architectural shift between v1 and v2. The Cost Trap: Orphaned Vector Stores In v1, file retrieval was a "black box." You uploaded a file, attached it to an assistant, and OpenAI handled the indexing. In v2, OpenAI exposed the infrastructure via Vector Stores . A Vector Store is...
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