Tokenizer Mismatch Bugs in Production RAG (ANSWERED)
Scenario question on cross-model tokenizer bugs — chunk boundaries, context overflow, and embedder vs LLM alignment.
TL;DR — Quick Answer
Tokenizer mismatch occurs when chunking, embedding, and generation use different tokenizers — chunk sizes misalign with LLM context limits, strings split mid-character in CJK, token counts underestimated causing silent truncation, and highlight offsets wrong in citations. Prevent by: chunk by generation model tokenizer (tiktoken); same embedder family where possible; integration tests counting tokens end-to-end; validate retrieved context fits budget with overhead reserved; document model version pairs that must move together.
The Interview Question
What tokenizer mismatch bugs appear in production RAG systems and how do you prevent them?
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