Query Transformations When to Apply | Technique | Recall Gain | Latency Cost | Best For | |---|---|---|---| | Multi-query | +10-20% | 1 LLM call | Ambiguous or short queries | | HyDE | +5-15% | 1 LLM call | Specialized domains, terminology mismatch | | Step-back | +5-10% | 1 LLM call | Detail-heavy questions | | RAG-fusion | +15-25% | 1 LLM + N searches | General-purpose quality boost | | Sub-query decomposition | +20-30% on multi-hop | 1 LLM + N retrievals | Multi-part questions | | Query routing | Varies | 1 classifier call | Heterogeneous indexes | | Expansion (synonyms) | +5% | Free-ish |…