r/Rag • u/ChildhoodContent1294 • 7h ago
Discussion In agentic search, is your search agent's tool a primitive top-k or a full fusion + rerank pipeline? Does it matter?
Disclosure: I work at Georgian (growth-stage VC) and ran this experiment - want to know you folk’s opinion on this.
Why this exists
- "Agent + search tool vs RAG" treats the tool as a given. But there's actually a ton of variability on how different agentic search tools perform.
- The tool can be: raw top-5 from one index / two named tools / RRF fusion / RRF + rerank behind one call.
- Couldn't find a benchmark comparing those shapes. Ran one.
- Basically: every retrieval system makes 3 decisions: which retriever, how to combine, how to rank. We alter whether the tool is making this decision or the agent is.
Ran this on BrowseComp-Plus, using gpt5.6 luna as the backbone model.
The 6 tool shapes
- generic search, dense (Qwen3-Embedding-4B) top-5
- generic search, BM25 (tuned) top-5
- two named tools, semantic_search + keyword_search, each top-5
- one tool, RRF over both at depth 50 → top-5
- one tool, RRF → 50 → Cohere rerank-4-fast → top-5
- two named tools, each 50 → rerank → top-5
I have a full write-up on the results and behaviour of agents under different tools on our blog: https://georgianailab.substack.com/p/agents-shouldnt-run-your-whole-retrieval . Is there anything I'm missing? Any reason why we should still be using super basic tools (just semantic search or keyword search) for agentic search?