Apple ML study compares Retrieve-then-Plan vs Plan-then-Retrieve for LLM agent tool discovery

Apple ML Research · rss · 2026-10-15

Apple ML Research published a scale study of tool discovery architectures for tool-augmented LLM agents. The dominant Retrieve-then-Plan (RtP) paradigm embeds the user query and retrieves similar tools via approximate nearest-neighbor search from large API registries, since finite context windows can't fit all tool definitions.

The study evaluates an alternative Plan-then-Retrieve (PtR) paradigm: the LLM first generates Abstract Tool Stubs — hypothesized function signatures describing the capabilities it needs — which then serve as retrieval queries against the tool registry.

The paper benchmarks both architectures across scales, offering empirical guidance for engineering tool-use in agents.

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