Agent-as-a-Tool for Service Providers: Capability Transfer and Token Savings at Scale

As LLM-based agents increasingly rely on external tools, should the tools for a dedicated service be exposed directly to the client agent's LLM (Direct Tool Exposure, DTE), or should they be wrapped behind a capable inner agent to which the client delegates tasks (Agent-as-a-Tool, AaT)? Existing studies predominantly take the client's perspective: given a fixed tool set registered with the client agent, they measure whether multi-agent orchestration improves the client's performance compared with a single LLM orchestrator. On the other hand, no existing study has quantified the benefit from the provider's perspective: what does a client agent gain when a service provider offers a capable agent wrapper as a single registered tool instead of directly exposing all low-level tools? In this paper, we present the first systematic comparison of DTE and AaT from the provider's perspective through a dedicated, controlled experiment. Our central finding is that AaT's benefits are predominantly explained by capability transfer: wrapping tools behind a service agent enables the client agent to draw on the service agent's capabilities, largely independent of the client LLM's own capabilities. In addition, AaT offers a token-efficiency advantage because DTE's token cost grows more sharply as the tool surface scales.