Why treating subagents as REPL modules changes agent behavior so much

inductionheads · x · 2026-07-22

The post argues that the biggest difference in harness design is whether subagents are treated like simple tool calls or as modules inside a coding REPL. In the RLM-style setup, the LM generates code inside the REPL, and both subagents and other tools live inside that environment.

The author says this small architectural change makes a surprisingly large difference both in what current models can do and in what future models may be able to do with the same setup.

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