Anthropic's Claude Code uses custom harness tools over model-level RL tools
Harrison Chase · Everything Gets Rebuilt: The New AI Agent Stack | Harrison Chase, LangChain · Mar 12, 2026 · at 7:55
Harrison Chase is the CEO of LangChain. He analyzes how Anthropic architected Claude Code's harness layer differently from its underlying model capabilities.
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“It doesn't actually use the tools that are RL into the model. So like anthropic models have some like file editing tools. They have a completely different set of tools in, in the actual harness.”
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