Y Combinator Ditched All But One Claude Code Tool for 16 of Its Own

Last Updated on August 19, 2026 by Editorial Team Author(s): Chew Loong Nian – AI ENGINEER Originally published on Towards AI. Y Combinator Ditched All But One Claude Code Tool for 16 of Its Own Y Combinator open-sourced the agent harness it runs its own company on. I read the adapter that boots Claude Code inside it, and found one line that takes away almost every tool Claude Code ships with, leaving at most 16 of QM’s own in their place — ten of them unconditional. After identifying the key configuration line that disables nearly all Claude Code built-in tools, the article investigates the QM (Quartermaster) repo to explain what survives and why. The author shows that QM’s “fixed tool surface” is small—ten tools always available and sixteen at maximum—then details how a separate “read-only” mode filters the registry down further. They also walk through QM’s multi-vendor “harness router,” showing how the same underlying QM tool registry is marshaled across different platforms (Claude Code, Codex, OpenCode, and Pi) via multiple adapter transports, and how the system safely resets vendor sessions mid-conversation by storing the transcript in QM’s database. The piece further a…