AI agents underperform in polyrepo environments because they hit three fundamental walls: they can only read one project at a time, cannot land cross-project changes atomically, and lose context across repo boundaries. Monorepos remove these constraints by giving agents full codebase visibility, atomic multi-project writes, and continuous context. Evidence includes Airbnb compressing an 18-month migration to 6 weeks using agents in a monorepo, and a demo showing 4x faster cross-project changes with Nx. For organizations that cannot consolidate into a single repo, Nx introduces Polygraph, a meta-harness that creates a 'synthetic monorepo' by connecting all repos into one dependency graph, orchestrating cross-repo PRs, and providing persistent agent memory across sessions.
