Behind the Scenes: Block 450 JVM Repositories Into Monorepo to Reduce Dependency Drift

Block, Inc. describes migrating ~450 JVM repositories into a monorepo across Cash App and Square engineering to reduce dependency drift and coordination overhead. The system supports ~8,800 weekly builds with ~10 min p90 CI time. The approach improves cross-service changes, build visibility, and developer experience through dependency graph–based builds, selective CI, and custom IDE tooling.