Why We Stopped Using GitHub Actions 3.0 for Large Monorepos and Moved to Buildkite 2026 Our engineering team manages a 12-million-line monorepo powering core payment infrastructure, with 400+ active developers committing daily. For years, GitHub Actions was our go-to CI/CD tool—until GitHub Actions 3.0 launched in 2025. We adopted it early, expecting improved monorepo support, but hit critical limitations within 3 months that forced a migration to Buildkite by Q1 2026. The Breaking Points with GitHub Actions 3.0 GitHub Actions 3.0 introduced native monorepo orchestration, but it failed to scale for our workload. First, build times ballooned by 400% . The new dependency graph tracking added 12+ minutes to every full build, even with caching. For PR checks, developers waited 25+ minutes for feedback, killing productivity. Second, concurrency limits crushed our workflow . GitHub’s enterprise plan capped concurrent runners at 200 for our tier, but we regularly needed 350+ runners during peak hours (9-11 AM PT).…