At large scale, you still need to have proper API boundaries, even with a monorepo. Otherwise, even with the best tooling, you will never be able to change anyt

At large scale, you still need to have proper API boundaries, even with a monorepo. Otherwise, even with the best tooling, you will never be able to change anything. The APIs are there to ensure the behavior won't change and break anything. In a monorepo, that is easier to check by running all the tests that are affected by your code changes. The actual programming "syntax" is a detail though, and that can be changed (atomically everywhere) anytime with proper tooling. It's only in the old traditional split model that APIs are supposed to be a guarantee for syntax + behavior (+ sometimes ABI).