“Merging to live” builds and tests all packages that depend on the update.
So for example, building the new JDK to live will build and test all Java packages in previous live, all of them need to pass their package’s tests, only then will the JDK update be “committed into live”.
The only difference is that Google runs all the presubmits / “dry run to live checks” in the CL workflow. Amazon runs them post CL in the “merge VersionSet” workflow.