What changed technically

Larger context windows and tool use. An assistant that can read many files, run tests and act on the results is doing something categorically different from completing a line.

Where teams report real gains

Consistently:

  • Writing tests for existing code
  • Migrations and mechanical refactors
  • Explaining unfamiliar codebases
  • First-draft documentation

The unchanged part

Review. Generated code compiles and looks plausible far more often than it is correct, which makes careful review more important rather than less.