FYI, one of the big changes is in integration tests on controllers... it&#x27;s not a huge difference, but if you try to copy from the book instead of generating your controller you might have issues. Also only the 5.1 RC is out.<p>If I was learning, I&#x27;d build an app with the current stable version of 4, a toy crud app with 100% test coverage, then try to convert that to 5. Then compare that to building 5.0 using it&#x27;s generators. You are likely to work with legacy code, so learning 4 is not bad.   May well do that myself, so I&#x27;m catching gotchas like the integration test changes in my toy and not at work on a deadline.<p>But yeah, coding, at least for me, is all about trade offs, and as long as you understand the rails trade offs and mitigations, you are fine.