We're aiming to be 100% compatible with MRI. It's far easier to swap out your runtime than it is to rewrite production code. Of course, situations vary for ever

We're aiming to be 100% compatible with MRI. It's far easier to swap out your runtime than it is to rewrite production code. Of course, situations vary for everyone and each team needs to evaluate on their own. Prior to joining Oracle Labs, I ran a company that went through TechStars (Boston, 2010). We started with Ruby to get the MVP out. I would even say overall it was architected fairly well. But as we started growing, we hit performance issues that we just didn't have with a smaller customer base. As a bootstrapped company trying to grow, putting everything on hold to rewrite subsystems wasn't a terribly appealing option. We finally decided that it was a necessary evil and were going to move from MRI to JRuby, at which point we'd start replacing pieces with Java. As it turns out, JRuby ended up meeting our performance needs and we didn't have to rewrite anything (modulo code changes needed to run on JRuby). I ended up winding that company down for a variety of other reasons, but I'm happy I didn't become another case study in code rewrites.