Actually it's been stable for the last 6 months. No more expected major syntax e.g changes upwards. (apart from parallelism and gc which will be at compiler)
They should really mention that on the website for crystal. I think a lot of people are scared off by seeing the words alpha and breaking changes. Changing those to "beta" and "stable" on the site would help a lot IMO. At the very least calling it stable would be huge.