JRuby 9000 is the current major version of JRuby. It is compatible with (MRI) Ruby interpreters 2.2, 2.3 and 2.5. JRuby 9000 was the first major release where we had nontrivial breaking changes along with new features. It was our chance to clean things up that had lingered for years. JRuby 9.0.0.0 was released July 22nd, 2015.

"The unusual version name came about as the team realized the next natural JRuby version would be either 1.8 or 2.0 and thus decided to avoid confusion with the Ruby MRI versions by using 9000." (ref: infoq.com article summarizing @headius talk at Baruco)

• JRuby 9.4 Ruby 3.1 compatible, currently supported version

All users should start with or upgrade to 9.4. We will provide support for at least one year after the next version is released.

• JRuby 9.3 Ruby 2.6 compatible, community-driven support (we'll fix or backport fixes with user help)

The following versions are unsupported but still in use by many users. We recommend upgrading to 9.4.

• JRuby 9.1 Ruby 2.3 compatible, no longer supported
• JRuby 9.2 Ruby 2.5 compatible, no longer supported
• JRuby 9.0 Ruby 2.2 compatible, no longer supported