We strive to keep JRuby as backward-compatible as possible, but deprecations are inevitable. Our policy is similar to other projects:

• At least one major release with a deprecation in place, providing a migration path to eliminate the warning and move to a non-deprecated alternative.
• Removal of deprecated behavior only after a sufficient amount of time has passed, like one major version with deprecated legacy behavior.

We use the deprecated label in our issue tracker to mark all issues related to deprecation (both adding the deprecation and eventually changing or removing the feature):

Deprecation-related issues and pull requests