Versioning and API change policy

LensKit strives to maintain a high degree of compatibility, particularly for client code (code using the recommenders).

We define the following use cases:

Client code is code that uses the LensKit APIs and algorithms to provide recommendation services. It does not implement any LensKit interfaces, other than perhaps the DAO.
Implementation code implements various LensKit APIs to provide new algorithms. It may implement individual components of existing algorithms, or reuse their components.
Extension code is level most closely coupled to LensKit’s internals. This is code that derives from the classes inside LensKit algorithm implementations, is closely tied to them (re-implementing particularly internal components, etc.), or extends the evaluator.

LensKit version numbers have three components, Major.Minor.Patch. The versioning is based on Semantic Versioning, adapted for the needs of a framework and toolkit.


LensKit makes no attempt to allow models built and serialized with version 1.x to be read in version 1.y, where x ≠ y. We attempt to keep bug fix releases serialization-compatible, but if a serialization break is necessary to fix a bug, we will break the class (and document such incompatibility in the release notes).


As we develop LensKit, we deprecate methods (and entire classes) from time to time. To preserve backwards compatibility, when these methods appear on “Compatibility: Public” components, they will stick around until the next major release. However, they will be deleted in the next major release. Deprecated methods on more internal/unstable components may be deleted in a subsequent minor release.

Our goal is for all X.0 releases of LensKit to contain no deprecated methods.

Also, if we intend to replace a method with an incompatible method of the same name in the next X.0 release, we we’ll try to make sure that method either changes its signature or gets deprecated in a minor release in advance of the major release. So it’s good, as you update your LensKit-based code, to clear up deprecation warnings when you upgrade to a new LensKit version, but we’ll keep the methods around and working.