Those of you who routinely apply all plugin updates may already have noticed that the version numbers of the plugins in the Pipeline suite have switched to a 2.x scheme. Besides aligning better with the upcoming Jenkins 2.0 core release, the plugins are now being released with independent lifecycles.
“Pipeline 1.15” (the last in the 1.x line) included simultaneous releases of a dozen or so plugins with the 1.15 version number (and 1.15+ dependencies on each other). All these plugins were built out of a single workflow-plugin repository. While that was convenient in the early days for prototyping wide-ranging changes, it has become an encumbrance now that the Pipeline code is fairly mature, and more people are experimenting with additions and patches.
As of 2.0, all the plugins in the system live in their own repositories on GitHub—named to match the plugin code name, which in most cases uses the historical workflow term, so for example workflow-job-plugin. Some complex steps were moved into their own plugins, such as pipeline-build-step-plugin. The 1.x changelog is closed; now each plugin keeps a changelog in its own wiki, for example here for the Pipeline Job plugin.
Among other benefits, this change makes it easier to cut new plugin releases for even minor bug fixes or enhancements, or for developers to experiment with patches to certain plugins. It also opens the door for the “aggregator” plugin (called simply Pipeline) to pull in dependencies on other plugins that seem broadly valuable, like the stage view.
The original repository has been renamed pipeline-plugin and for now still holds some documentation, which might later be moved to jenkins.io.
You need not do anything special to “move” to the 2.x line; 1.642.x and later users can just accept all Pipeline-related plugin updates. Note that if you update Pipeline Supporting APIs you must update Pipeline, or at least install/update some related plugins as noted in the wiki.