See https://github.com/project-open-data/project-open-data.github.io/blob/metadata-v-1.1/catalog.md#version-11-update-

Changes to the common core metadata schema will be reviewed on an ongoing basis. As discussed in /governance, new releases of the schema will only be issued as needed, not more than every 6 months. Suggested changes that alter implementation and structure of the schema will not be merged in-between the regular release cycles.

This Milestone encompasses the transition from version 1.0 to version 1.1.