New API version for every release?
Drupal 8 has a new versioning system, with the following format:

Major.minor.bugfix

Minor versions are expected every 6 months (8.1.0 was recently released), and will contain backwards compatible enhancements and new features, but will remain compatible with code written for earlier releases of the same major version.

So Drupal 8.1.x contains new features and API enhancements, but remains compatible with modules developed for 8.0.x.

This will allow Drupal to be more agile in future, and new features won't be limited to major releases, but compatibility with modules should be maintained.