Since version 3.0.0 Yii adopts SemVer versioning to achieve better predictability and compatibility with Composer.

Same will happen with extensions. They will adopt SemVer starting from next major versions.

SemVer is simple. Given a version number MAJOR.MINOR.PATCH, increment the:

• MAJOR version when you make incompatible API changes,
• MINOR version when you add functionality in a backwards-compatible manner, and
• PATCH version when you make backwards-compatible bug fixes.

Yii 2.0.x versioning stays as is.