The release tag client/v8.6.0 is for VolumeSnapshot and VolumeGroupSnapshot APIs and client library which are in a separate go package.

Changes by Kind

API Change

• Promoted VolumeGroupSnapshot API to GA (v1). Updated controllers to use v1 VolumeGroupSnapshot APIs and set v1beta2 as the stored version during migration. (#1368, @xing-yang)

Full Changelog

https://github.com/kubernetes-csi/external-snapshotter/blob/v8.6.0/CHANGELOG/CHANGELOG-8.6.md