v1.99.0-rc.9 is a pre-release.
It is to help gather feedback from the community and give users a chance to test Kubecost before v1.99 is officially released.
After taking v1.99 for a test drive, if you have any feedback, it would be great if you could open an issue here.
The official change log will come out with the v1.99 release. The estimated release date for v1.99 is Tuesday, December 13.