K8s 1.6 was released on March 28 and GKE made that version available on April 4. I would expect a similar wait time to 1.7.
0 - https://cloud.google.com/container-engine/release-notes#supp...
> There will be no release for the week of July 3rd, since this is a holiday in the US. The next release is planned for the week of July 10th.
> There will be no release for the week of July 3rd, since this is a holiday in the US. The next release is planned for the week of July 10th.