This concerns the Spring 2019 release 19H1, not Fall 2018 - 1809. It's worth a read because MS has added some performance fixes for the Spectre V2 variant. It will only be available to Win 10 users, not Win 7 or 8. Another incentive to upgrade to 10.

Yes, we have enabled retpoline by default in our 19H1 flights along with what we call "import optimization" to further reduce perf impact due to indirect calls in kernel-mode. Combined, these reduce the perf impact of Spectre v2 mitigations to noise-level for most scenarios.

Mehmet Iyigun (@mamyun) October 18, 2018