APFS will not be supported on Fusion drives upon High Sierra's release. Cuz, well, it's borked on Fusion drives. https://beta.apple.com/sp/betaprogram/apfsfusion Beta versions of macOS High Sierra made a change in the disk format of systems by converting them to use the new Apple File System. The initial release of macOS High Sierra will provide support for the new Apple File System as the default boot filesystem on Mac systems with all-Flash built-in storage. If you installed a beta version of macOS High Sierra, the Fusion Drive in your Mac may have been converted to Apple File System. Because this configuration is not supported in the initial release of macOS High Sierra, we recommend that you follow the steps below to revert back to the previous disk format. Works fine on my 2017 MacBook. I'll be upgrading my 2017 iMac with 1 TB SSD to High Sierra with APFS very soon too. I do note though that the wording leaves it open for APFS to eventually come to Fusion drives at some later date, so there's still hope yet for you Fusion types. Also, I don't know if what happens though if you try to install High Sierra on an iMac where the Fusion drive has been separated into SSD and HD. Anyone want to test?