Motorola has confirmed which devices will get the Android Oreo update and when they will be getting it. On the company's own blog today it threw together a complete list of phones that are slated to get the update to Google's latest flavor of the operating system, and although it does mention when the update is coming it does so in a rather non-specific way, mentioning only the time frame - this Fall. That means that Motorola device owners will be able to expect the update to come through sometime in the near future, when exactly, at least when it comes to specific dates, is still uncertain.
That said, coming in the near future isn't so bad as Google barely started rolling it out officially to its suite of Nexus and Pixel devices over the past month, so even if Motorola takes the next month or two to roll Oreo out to its entire list of supported devices, it may very well still be ahead of the game compared to other device OEMs. That said it's worth keeping in mind that just because Motorola is committing to pushing out the update this Fall, that doesn't mean Motorola will hit its target for every phone, but also worth considering is that Motorola has had pretty a good track record for updates most of the time.
As far as the supported devices, most of Motorola's recent and current devices from the last two years will be getting the update. This includes the Moto Z, Moto Z Droid, Moto Z Force Droid, Moto Z Play, Moto Z Play Droid, Moto Z2 Play, Moto Z2 Force Edition, Moto X4, Moto G5, Moto G5 Plus, Moto G5S, and the Moto G5S Plus. Absent are devices like the Moto G4 and Moto G4 Plus, which are within the time frame in terms of the Android update life cycle as they were only just released last year, but Motorola explicitly states that the phones mentioned above are the full list of phones to get the update, which means the Moto G4 and Moto G4 Plus will not be getting it. This could always change of course, but owners of the phone shouldn't be expecting it to. If you've got one of the phones listed to receive the update, keep an eye out as it could start rolling out very soon.