Big news for many people in the U.S. with HTC One M8 phones: Your Android 6.0 Marshmallow update release date has come! But there's one little caveat.

Android 6.0 Marshmallow is finally beginning to roll out to OEM Android handsets in the U.S., after months of preparation and waiting after Android M was introduced on the Nexus 5X and Nexus 6P, with the Nexus family of devices following with updates soon after.

Now, official word from the U.S. HTC representative Mo Versi on Twitter has come, announcing the OTA roll out of Android M that's finally coming to the HTC One M8.

However, not all HTC One M8 devices are getting the rollout right now. Only those that are unlocked, and not tied to a particular wireless carrier -- with the system modifications and apps that comes along with.

"HTC One (M8) unlocked owners! Great news, all testing has been complete [sic] and the update for Marshmallow will be sent out within 24 hours. Thx" tweeted @moversi on Wednesday, Dec. 2, 2015.

That now puts HTC in the lead above its Android OEM rivals, as far as getting OTA rollouts of Android M out to the most kinds of devices so far. Previously the HTC One M8 Google Play Edition was also updated to Android 6.0 Marshmallow. The update includes the latest HTC Sense 7.0 UI layer on top of Android M, according to IBTimes.

HTC's Mo Versi also confirmed this week on Twitter that the HTC One M9, the company's current flagship, was slated for the update before the end of 2015 in the U.S., though the same "unlocked only" caveat almost certainly applies.

Meanwhile, HTC has slated the following devices to eventually get Android 6.0 Marshmallow: HTC One M9+, One E9+, One E9, One ME, One E8, One M8 Eye, Butterfly 3, Desire 820, Desire 826, and Desire 816. Conspicuously absent from that Android M update list is the company's first premium flagship, the HTC One M7.