To go along with ABI087 being rolled out to unlocked devices, AT&T has now pushed their security update for BlackBerry KEYone owners. This release is noted as being build ABI975 and features the same October security updates offered on the unlocked variants.
AT&T has yet to post the full changelog to their site, so we can't say for sure if there are any AT&T specific changes involved here, but the update has gone live since this morning. If you never got alerts of it, go ahead and check for updates. You might have it waiting for you or have to hang tight for a bit longer as AT&T generally slows rolls them out.