According to a report from sources speaking to SamMobile, Samsung is planning to end support for Bixby Voice on versions of Android that are older than Pie. This change will come into effect on January 1, 2020, at which point the voice assistant will simply stop working.
There's a huge caveat here and a very easy fix. This only applies to Galaxy S9, S9+, S8, S8+, S8 Active, Note8, and A9 (2018) units that are still for some reason running Android 7.x Nougat or Android 8.x Oreo. So, only if you have any of these devices and you're still rocking Nougat or Oreo will Bixby's voice assistant features stop working for you, including Bixby Briefing, which gives you a summary of your upcoming day when your alarm goes off.
The easy fix is sort of obvious, and that is updating your handset to Android 9 Pie, which should already be available for all of these models. With that version of the OS you're also getting Bixby 2.0, with a new voice interaction UI and better natural language processing that leads to improved conversations, as well as quicker response times.