Today is the day that Hangouts finally loses SMS support. We were warned by Google about it months ago when Hangouts started showing a warning that it would no longer support the feature. But, as of today, it's finally set to happen. For anyone who isn't on Project Fi or Google Voice — both of which will continue to support SMS in Hangouts — this is the end of an era.
Many people, myself included, made the final push into Hangouts over other services when SMS support was added. The integrated conversations made it much easier to keep short communications together in one place. So far there's no word on if SMS support will be coming to Allo. Now that Hangouts support for SMS is finally over, we aren't really left with a clear migration method. Anyone that might have made use of it will have to either deal with using two separate apps again or move over to a new service.
If you are looking for recommendations, Google's stock Android Messages isn't so bad. But, if you've been enjoying having SMS and chats merged, that isn't really a solution. Allo is always an option. But, that's the same issue from the other side, you'd still need to find a way to send SMS messages. There's always Facebook Messenger or Signal, which both provide a combined SMS and chat solution. Each has its disadvantages, though. The latter doesn't have quite the same feature set that Hangouts did, and the former is a Facebook product.
Either way, it's closing time. You might have just enough left to send one last SMS before the lights are shut off. If you still plan on using Hangouts for chats going forward, make sure you've updated to the latest version over at Google Play or APKMirror.