The feature has been broken for weeks, and the fact that the option to activate it was completely missing from the Settings section made some users believe it was an intentional omission by Samsung. As it turns out, the reason was a plain old bug, or more precisely a conflict between the Google app and Samsung’s own voice command feature, S Voice.
A Google representative announced on the company’s product forums that the problem has been fixed. In order to get the feature to work, you will need to have the latest Google app update (4.5 or higher, the current one being 4.6). If you have the latest version and you can’t see the feature, try uninstalling the updates to the Google app and then updating it to the latest version. That’s how our Nirave managed to get it to work on his Galaxy S6 and S6 Edge. Worst case, you may need to clear the cached data of the Google app, though that means you will be signed out of your Google account.
One more thing: because of said conflict with S Voice, enabling “Okay, Google” from any screen will disable S Voice, except for the times when the screen is off. Basically, you will have to decide between the two assistants, but we’re pretty sure that won’t be a problem for many of you.