There was a brief period a couple of weeks back when Google Now on Tap feature got activated on devices running Android 6.0 preview. Now on Tap lets users pull up relevant information within any app, so you don’t have to leave what you’ve been doing to get more information. But that was short-lived since the feature wasn’t exactly ready for prime time so Google pulled the plug on it. But now that Android Marshmallow is as official as it can get, it would seem the feature is back on again. So those using the latest 6.0 preview might get a chance to use this feature.
Source: Droid Life