There's a new version of Hangouts rolling out to devices today, and it's a big jump from 4.0 to 4.2. I know that you're wondering. Does it fix that thing that you personally hate about Hangouts? Nope, that thing (whatever it is) is unaffected. This update is laying the groundwork for Android 6.0.
As you probably know, Android 6.0 will have a new permission system that has apps request access to more sensitive things. For example, access to your contacts. We found a number of strings in the APK related to this.
<string name="contacts_permission_allow_text">Allow</string>
<string name="contacts_permission_banner_text">Make it easy to find your friends</string>
<string name="contacts_permission_message_text">Allow Hangouts to access your contacts</string>
<string name="contacts_permission_no_thanks_text">No, thanks</string>
<string name="contacts_rationale_explanation">To continue, give Hangouts access to your contacts.</string>
<string name="contacts_rationale_next">Next</string>
<string name="contacts_rationale_title">Find your friends</string>
<string name="hangout_mic_permission_required">Joining a call requires permission to use your microphone.</string>
<string name="hangout_permission_not_granted">Unlock your device and give Hangouts permission to use your microphone and camera.</string>
This won't have any impact on devices running pre-Marshmallow versions of Android. Maybe there are minor bug fixes lurking in there somewhere, but we don't see any evidence of that right now. If you go in for anecdotes, some people say this build feels faster. Either way, you can grab the update from APK Mirror.
Source: APK Mirror