In the Hangouts app, how do I "mark all as read"? I'm using Hangouts for texting with my Samsung Galaxy S4. Usually the preview is enough to see the whole message. I hate having to open a message just to mark it a read. Is there a way to mark one, or several, or all messages as read without opening the message?
Unfortunate that this question had never received any love. Despite it being an entire year later, this functionality is not available as a feature in the Hangouts app on Android, iOS, or the web.

Here is the most relevant discussion from the Google Hangouts Product Forum


  Thank you for your feedback!
  Yes you are right, there isn't such a button yet. I think Hangouts wants to make sure that you really have read the messages without missing any information.
  However, I'll move your topic to the idea section for the team to consider it as a feature request.
  Nick Ross