You may now have more messaging apps than you have close friends.

As of this week, there are six prominent chat apps in the United States — or as I see it, one too many. The latest to join the horde is Allo, Google’s highly anticipated messaging app that lets people take advantage of artificial intelligence to chat and make plans. Google began offering the smarter app on Wednesday.

Allo is appearing at a time when smartphones are already crowded with chat apps. IMessage from Apple is prominent among iPhone owners. Facebook Messenger is widely used on that social network. Also popular is WhatsApp, the chat service from Facebook that has largely replaced text messaging internationally. Add to the list Slack, a group chat tool that is popular among businesses, and Google Hangouts, which was released in 2013, and you have six.

I asked the British anthropologist Robin Dunbar, who studies the relationship between brain size and social circles, about the overload. His research has found that most people have the mental capacity to sustain 150 meaningful relationships, and among them, only five close ones.

“Having more apps than close friends doesn’t help, as something will have to go,” Mr. Dunbar said in an email, though he noted that the various messaging apps serve different purposes. Younger people are shying away from chatting on Facebook, for example, to have more private conversations on apps like WhatsApp.