Tumblr just updated in a big way that allows users to engage with each other in real-time and on a threaded, one-on-one basis.

It has launched an instant messaging feature across the Android, iOS, and web versions of its service. Unfortunately, it is a limited launch, with only 1,500 users getting access to the feature right away, and then anyone that those people happen to message will also get the new feature, creating a domino-like rollout. The company plans to open it up to everyone else in December.

If you're interested in using Tumblr for instant messaging, here's everything we know about the feature so far...

Tumblr: What is it?

Tumblr is a website and mobile app that lets you share text, photos, quotes, links, music, and videos with the world. It began in 2007 and was purchased by Yahoo in 2013 for approximately $1.1 billion.

Tumblr: How does Tumblr instant messaging work?

Tumblr's new instant messaging feature adds a layer of private, threaded conversations to the service. To access it, go to your dashboard and look for a little smiley balloon icon. If you’re using the app, be sure you’ve updated to the latest version first.

From there, click the smiley icon to begin sending a message to anyone. Your recipient will automagically get the new instant messaging feature, along with your private message. If you don't see the icon yet, you will within a few weeks.

Private and group blogs can’t use instant messaging at this time, but other blogs can, and of course you can change your blog’s settings on the web so that you only receive instant messages from Tumblrs that you follow.

Oh, and instant messages can't be anonymous.

Tumblr: Why is Tumblr IM not widely available at launch?

Tumblr said it decided to roll out its new instant messaging feature in order to work out the kinks.

Tumblr: Didn't Tumblr already have private messaging?

Sort of. It had an interblog messaging service called Fan Mail. Tumblr said that once you recieve its new instant messaging feature, you’ll notice that old Fan Mail conversations can "keep kicking, but you’ll need to use messaging for initiating outgoing gems".

Also, even though Fan Mail is being phased out, Tumblr said you’ll still be able to use "asks and submissions" like always.

Tumblr: Could Tumblr IM replace Facebook Messenger?

Probably not. Facebook Messenger had more than 700 million monthly active users as of last summer, whereas Tumblr, which supposedly hosts over 261 million blogs but does not report monthly active users, is thought to be nowhere near as popular. By launching an instant messaging feature, Tumblr is simply trying to cater to its existing users who have long requested such a feature.

In other words: if you're dedicated to Facebook and use it as your main source of communication between friends, then you probably won't ever find yourself using Tumblr as an alternative instant messenger.

Want to know more?

Check out Tumblr's announcement for more details.