I didn’t find time to update that site, but that’s because I’m working on getting the new one running 
. You actually have very good timing posting this as we just updated the production backend to make this testable the other day. I’ll list out a few caveats here to start with:
- This is very much in flux, changes are occurring frequently and at any point it’s very possible that we’ll break something in the links I’m sharing further down in this post. Consider this an ‘early preview’.
- Be careful when loading games – I’d personally suggest running this in a separate browser from normal (e.g. if you use chrome normally try edge, firefox), and if possible using a separate makecode account (e.g. if you use microsoft sign in normally try a google login) to make sure you do not harm your existing projects. The link is a beta link, so all the normal concerns there apply.
- Please let us know if you run into issues! It’s possible we already know it’s an issue, or that we push a bad build and are already fixing it, but even then it’s super helpful to get feedback.
- One more thing to not is that it’s no longer p2p like the hackathon version – it’s now
host <-> server <-> guest, so inviting 3-4 players shouldn’t be harmful to the hosts perf from sending out extra messages as the server handles relaying the screen.
Anyways, with that out of the way, home page is https://arcade.makecode.com/beta--multiplayer, and https://arcade.makecode.com/beta--multiplayer?host=_VvPX5u9bx7fx will spin start up a session for you with a terrible ‘four players move with controller’ “game” I made in about 2 minutes.
In addition, in https://arcade.makecode.com/beta, at the end of the share dialog I added a ‘host multiplayer session button’ – you can see that it is currently very ugly (red icon on far right) so the color and icon will change soon (I picked a color at random with the thought that I needed something that would force us to actually pick a good one prior to release) but it works:
(one more thing to note, there is some lag when you join / host a session while the game is compiling where you can’t click buttons – should just be 2-3 seconds. I’m planning on moving compilation over to a webworker like in the main app so this doesn’t happen but I’m finishing up some other features first )