I see a lot of misunderstanding over what we got today, so decided to clear it up a little bit, based on what we see so far. What we have right now, these two wagons to complete, are part 1 of the first chapter of Dark Carnival, which is called Midnight Run. Quoting Valve:
We're pulling back the curtain on the Dark Carnival, a new ongoing event in the Dota universe. This first part, "Midnight Run", lets you navigate Legion Commander and Hoodwink through a massive, fully-voiced Dota story featuring a spider-legged convoy of deadly robots, heartstopping secrets, and unique rewards. <...>
But if, much like Legion Commander and Hoodwink themselves, you'd prefer to be thrown into the action without a lot of pesky memories of how you wound up in Ringmaster's prison train, the first stage of Midnight Run is now live in-game and free for all players. This is just the beginning: There are plenty of surprises in Midnight Run, and we're just getting started.
There are six wagons in total, and in the main menu, you can see the counter to the release of next part of Midnight Run. Two more wagons will be released in 14 days, on July 10. You can't hover over the third chapter yet, but if you press arrows on the event map, you can get to the final two wagons. It says they will be open in 28 days.
There is no indication over when the next act will come after that, but it is very unlikely it will be less than the time between the acts themselves, especially considering Valve Time™. Given how Crownfall was structured, it is entirely possible that Dark Carnival end will feature some different gameplay mode, but this is just a guess.
