An interesting decision by Dungeon World is that the game indicates that, upon reaching 10th level, a character is either retired, takes on an apprentice (which is played along with the old character), or starts over as a new class. In any case, the character stops gaining XP at 10th level.
This level cap is interesting. First, with the way it seems advancement might move in a game of Dungeon World, a character could hit this cap pretty quickly. You need 108 experience points to get to level 10. If you gain, conservatively, 3 per session from goals of defeating enemies, finding treasure, exploration, bonds, and alignment, and then you fail maybe 5 rolls per session, you’ll reach the level cap after 13-14 sessions.
This implies to me that Dungeon World is focused on telling tighter stories, and not quite as focused on a long term campaign OR that Dungeon World does not expect the players to be making 10-15 rolls per game session. Since some of the play samples have characters making a defy danger and hack and slack roll within the same couple of minutes of real time, it seems hard to imagine that a player won’t end up making 10-15 rolls in a 4 hour session (which the game explicitly assumes).
The 10 level cap can mean a few other things as well. Dungeon World assumes a fairly heroic starting character. After all, you’re unlikely to gain more than a couple points in traits which are used for your moves, and you’re unlikely to gain more than a couple of extra damage or armor. The game’s core mechanic always being a static 6-, 7-9, and 10+ mean that the math does NOT have very far to stretch. 10 levels then may then feel like an appropriate place for those abilities to stop in order to avoid outgrowing the game’s math where the targets never change.
Allowing a character to start over as a new class (although, you get to retain a few signature moves) is a strange inclusion to me. I suppose it is there because players are going to get attached and feel like their character’s story isn’t over, but for a game that focuses on the fiction being so important, having a character forget most of their old class moves and start over at level 1 seems like an awkward option. Having a second character join you, and staying at level 10 seems like a bit of a disruptive choice as well. Now you have a level 10 AND a level 1, while another player retired his character and started over with just a level 1 character. I get that insisting on character retirement is a bit heavy-handed, but the other options feel out of place.
The main take away from this is that, if there’s one flaw with the streamlined mechanic of dungeon world, it’s the inability of that mechanic to take much modification to the math. This limits the characters to fewer character levels, less magic item modifications, and no real way to model enemy strength into the roll (since rolls are player-attribute based only).