I confirmed the party member limit with Yoshi-P.
The party member limits for the dungeons introduced in patch 1.18 is:
- The Thousand Maws of Toto-Rak: 4-man limit
- The Dzemael Darkhold: 8-man limit
This means that for the 4-man dungeon, you must be in a party of 4 and only 4. If you are in a party that has over or under 4 members, you will not be allowed in the dungeon. Same goes for the 8-man dungeon.
We have decided on those hard-coded party member limits for now due to balance and server load concerns as a starting point. We will then gather feedback and input from the players as they play through the content in patch 1.18 so that we can further experiment with the party member limit and try to incorporate more variation into the game.
YoshiP says, "The 8-man party dungeon, "Dzemael Darkhold", has a reeeaaallly good boss drop, so please try it out!"