On Sleeper, you can always draft or trade over the roster limit!
If you have three open spots on your bench heading into your rookie draft, but you have 5 picks, don't worry. You can still draft 5 players, but you will just have to cut down to meet the roster limit before your roster is eligible.
Sleeper leagues do not require rosters to be under the league limit prior to a trade or a draft completing.
Team owners who are over the limit will see something like this at the top of their team page:
When a team is over the roster limit they CAN:
Move eligible players to IR and Taxi Squad
When a team is over the roster limit they CANNOT:
Add Free Agents
Edit their starting lineup
A team owner does not have to be at or under the roster limit in order to gain points toward a matchup. They will not be able to adjust the lineup, so it would be locked.
Why do we allow users to go over the limit?
We call this behavior "lazy enforcement." We saw trade activity triple with this change.
It's something not many platforms think about but makes a huge difference in league activity due to the flexibility afforded.