Expert puzzles use the same advanced toolkit as hard: multi-house 45 steps, two-cell and three-cell innies, digits locked inside non-unique cages, triples, and cage splits. The difference is density and score. An expert puzzle keeps requiring those steps instead of collapsing into singles after one breakthrough. That is a deliberate filter. A board that is impossible for twelve minutes and then trivial is a frustrating board, and it does not qualify.
There are no single-cell cages and no given digits. The cage layout is the sparsest of the four sets, which means more ambiguous sums and more borders crossed. Uniqueness is still checked twice, by two different solvers, and the logic solver has to finish the puzzle inside this toolkit. If it needs a guess, the puzzle is discarded before it ever receives a number.
Plan on thirty-five minutes or more. Use notes sparingly and structurally: mark a discovered outie sum as if it were printed, because you will need it again after the next elimination. The players who finish expert reliably are not faster at arithmetic. They are more willing to write down a sum they calculated and trust it later.
The hint remains a description. On expert it will sometimes point at a split or a hidden cage rather than a placement. That is the step. Filling the cell is available on the second press, and it is often the wrong press if you wanted the practice. The completion screen will point you at the technique you leaned on, which is usually the one to read before the next expert.
Expert is a small set on purpose while we watch finish rates. A puzzle people abandon in the first three minutes gets reviewed. A puzzle people finish by guessing gets removed. The number stays reserved either way, so a link you shared does not silently become a different board.
Related reading: how to play, the 45 rule, and the combination table.