9 × 9 is the size Hitori is best known for in print. Lines carry more duplicates, so the opening reads take longer, and mid-solve you'll lean on corner patterns and 2×2 double-pairs rather than pure scanning.
The connectivity rule graduates from tiebreaker to primary tool here: watching which white regions could get cut off often decides cells the number rules leave open.
For a shorter session, play today's daily puzzle; for the rules and techniques, see the how-to-play guide.