Wavelength for 5 players is easiest to run as one cooperative team: one Psychic gives a clue, four people agree on a position, and the role rotates after the reveal. The rulebook copy we checked says cooperative mode works well with two to five players. If your group wants a contest between teams, a 2v3 split is a practical house format, but it gives the larger side more voices and should be treated as an adaptation.
Choose the format before dealing cards. For a first session, use co-op and play five rounds so each person gives one clue. For a louder competitive night, keep teams fixed for an equal number of turns, rotate clue givers within each side, and accept that the teams are different sizes. This page focuses on a five-person setup rather than repeating the complete Wavelength rules or the separate four-player guide.