Available on Studio and Enterprise plans. Instead of just before/after, you can upload a third audio file to compare three versions of a track — for example, raw, mixed, and mastered. Toggle labels are fully customizable (the defaults are "FIRST," "SECOND," and "THIRD").
Three-way comparisons always use the A/B/C selector. The single-button comparison control (see "Single-Button Comparison Control") requires exactly two versions, so it does not apply while a third version is present.