The only difference lies in the model number only. In fact, the Keurig K50 and K55 are the exact same brewers in terms of both appearance and functionality. The Keurig K50 model was released before the K55, and at one point Keurig decided to simply "rebrand" the brewer as the K55. Perhaps this was simply a marketing effort to make the brewer appear newer or more updated. Regardless, don't let the model number fool you - there are virtually no other differences between the K55 and K50 brewers.