Given the paragraph around Star Trek starships, which is the fastest.

Context: The warp drive of the Prometheus-class made the ships of this class faster than any other starship in the fleet at the time in the mid 2370s. The warp drive was capable of maintaining speeds exceeding warp 9.9. (VOY: "Message in a Bottle")

Answer: The fastest starship in the Star Trek universe is the USS Prometheus