You were arrested for DUI or Physical Control in King County in the last several months - but no DUI charges were filed. Are you off the hook? Probably not! This is a very common occurrence for State cases (State Patrol), especially in King County, Washington. (I recently had one filed 14 months after the arrest date.)
The King County Prosecutor has 2 years to file charges from the date of the incident on a DUI and/or Physical Control arrest. The typical time-line for filing has been 2-4 months from the date of arrest, but this is not set in stone.