NASA and Starlink have already been using ion drives with 10x ISP of chemical rocket engines. Using such drives a 3 stage with existing nuclear reactors as energy source can get to 150-200 km/s.
While it haven't been built yet, nothing seems to prevent ion drive even with 100x ISP of chemical rocket. That means we can get 1000-2000 km/s (acceleration with existing reactors would take about 100 years) and get to the closest star in 1000 years.
While it haven't been built yet, nothing seems to prevent ion drive even with 100x ISP of chemical rocket. That means we can get 1000-2000 km/s (acceleration with existing reactors would take about 100 years) and get to the closest star in 1000 years.