His result of 3:34.01 min is a new Lithuanian and world championship record, as well as the best result in the world this season.
Danas beat the Lithuanian record by 2.64 seconds and the world championship record by 0.31 seconds.
Having dominated from the very start, Ina Paipelienė's pupil beat Norwegian Henrik Christiansen by 2.63 seconds and Italian Gabriele Detti by 3.37 seconds.
This is D. Rapšys' first 400m award in a major competition, with his result being the third best of all time in the bracket.
All-time best men's 400m free style swimming results
1. Yannick Agnel (France), 3:32.25
2. Paul Biedermann (Germany), 3:32.77
3. Danas Rapšys (Lithuania), 3:34.01
4. Peter Bernek (Hungary), 3:34.32
5. Grant Hackett (Australia), 3:34.58