ΔE 28.6, loose: different enough that you should pick on purpose. Imperial Purple is noticeably lighter, warmer than Anthraquinone Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 29). Imperial Purple is noticeably lighter, warmer than Anthraquinone Blue.
The same difference applies the other way round: Anthraquinone Blue is noticeably darker, cooler.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Anthraquinone Blue on the colour wheel See Imperial Purple on the colour wheel
All matches: Anthraquinone Blue equivalents · Imperial Purple equivalents