ΔE 15.2, loose: different enough that you should pick on purpose. Ink Sepia is noticeably lighter, more saturated than Inktense Black.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Ink Sepia is noticeably lighter, more saturated than Inktense Black.
The same difference applies the other way round: Inktense Black is noticeably darker, more muted.
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 Inktense Black on the colour wheel See Ink Sepia on the colour wheel
All matches: Inktense Black equivalents · Ink Sepia equivalents