Kitty does not use SIXEL, but defines it's own format: https://sw.kovidgoyal.net/kitty/graphics-protocol.html

KiTTY is useful for Windows users but are any significant amount of people using it on Linux? I would imagine that aside from people using the default terminal emulators that come with their distro or desktop environment like xterm, gnome-terminal and konsole, the most widely used terminal emulator on Linux would be urxvt.

Personally I use terminology which I am satisfied with. https://www.enlightenment.org/about-terminology.md

OP is talking about this Kitty (https://sw.kovidgoyal.net/kitty/), not this one http://www.9bis.net/kitty/.

Ah, I see. Thanks.

Yeah I've used it on OS X. It renders fast and is the most responsive terminal I've tried (alacritty, iTerm2, Terminal.app). Its font rendering isn't super optimal, and it's a little rough (no hotkeys for zooming, etc.), but it's really your only option if lag bothers you.

Nowadays I just use terminal in gvim. It solved like all of my problems. Should've known Vim would save me again haha.

Another of the most popular (and enduring) terminal emulators, xterm, can be built to support sixel.