Nope. Key-bindings are executed on key-down. It could be possible with a key-press or key-up method, or with a repeat parameter which tells whether the key combination is being held down.

https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent/repeat

from the manual

If @ is added at the beginning of the keysym, the command will be run on key release events, otherwise on key press events.

from the manual

If @ is added at the beginning of the keysym, the command will be run on key release events, otherwise on key press events.

Sorry, I forgot to mention that I had already tried that and it didn't produce any different result from the default (as far as I can tell).

If this is still an issue, could you share the snippet in question?

Prefixing @ should really do the trick, maybe there is a problem with the command you want to execute.

I am not sure @ is what I need, maybe I didn't explain the issue correctly.

I am using st as my main terminal emulator and whenever I want to open it I do super + Return, however if I keep the keysym pressed long enough, it will keep opening up new terminals. I am trying to avoid that behaviour.

No, you did explain it perfectly well. I tried it myself and came to the same result as you did.

super + @Return
    st

This would work if keeping a key pressed would result in multiple KeyPress events but only in a single, final KeyRelease event. Using xev -event keyboard I determined that this is not the case; instead, every KeyPress is accompanied by a KeyRelease.

Unfortunately, it doesn’t seem possible to make sxhkd react only to the final KeyRelease event.

My conclusion: No, you cannot accomplish what you want using sxhkd only.

You could maybe achieve something similar using chords, though.
Otherwise you would probably have to tinker with your keyboard settings or use a script involving a timer tuned to the typematic rate. But I doubt it would be worth the effort.

@smeikx There seems to be a way to detect autorepeating keys using the XCB equivalent of XkbSetDetectableAutoRepeat, see https://stackoverflow.com/a/41403168

You could then expose this in sxhkd by providing a modifier that executes a command only once per key{press,release}.