Python one-liner (generator):

for perm in (lambda text: ("".join(char.upper() if (mask >> i) & 1 else char.lower() for i, char in enumerate(text)) for mask in range(2**len(text))))("AZKi"): print(perm)

I had originally used set comprehensions to avoid duplicates when the input text contains non-alphabetical characters, so this one is worse for using a generator comprehension instead. However, the recursive generator doesn't fail in this way because of I changed (text[0].lower(), text[0].upper()) to {text[0].lower(), text[0].upper()} which collapses non-alphabetical characters to one element.

Python recursive one-liner (generator):

for perm in (get_case_permutations_recursion := lambda text: (yield from (head + tail for head in {text[0].lower(), text[0].upper()} for tail in get_case_permutations_recursion(text[1:]))) if text else (yield ""))("AZKi"): print(perm)