Silly Con Valley reporting in ...
It's been pronounced "gif" since the late 80s.
"Gigawatts" is properly pronounced "jiggawatts", as the root of the word is the same as "gigantic". Likewise, the root of "GIF" is the same as "Graphic". Local colloquialisms may vary, of course, but they are not always pronounced the way the terminology was initially vocalized. Another case in point is the "rowter" vs. "rooter" pronunciation for "router". When we invented it, it was "rowter", but YMMV locally.
One wonders if the folks at Oxford will ever learn what NCSA Mosaic was (I can't be arsed to peruse my big dic to see if it's listed ...), and how Netscape built on that structure, including animated GIFs, in the early '90s. This is ancient tech, regardless, nothing to see here, pass along all ...
Ah, well. Beer, because beer has more meaning than this kind of pointless argument.