El Chisme

They did testing with the assistance of South Africa back when SA was still in full-swing apartheid

We know the history of the Israeli nuclear program, where the bombs are made, and what their delivery systems are. All the surrounding countries certainly act like Israel has nukes, so their intelligence agencies clearly think they do. There have been numerous high profile leaks and mistaken admissions.

Is it possible there's a decades-long conspiracy to fake having nuclear weapons? Sure, anything is possible. But Occam's Razor says we should just assume they have them.

As a nation, bluffing you have nuclear weapons would be an incredibly stupid thing to do. It means your rivals will seek them out to restore balance of power. Israel has been fighting for decades to keep other Middle Eastern nations from acquiring nukes. And those nations have tried to acquire them precisely because of Israel's nuclear arsenal. They're trying to level the playing field. What happens if you fake having nukes, your rivals respond by getting some of their own for real, and then it's revealed that you never had them?

Faking you have nuclear weapons is a profoundly stupid idea. The only time you want anyone thinking you have nukes is if you actually have them.

Israel has never confirmed or acknowledged it officially. But there are people who have come out who plausibly could know who have claimed it to exist. I think the earliest example was in the early 80s, but I cannot remember that person's name atm.

Nuclear weapons and Israel

Israel is widely believed to possess nuclear weapons. Estimates of Israel's stockpile range from 90 to 400 nuclear warheads,[2][5][6][7][8][9][19]

I dont want to just quote wikipedia and leave it there but I have never heard of any Nuclear Israel denialism beyond them being cheeky about it.

https://en.wikipedia.org/wiki/Samson_Option

https://en.m.wikipedia.org/wiki/Arnon_Milchan

Well, "they" are also the U.S. of A so they basically have nukes

She's actually antisemitic so maybe this helps