The role of espionage in the Soviet nuclear weapons program has been greatly exaggerated. While spies did accelerate their progress, it’s pretty clear that they could have developed nuclear weapons entirely on their own. I don’t think things would have been vastly different if the only information they had was that the US dropped a nuclear weapon on Hiroshima and Nagasaki.
The role of espionage in the Soviet nuclear weapons program has been greatly exaggerated. While spies did accelerate their progress, it’s pretty clear that they could have developed nuclear weapons entirely on their own. I don’t think things would have been vastly different if the only information they had was that the US dropped a nuclear weapon on Hiroshima and Nagasaki.