If you read Dark Sun: The Making of the Hydrogen Bomb, the author claims that the information was mostly used by soviets to make sure they were on the right tr

If you read Dark Sun: The Making of the Hydrogen Bomb, the author claims that the information was mostly used by soviets to make sure they were on the right track, rather than outright copying. If there were 10 ways to do something, the soviets picked a couple of the most promising, then used intel to make sure they what they were doing was broadly similar to what the americans were doing. This still could save a lot of time and money vs. the american way of doing all 10 at once and seeing which worked.