This made me pause for a moment, and then I had to do some reading, but I think you might be confused.
Zyklon B is a pellet-based delivery mechanism for hydrogen-cyanide (HCN) gas. Hydrogen-cyanide had been used as pesticide starting in the 1880s, was used by Germany during WWI, and was banned after the war. The Zyklon B delivery mechanism was invented in 1922 and was utilized by the Nazi regime in the pursuit of their “Final Solution”.
Sarin gas (C4H10FO2P) does not include cyanide, was invented in Germany in 1938 and was never used against Allied targets. NATO and the USSR stockpiled Sarin beginning in the 50s, and it wasn’t banned until 1997.