There seem to be at least 17 variants of the Air Tractor, and I’m not at all sure which one this is.
According to Wikipedia:
Leland Snow began designing his first airplane, the S-1, in 1951. The 23-year-old Snow completed test flights with the S-1 in 1953. Snow’s S-1 flew dusting and spraying jobs in the Texas Rio Grande Valley and in Nicaragua until 1957. He followed-up the S-1 with the models S-2A and S-2B, which were built when Snow moved to production facilities in Olney, Texas in 1958.
In 1965, Leland Snow sold his company to Rockwell-Standard and was appointed a Vice President of the Aero Commander division. During this time, the Model S-2R was developed and named the Thrush. The first 100 Thrush aircraft were built at the Olney Division before the plant was closed and Thrush production moved to Georgia in 1970. More than 500 aircraft were produced under Snow Aeronautical Corporation and Rockwell-Standard in Olney.
Snow resigned from Rockwell and devoted the next two years designing the Air Tractor. Construction began in 1972 on the AT-300, which later became the AT-301. Air Tractor’s first turbine model, the AT-302, was introduced in 1977.
Sixteen years later, Air Tractor delivered its 1,100th airplane and soon began expanding the Olney plant for increased capacity. Today, Air Tractor produces a line of aircraft that includes 400, 500, 600, and 800-gallon capacity planes powered by Pratt & Whitney piston or turbine engines.