Flow "early version" (0.1.0) was released in 2014. Now there's a chance that they had another version used internally at least 3 years prior, but at this point

Flow "early version" (0.1.0) was released in 2014. Now there's a chance that they had another version used internally at least 3 years prior, but at this point we're just speculating. But IIRC nothing in React docs at the time mentioned how great JSX is with static types. It was all about render functions. For now I'm sticking to Occam's Razor and the idea that JSX was a hack to make render functions usable.