Gevo’s major product is isobutanol fermented from starches. To make an acceptable jet fuel additive they’d need to go through several oil-refining-like chemical manipulations.
I think their original business plan was to capitalize on the availability of idled ethanol plants to produce isobutanol instead, as an alternative oxygenate for mogas. It is difficult to see how this will be cost competitive with classic path to jet fuel - refining of petroleum distillate. The environmental benefit may be modest when the agricultural and chemical processing impacts are factored in.
Ironically, less expensive isobutanol might be an attractive additive to ASTM unleaded avgas in view of its RVP and water rejection properties.