The Bolt will have one speed as with most (all?) production EV's. Conversions (Porsche's, Beetles, etc) usually utilize the existing trans, but 1st gear is useless and rarely are they actually shifted.
Tesla played with a 2-speed transmission when developing the Model S, but decided the extra weight and complexity were not worth it. We may see 2 speed transmissions (seamless?) in the future, but the current consensus seems to be that for all but the heaviest vehicles (think trucks, buses) the advantages of a single speed outweigh the benefits of multi-speed gearboxes.
Details on the Bolt motor/reduction gearing can be found here:http://insideevs.com/deep-dive-chevrolet-bolt-battery-pack-motor-and-more/
Edit: This applies to BEV's - PHEV's all utilize multi-speed transmissions and a cost effective approach is to replace the torque converter with the electric drive unit. Mercedes (and BMW?) does this on their Plug-ins.