GM is dropping $100M to upgrade their Orion and Brownstown plants so they can start building the self-driving version of the Bolt EV. The plant is stated as being revamped to buil the Chevy Cruise AV as they already built one with the sensor technology on it to use as a Mule. So in addition to the Cruise AV, it would seem likely this is where the autonomous Bolt EV will be built as well, if it doesn't turn out to be one in the same.
https://media.gm.com/media/us/en/gm/home.detail.html/content/Pages/news/us/en/2018/mar/0315-orion.html
https://media.gm.com/media/us/en/gm/home.detail.html/content/Pages/news/us/en/2018/mar/0315-orion.html