Tesla added an additional assembly line at the Fremont plant.[1] This doubled production capacity. Cost about $100M. They already run two 9-hour shifts and six days a week.
[1] http://insideevs.com/teslas-2nd-production-line-capable-pump...
[1] http://insideevs.com/teslas-2nd-production-line-capable-pump...
Here's a long video of the assembly process in 2015.[1] This is useful, rather than the usual quick montage of cool robot scenes. There was a surprising amount of manual assembly in areas where other manufacturers are automated.