sfmuni.com has a text description of the 108-line
108: Stops Lane 3 daytime and evenings, outside after midnight
During the day, the 108 stops inside the Transbay Terminal approximately half-way along Lane 3, near the center stairways.
From midnight to 4:20 a.m., line 108 buses operate to and from the 5 Fulton stop on the ramp outside the Transbay Terminal, instead of using the top level inside.
Buses and F Line: Always ask for a transfer, even if you are not going to transfer to another line.