As I have mentioned multiple times over the last year or so, WMATA is in the process of completely overhauling the Metrobus system. By the middle of this summer, every single bus line will have a new name and most will have a new route.
I walked through all the changes that directly affect Georgetown in January. I definitely recommend you read that to get up to speed on the new routes.
Today I can give an update on the timing of the change. Right now WMATA is in the process of installing temporary signs for bus stops that will see a new route name. A couple examples are above. I’ve not seen any up in Georgetown yet, but I may have missed it.
More importantly, WMATA has announced that the day that the new system will become effective in June 29th. I had previously wondered if they were planning on phasing it in, but apparently not. Come midnight June 28th, the agency will snap its fingers and a completely new map will be in effect.
If you at all use Metrobus, you really need to start to get familiar with the new routes asap. In some cases, your reliable bus stop that you’ve been using for years will vanish (this is especially likely if you take the G2). So be prepared!
The Georgetown Metropolitan 
At the Washington Blvd Giant in Arlington, the 38B sign also says A58.
Didn’t notice it until today