The other night I took the 52 bus from 14th and U, and the bus was one of those double-length, articulated buses -- the ones with the flexible elbow in the middle. I had never seen that before on 14th, only Georgia and H Street, but then yesterday I saw another articulated 52, so it must be a thing.
I can't find it on the WMATA website, but this is a good change -- the 14th Street buses are often quite crowded, so anything that can pack more people onto one bus is good in my book. Especially in the mornings, the 14th Street buses are mobbed and sometimes have to skip stops because they're full.
So far I've only seen these in the evening, not morning, so it's not clear to me if it's just an evening rush hour thing or not. In any case, it's a positive development.
UPDATE: A commenter says they saw two in-service articulated buses during the day going southbound, so it must be all day.