About 3 months ago I went out on a tour of the section of the Anacostia Riverwalk Trail currently under construction from Benning Road to the Maryland boundary. Since then work has continued and more sections of the trail are paved.
Starting from the north, jeff sent these photos of the causeway and bridge near the New York Avenue bridge.
Bridge over a small stream just north of New York Avenue.
South of this, in the area of Kenilworth Gardens, I heard the trail is paved, but I haven't been out there to confirm that. But on the section between Nash Run and Benning Road there is more pavement.
"Traffic circle" north side of Watts Branch
Traffic diverter on the south side of Watts Branch Bridge (view previously seen in this photo)
Where the trail connects to Anacostia Avenue, it is at road width, which likely means it will be used by cars too. (same area)
Trail as road (same shot from August)
Where the road dead-ends - the old road continues through the park though
Where the trail connects to the road (same shot from August)
Trail over the hill (same shot from August)
Where the pavement begins, next to the old Pepco plant site (same shot from August)
Anyway, the whole trail is now paved from just north of Benning Road to Anacostia Avenue. There's still some work to be done on that stretch though, and bridges over Nash Run and the outflow stream as well as the causeway to tie it all together. But a fall 2016 opening, as projected on the project page, does seem within reach.
And though not part of this section, here's another piece of the Anacostia Riverwalk Trail under construction. This is the promenade at Florida Rock, right next to the baseball stadium (though for some reason it is all fudged up).