Yes it is.....I came used it this evening as no-one on LT seemed to have any idea whether the Overground was running. I came via Stratford on the DLR. At Lewisham, I waited less than 5 mins for the P4 which was running all the way to Brixton. This morning they were running as I caught one from HOP to Lewisham, having given up on both Southern and the Overgound. I really don't understand why, if Southern were running on lines south of New Cross Gate, the Overground was suspended.