The road is closed between Elphinstone and Crossgatehall. Apparently this is for patching, though closure of a two lane road implies more serious repairs. Apparently for 20 working days from yesterday.
I found it this morning on the way back from an early East Lothian excursion. My diversion meant a mile or so of cross country riding on 23 mm slicks. Fun!
Also if you are planning a trip into the Borders, the road between Bonchester Bridge and Newcastleton will be closed for around 10 weeks. See Scottish Borders Council.
This website is terrifying - there seem to be a lot of road closures for plenty of time in East Lothian. Perhaps these are exaggerated.