The Pentagon loves lying about troop levels in its major wars, and that's been particularly true in Iraq and Syria, where after being called out for underreporting several times they officially decided they were going to stop telling the public troop levels at all.
Maj. Gen. James Jarrard told reporters today that the US has about 4,000 ground troops in Syria, which is nearly 4,000 more troops than they've ever admitted to before. This figure apparently wasn't supposed to be public, as other Pentagon officials were quickly scrambling to walk back that announcement.
Pentagon spokesman Eric Pahon claimed to have no idea what the 4,000 figure was meant to represent, but insisted that the official figure for US troops in Syria is just 503. Whether that's a firm count, or just the usual Pentagon hand-waving number, was unclear.