Liz Sly is the Beirut bureau chief for the Washington Post. She says the military has confirmed that this letter is authentic:
BREAKING: The US military sends a letter to the Iraqi military announcing the “onward movement” of US troops “in due deference to the sovereignty of Iraq & as requested by the Iraqi Parliament & the Iraqi PM”. It’s a withdrawal. pic.twitter.com/tQHSsHTtez
— Liz Sly (@LizSly) January 6, 2020