This had been hinted at previously, but now it’s official:
The Department of Defense announced today an adjustment to the deployment of the 4th Brigade, 10th Mountain Division to Afghanistan. The entire brigade will not deploy as previously announced in December 2004; instead one battalion-sized task force consisting of an infantry battalion and attached fire-support, communications and logistics elements will deploy to assist transition of the coalition operations to the NATO International Security Assistance Force in southern Afghanistan in mid 2006. The non-deploying elements of the brigade will remain prepared to deploy within 15 days.
This move will lower the US troop level in Afghanistan from about 19,000 to about 16,500.