According to this declaration the US President suggests that there will be some US military mission in Afghanistan after the end of August:
I want to be clear: The U.S. military mission in Afghanistan continues through the end of August. We remain — we retain personnel and capacities in the country, and we maintain some authority — excuse me, the same authority under which we’ve been operating for some time.
Fast-forward to mid-August and the Taliban have reached Kabul:
Taliban insurgents entered the Afghanistan capital Kabul on Sunday, an interior ministry official said, as the United States evacuated diplomats from its embassy by helicopter.
According to this article, Kabul is likely to fall way faster than expected:
U.S. officials reportedly now predict that Kabul will fall much sooner than expected. Previous assessments predicted that the Afghan capital would surrender to the Taliban in six to 12 months after the departure of American forces. Now officials reportedly assert that Kabul could fall within 90 days. Given the degree to which Afghan government forces have melted away, rather than fight the Taliban, 90 days may be an optimistic prediction — which may be why some officials feel that the city will surrender in as little as a month.
How can U.S. military mission in Afghanistan exists if Kabul is very likely to fall anytime soon?