Which program does NOT belong to the early stages of US human spaceflight?

The program that does not belong to the early stages of US human spaceflight is indeed Mir. Mir was a Soviet space station that operated from 1986 to 2001 and was not a part of the United States' human spaceflight programs.

In contrast, the Mercury, Apollo, and Gemini programs were all pivotal early initiatives in U.S. human spaceflight. Mercury was the first program to put humans into space, aiming to evaluate human capability in weightlessness and other challenges of space travel. The Gemini program followed, focusing on testing spacecraft systems and conducting rendezvous and docking operations, which were essential for future missions. Apollo was legendary for landing humans on the Moon and establishing the United States' presence in space exploration.

Thus, Mir stands apart as it was not a U.S. program but rather a significant Soviet project, making it the correct choice for this question.