The rapper made a concertlike entrance to the Forrest City low-security prison showing up late inside of a black conversion van with tinted windows.
T.I., whose real name is Clifford J. Harris Jr., was to report at noon, but the deadline passed as guards outside blocked reporters and onlookers from coming near the facility on a rural state highway.
It was not immediately clear if T.I.'s late arrival would affect his plea deal with prosecutors.
Federal prison spokeswoman Linda Thomas said the Atlanta rapper would be known inside by guards as federal prison inmate No. 59458019.
Traci Billingsley, another prison spokeswoman, said the prison had no special protections prepared for the rapper. The low-security prison has double-bunked cells and a large fenced exercise yard, where inmates in white jumpsuits could be seen Tuesday morning.
"We treat all our offenders in the same manner," Billingsley said.
T.I., 28, was arrested after trying to buy unregistered machine guns and silencers from undercover federal agents in 2007. That came after the rapper's best friend was killed following a party in Cincinnati in 2006. The rapper has said the bullets that killed his friend were meant for him.
The self-proclaimed "King of the South," T.I. had faced a maximum sentence of 10 years in prison and a $250,000 fine for each charge in his three-count indictment. However, he reached a plea deal with prosecutors after spending time on house arrest before his sentencing and speaking before community groups and high schools about the dangers of drugs, violence and guns.
Fans gathered down the road from the prison Tuesday and screamed "we love you, T.I!" when the black van pulled at the prison. Afterward, they shouted at TV cameras that "T.I. is the greatest!"
"We're still riding with the king!" yelled Porshe Tiswell, 22, of Forrest City.
Fan Eugene Smith, 24, of Forrest City defended T.I., saying the rapper feared for his life when he purchased the machine guns and silencers from federal agents.
"Somebody set him up, they snitched on him, so it's a whole different thing," Smith said. "We got to live a life, you know what I'm saying. We're out in the street life."
Upon his release, T.I. will be on probation for three years. He also must pay a $100,000 fine as part of his sentence.
His sixth album, "Paper Trail," has sold about 2 million copies and the rapper earned a Grammy for the song "Swagga Like Us" that he performed with Jay-Z. T.I. wrote the lyrics for the album while awaiting trial.
He performed Sunday in Atlanta and told the crowd he'd "see y'all in 366 days."
By Jon Gambrell