Sam Bankman-Fried should spend between 40 and 50 years in prison after being convicted for stealing US$8 billion from customers of his now-bankrupt FTX cryptocurrency exchange, prosecutors said on Friday.

"His life in recent years has been one of unmatched greed and hubris; of ambition and rationalisation; and courting risk and gambling repeatedly with other people's money," federal prosecutors in Manhattan wrote. "And even now Bankman-Fried refuses to admit what he did was wrong."

A jury found Bankman-Fried, 32, guilty in November on seven counts of fraud and conspiracy.

Lawyers for the former billionaire told US District Judge Lewis Kaplan that a five-and-a-quarter to six-and-a-half-year prison term would be appropriate.

They said FTX clients would get most of their money back, and that Bankman-Fried did not set out to steal.

Kaplan is scheduled to sentence Bankman-Fried on March 28 in Manhattan federal court. Bankman-Fried plans to appeal against his conviction and sentence. (Reuters)