Masayoshi Son reduced the SoftBank Group shares he’s pledged to lenders by $2.1 billion in recent months, lowering his collateral after bets on artificial intelligence propelled the latest comeback in his volatile technology fortune.

Son trimmed his committed shares by 19.4 million to around 154.2 million, according to a filing earlier this month. About 31% of Son’s holdings in the Tokyo-listed company are now pledged to banks, down from near 39% in March 2020, data compiled by Bloomberg show.

The bulk of Son’s $35.3 billion fortune derives from a stake of just over a third in SoftBank, the Tokyo-listed conglomerate he founded that oversees a global empire of investments from chipmakers to startup ventures. SoftBank shares surged almost 200% to peak at the end of October on the back of an AI frenzy. Shares have given up some of the gains lately on fears of a bubble in the sector, but are still heading for the biggest yearly gain since 2013.