Jeff Koons’s metallic sculpture of a balloon-animal, “Rabbit,” sold for $91 million at Christie’s on Wednesday—setting a record for a living artist at auction.

The 1986 stainless steel creature bested the $90.3 million paid last fall for David Hockney’s 1972 painting, “Portrait of an Artist (Pool with Two Figures).” It also restored bragging rights to Mr. Koons, who previously held the record with a delivery truck-size version of a different animal sculpture, “Balloon Dog (Orange),” that sold for $58.4 million six years ago.

Bidding for the 3-foot-tall “Rabbit,” one in a series of four, started at $40 million, but a quartet of bidders chased after it, with dealer Bob Mnuchin winning it for $80 million, or $91 million with Christie’s fees. It was estimated to sell for between $50 million and $70 million.

Mr. Mnuchin, whose son is Treasury Secretary Steven Mnuchin, sat in a trench coat in the middle of the auction salesroom and at one point bid with two fingers aloft like rabbit ears. He was cradling a phone with his other hand and bid for a client.

The seller of the “Rabbit” was the family of the late media mogul S.I. Newhouse.