Tim Berners-Lee's source code for the World Wide Web is the latest non-fungible token (NFT) to go up for sale.
Sotheby's in New York is selling the program that paved the way for the internet we know today more than 30 years after its creation.
The sale started June 23 and ends on Wednesday. Bidding had reached $2.8 million on Friday.
The lot includes an animated version of Berners-Lee's nearly 10,000 lines of code and a letter from the British-born computer scientist himself.
"Ten years ago, we wouldn't have been able to do this," said Cassandra Hatton, vice-president at Sotheby's, referring to the recent boom in NFTs.
Hatton said this work is unique because of its importance for the creation of the World Wide Web.
"That changed every aspect of your life," Hatton said. "We don't even fully comprehend the impact that it has on our lives, and the impact that we will continue to have on our lives."
An NFT is a digital object such as a drawing, animation, piece of music, photo or video with a certificate of authenticity created by blockchain technology that underlies cryptocurrency. It cannot be forged or otherwise manipulated.
NFTs currently generate several hundred million dollars in transactions every month.
NFT exchanges take place in cryptocurrencies such as bitcoin on specialist sites but traditional auction houses are seeking to capitalize on the phenomenon.
The most expensive NFT ever was sold by Christie's in March for $69.3 million.