They issued a 2nd class of share, BRK.B, which is around $280/share right now and equates to 1/1500th of an BRK.A share. Berkshire A shares are convertible to B shares, but the converse isn’t possible.
Their stock transfer agent will give you B shares in exchange for an A share, which is not a taxable event. It’s a mechanism to encourage arbitrageurs to keep the prices of the share classes in lockstep.
https://www.berkshirehathaway.com/brkshareholderinfo/compab....