from now on the total cost of the ticket will be the base amount for purposes of the 300-1 rule on issuing W-2G
here's the example from their email/website...
Changes to the United States tax code that go into effect Thursday will directly benefit TwinSpires.com players by letting you keep more of your winning and eliminating the need for most W2G forms.
TwinSpires reports winnings to the IRS when the return exceeds $600 and 300-to-1. TwinSpires automatically withholds from your winnings when the return exceeds $5,000 and 300-to-1.
Before Thursday, the 300-to-1 criteria was calculated using the base price of the wager; it is now calculated using the total cost of the bet.