Reportable Gambling Winnings
Report gambling winnings on Form W-2G if:
The winnings (not reduced by the wager) are $1,200 or more from a bingo game or slot machine,
The winnings (reduced by the wager) are $1,500 or more from a keno game,
The winnings (reduced by the wager or buy-in) are more than $5,000 from a poker tournament,
The winnings (except winnings from bingo, slot machines, keno, and poker tournaments) reduced, at the option of the payer, by the wager are:
$600 or more, and
At least 300 times the amount of the wager, or
The winnings are subject to federal income tax withholding (either regular gambling withholding or backup withholding).
...
Foreign Persons
Payments of gambling winnings to a nonresident alien individual or a foreign entity are not subject to reporting or withholding on Form W-2G. Generally, gambling winnings paid to a foreign person are subject to 30% withholding under sections 1441(a) and 1442(a) and are reportable on Form 1042, Annual Withholding Tax Return for U.S. Source Income of Foreign Persons, and Form 1042-S, Foreign Person's U.S. Source Income Subject to Withholding. Winnings of a nonresident alien from blackjack, baccarat, craps, roulette, big-6 wheel, or a live dog or horse race in the United States from legal wagers initiated outside the United States in a parimutuel pool are not subject to withholding or reporting. See Pub. 515, Withholding of Tax on Nonresident Aliens and Foreign Entities.