A 99%+ bet is a Polymarket outcome trading at 99¢ or above: the event is all but settled, yet shares still pay $1.00 at resolution. The remaining spread is the yield.
This page collects every such market, sorted by annualized return, and stacks holding-rewards APY on top where the market qualifies. These trades are low-risk, not no-risk — "almost certain" occasionally resolves the other way.