Taxes--winning amount when tax paperwork starts?

[giantsrule]

In a cheap MTT (in Vegas) what is the threshold amount that, if you win at least that amount, you have to fill out tax related paperwork and the casino reports it to the IRS? I tried searching and didn't find a clear answer. One thread suggested $600 another seemed to say any amount. I'm also curious why it seems to be lower for poker tournaments than for a bet at the sportsbook which I thought was 5 or 10K. Thanks.