回复：若父母在美同住半年以上，可否减税？（父母没绿卡）

New regulations were introduced so only residents of Mexico or Canada in such situation can be claimed as dependents.

Some people did it, but it doesn't mean it won't be issue if audited.

on the side note, depends on your income, if AMT kicks in, you won't get much at all from claiming additional dependents.