Yes, green Thai chili peppers are hot. They are rated at about 30,000 on the Scoville heat scale, which measures how hot a pepper is.  The hottest pepper globally is the Habanero pepper, which is rated at about 350,000 on the Scoville heat scale.  So, the green Thai chili pepper is not as hot as the Habanero pepper, but it is still a pretty hot pepper.