Seems to some different answers to this one. On the Thai MFA site, definitely states 90 days
http://www.mfa.go.th/web/12.php
IV. List of countries which have concluded agreement on the
exemption of visa requirement for holders of ordinary
passport with Thailand and permitted to stay for 30 and
90 days
90 DAYS
1. Brazil 2. Republic of Korea 3. Chile
On the thaivisa.com site, its states
Chile : Republic of Chile 30 (Changed 2003-10-13)