As of October 1st citizens from 53 countries that are able to enter Thailand visa exempt will get a stamp for 45 days (up from 30). Currently it’s due to revert back to 30 days on March 31st next year - although we may hear closer to that date if things have changed.
What hasn’t changed for these citizens is that they may apply for one extension of their entry for a further 30 days at a local immigration office. Extensions have NOT changed to 45 days.
[edit: It appears the official order did actually include the 6 countries with a bilateral 30 day entry, who would get a pp30 entry stamp. Deleted that paragraph as an earlier edict from the PR Department had said they weren’t. ]
All extensions of any duration cost 1,900 baht.
If you’re from one of the 53 countries then do the maths on whether you’re better off buying a tourist visa prior to entering Thailand (approx £30/$35) where you’ll be stamped in for 60 days or enter visa exempt for free but need an extension to cover the days you need for 1,900 baht (approx £45/$50). Max entry with an extension would be 75 days, or tourist visa 90 days.
Edit: Forgot to mention that visa on arrival (VOA) countries will get 30 days on arrival - up from 15.