The Thai MFA clearly states regarding Extension of Stay of the DTV visa:
(through the Thai Immigration Bureau)
5 years Multiple Entries
180 days per entry
1-time for a period not exceeding 180 days per entry. After the maximum stay of 180 days + 180 days needs to depart the country and re-enter Thailand with
the same DTV visa within the visa validity date.
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fPdh6NtO/VISA_Information/New_Visa_Measures_July_2024.pdf