This is taken from the London Embassy website, relating to Non-immigrant Visas (including Type O):
'Multiple Entries Visa will be valid for 1 year from the date of issue. You must enter Thailand within the validity of visa. However, the permitted length of stay is up to 1 year from the date of your arrival in Thailand. Please carefully note the immigration stamp in your passport to make sure that you do not overstay your visa.'
This seems to say that the multi-entry visa is stamped allowing a visit length of one year. I'm a little confused as previous remarks in the group have implied that the length of stay is only 90 days. Can anyone clarify this?
TLDR : Answer Summary
The confusion arises from the differences between various Non-Immigrant visa types. The Non-Immigrant O visa allows for a 90-day stay upon entry, while the Non-Immigrant O-A visa grants a one-year stay, and the O-X visa allows for a five-year stay. It's crucial to check the suffix of the visa type to understand the permitted length of stay.