Do Thai immigration officials keep your passport during the waiting period for a non-O visa extension?

Thai immigration does not typically keep your passport during the waiting period for a non-O visa extension. Instead, you will receive a blue receipt and a date to return. However, there are exceptions; in some cases, certain offices may keep your passport overnight, especially if the decision-maker is not available. Overall, for most cases, you should expect to retain your passport while your extension is being processed.