After entering the US on a K-1 Visa, you and your Thai Fiancé must get married in the period of 90 days. In the event that the marriage does not occur inside the 90 days, the Visa holder will be required to leave the United States. Until the marriage happens, your Thai Fiancé is viewed as a temporary resident. A K-1 Visa holder cannot acquire an expansion of the 90-day time limit.
If the K-1 Visa holder intends to live and work permanently in the United States they should apply to become a permanent resident after the marriage. Please note, K-1 Visa holder will receive a “green card” and conditional permanent residence status for two years. Conditional permanent residency is granted when the marriage is less than two years old at the time the Adjustment of Status application is processed.
Note: A K-1 Visa holder can enter the United States only one time with this visa. Upon entry, the K-1 visa is cancelled, and an Electronic I-94 is issued upon entry and becomes the controlling document. If the K-1 entrant leaves the U.S. before marriage to the original petitioner, re-entry into the U.S. might not be allowed without a new visa. Also, if the K-1 entrant has applied for and is waiting on approval of an Adjustment of Status petition, the K-1 entrant should not leave the U.S. without also having applied for and received approved Advance Parole — doing so could result in the inability to re-enter the U.S., and it indicates abandonment of the petition for Adjustment of Status. (Note that even approved Advance Parole does not guarantee re-entry into the U.S.)