The Fiancee (K-1) visa is a non-immigrant visa, includes many qualities of an immigrant visas, and allows Fiancees of U.S. citizens to enter the United States for the purpose of marriage. Although it is a non-immigrant visa, the visa interview is typically handled by the Immigrant Visa Unit of the Embassy.
The K-1 visa is evaluated by three U.S. government agencies: USCIS, NVC and Embassy. All visa application are currently submitted to the USCIS office in Dallas and then assigned to different Service Centers, typically in California, Vermont and Texas. After USCIS approves the case, the case file is forwarded to the NVC for background check on your Fiancee. Then the case file is forwarded to the Embassy for final processing.
Upon entry on a K-1 visa, the visa is valid for 90 days (marriage must occur within 90 days of entry). If you and your Fiancee decide
that you will not get married, your Fiancee leave the United States. Fiancees cannot adjust their status to any other category besides adjustment their
status based on marriage to their U.S. citizen petitioner.