The K3 visa is intended especially for a US citizen who is sponsoring her foreign spouse for immigration purposes. The K3 Visa was created to shorten the long processing times forUS visas at the USCIS. The K3 visa is hence a "non-immigration" visa, this meaning that being in receipt of the K3 visa would not result in your wife becoming a permanent resident immediately once they arrive in the United States. The K3 however does allow your Thai wife to travel to the United States and live with you while she is waiting forher immigration status to be finanilsed. Your Thai wife may also bring her unmarried children who are under the age of 21 along using the related "K4 Visa" (note however, that ordinarily it will be necessary for you to file separate I-130 petitions for her minor children in order for them to become legal permanent residents).
The K3 Visa eligibility requirements are as follows:
1. You as the petitioner must be a US citizen, and the beneficiary must be your spouse;
2. There must be a pending immigration petition naming your wife as a beneficiary on file with the USCIS;
3. Your marriage must be valid, meaning that you have met all the requirements to have a valid marriage in the country/jurisdiction where you married, and were not subject to any impediment (such as a non-terminated prior marriage) to your ability to marry at that point in time.
Once your wife has obtained a K3 visa, she (and her unmarried minor children, using the "K4 visa") can travel to the United States and live with you for up to two (2) years. Presumably, during that time the USCIS will approve the K3 Visa petition filed by you, and you wife will be able to apply for an adjustment of status to become a legal permanent resident.
The K3 visa has never been a speedy process for a spousal immigration, however given the lengthy processing times at many of the USCIS service centers, it is a welcome alternative to your wife being forced to live outside the United States for an extended period of time, and the K3 Visa has already helped many families reunite.
Overview of the K3 Visa application process:
The K3 Visa process is complicated. The first stage is to file an immigration petition for your Thai wife. This would involve gathering a substantial amount of documents and information about both you and your Thai wife. Now although it is not really required for her children to receive a K4 visa, it is always best practice to proceed with filing immigration petitions for them. If the children are not your biological children, then it is necessary to view the facts of the marriage to ensure that you would be able to successfully sponsor your wife and her children for US immigration. In most cases this is possible however the rules are rather complicated.
The immigration petition can be filed with any one of the four USCIS regional service centers such as : the Vermont Service Center; the California Service Center; the Nebraska Service Center; or the Texas Service Center. You have to choose the immigration center where you reside.
After you receive an official USCIS receipt or equivalent proof that you had filed the immigration petition for your wife, you may then proceed to file a K3 visa petition with the USCIS' National Benefits Center ("NBC"). Unlike the other immigration petitions (which would be including K1 visa petitions), the National Benefits Center processes all K3 visa applications in the US, so your K3 visa petition will be processed there irrespective of where you live in the United States.
Once NBC has processed and approved your K3 visa petition, the K3 visa petition will be forwarded to the National Visa Center ("NVC"). The NVC will then in turn forward the documents to the US Embassy in Bangkok. Your spouse (and their/your minor children) would have to attend a visa interview at that US Embassy (technically, you do not have to attend the interview, but much better if your do). At this interview, the officer will usually focus on verifying the extent and nature of your relationship with your spouse and also your financial ability to support your wife and her/your children if they are admitted to the US. Other issues however might arise if your spouse has had any immigration issues in the US or if she has any kind of criminal history.
Once the K3 Visa has been granted to your spouse, they will be able to live with you in the US as the K3 Visa is a "multiple entry" visa. Your wife and children/child can travel using the K3 visa and can even obtain permission to work with their K3 visa. If possible however, once they arrive you should pursue an adjustment of status application as soon as possible based on their pending immigration petition This will help ensure that they become legal permanent residents (or at least have an application to become a legal permanent resident pending) before their K3 visa expires. It is possible (and would be probably best) to obtain permission for them to work and travel related to their adjustment of status application, instead of simply relying on their K3 visa status. Similar considerations apply for your wife/your minor children if they come to the U.S. on a K4 visa.
Benefits of K3 Visa
The K3 visas generally have shorter waiting periods compared to marriage-based immigration visa petitions
Your children can accompany you to the U.S. on the K-4
dependent visa as long as they are named in the visa petition