President Obama will make sweeping changes to U.S. immigration policy when he announces his plan Thursday night to unilaterally protect roughly 5 million undocumented immigrants from deportation.

The most far-reaching component of the president’s plan is to keep about 5 million people living in the U.S. illegally from being deported. An estimated 4 million of them would qualify for relief based on having children who are citizens or legal residents or because of the length of time they have been in the country, multiple sources familiar with the president’s plan confirmed.