Negotiations between Iran and the United States over Tehran’s rapidly advancing nuclear program will move Wednesday to what’s known as the “expert level” — a sign analysts say shows that the talks are moving forward rapidly.

The United States and Iran are due to hold their second round of nuclear talks on Saturday, as what both sides are looking for in a deal begins to take shape.

That the talks are even happening represents a historic moment, given the decades of enmity between the two countries.