The first locomotives that were built from the start with the 2-10-4 wheel arrangement were the ten members of the class I-1 of the Texas and Pacific from 1925. The goal in the development was to create a ten-coupled freight locomotive with a larger firebox to provide greater power at higher speeds. Since the Santa Fe had just rebuilt the first locomotive with this wheel arrangement from a different one, this wheel arrangement was now called “Texas”.

They had oil burning and a grate with an area of 100 square feet or 9.29 m². The area of the firebox was increased with a combustion chamber and two thermic syphons. There was also a booster in the trailing bogie and an Elesco feed water heater.

The ten I-1s had a driver diameter of 63.5 inches (1,613 mm) and a boiler pressure of 250 psi (17.25 bars). Between 1927 and 1929, four batches of 15 each were built, designated I-1a to I-1d. They now had a driver diameter of only 63 inches and a boiler pressure of 255 psi. They were also 4,000 pounds heavier, or another 5,000 pounds on the I-1d.

Although their service life was already coming to an end in 1948, three were equipped with Timken roller bearings on all axles and designated Class I-2. By the early 1950s all but the 610 and 638 were scrapped. While the 638 was also scrapped two years later, the 610 was preserved. It pulled the American Freedom Train in the 1970s and has not been operational since 1982. Today she can be found in Palestine, Texas.