The T-MB is the closest club to a "driving" iron, but is only available down to a 2 iron whether it has a stock or custom shaft.

Justin Thomas had a custom T-MB 1-Iron stamped with UNO at The Open

Since a "1" is not listed as either an available Utility or MOTO, my guess would be that is was a "2" bent to a 1 iron loft.

I saw it on his tweet today with a picture. I spoke with my fitter today and he said that a one iron is a 16*. My earlier post recommended the T-MB bent to 15* or 16* and he confirmed that. Order it that way from the factory after being properly fitted. You want to ensure that you get the right shaft/head combination. I trust my fitter who has been at it for over 25 years and he is booked normally two out.

Can't recommend the MB-T highly enough, I struggled with my 3 version for first couple rounds, now it's my go to club if fairway is tight.

The Titleist T-MB 2 iron stock is a 17* and I cannot remember the loft on a 1 iron, but I would go talk to a fitter about this and I bet you can get dialed in and get this club set to a one iron. I think one irons are around a 15* or 16* degree. It is my understanding that these are awesome utility irons. Think this will meet you need with a little tweaking. But see a Titleist fitter not a brick and motor store.

If you check the lofts, you'll discover that the 2 iron of today is the same loft as the 1 iron of 15 years ago. The 3 iron is the 2 iron, etc. Manufacturers have been reducing the loft for several decades now. One of the reasons that most iron sets are now 4-AW or 5-AW rather than 3-PW. So, Titleist T-MB 2 iron performs the 1 iron function.

My Titleist 962 1-iron is 16*. Just bend a T-MB 2-iron one degree stronger.

JT may have had a prototype not available for sale and may not come to market. With the stronger lofts on irons in the last few years, a 2 iron T-MB may well be longer that Mr. Nicklaus' famous 1 iron that he shared with God. The 2 T-MB can also be adjusted 2 more degrees for the desired results.

as the other guys said, the T-MB is available down to the 2 iron.
But surely a fitter can bend the club to a 1 iron

Fellas, thanks for the great info and advice. Just goes to show how valuable this resource is and just generous TT members are. Thanks for your love of the game. I'll look into converting a 2 down to uno. I just turned 62; I've always heard us older gents aren't supposed to be able to swing these long sticks yet I love my T-MB 2 and 3. I'm longer and straighter than with fairway metals. In fact, my T-MB 3 replaces the AP2 3 in the bag for good now. I'd never threaten greens with the long ball at my age but with the T-MB I'm more accurate and score better now. Titleist keeps finding ways to make the game playable and fun for any age. I'm fan forever. Keep up the great work Titleist.