Yesterday VG247 reported that Eidos Montreal was creating a new 'AAA' game, with the letter 'T' being the only clue given as to the project's identity.
It seems now that the game in question is, in fact, Thief 4. Not Trombone Rider.
If you check the Facebook profile pic of Stephane D'Astous, the general manager at Eidos Montreal, you'll see that the letter 'T' Thief logo is displayed.
That's good enough for VG247! Maybe.