Clip (or stand) sous vide machine to a tall large pot. Fill the pot with warm water to height according to manufacturer’s instructions (keep in mind that steaks, when added, will cause water to rise).
Rub steak on all sides with garlic powder, onion powder, 1 tsp. salt, and ¼ tsp. pepper. Place steak in bag.
Lightly bruise rosemary and thyme by smacking them against a cutting board or lightly rolling in your hands (this will helps release the volatile oils). Add herbs to bag.
Vacuum seal or partially close resealable bag, getting as much air out as possible to keep bag from floating, and place in water bath. If using a resealable plastic bag, push down into water to submerge (this will push more air out of the bag) and fully close. To ensure proper cooking, contents of the bag need to be completely submerged in water. Turn on machine and heat water to 130°. This temperature will give you a tender, perfectly medium-rare steak (adjust 5° either way if you like your meat more or less well done).
Using a small clip, secure top edge of resealable bag to rim of pot, positioning it opposite the machine’s water outlet; as the water circulates, it will help keep the bag submerged. If using a vacuum-sealed bag, you may need to set a small plate on top to prevent floating. Cook steak, maintaining water bath at 130°, 2½ hours. Remove bag from water bath and let steak rest in bag 15 minutes (this lets the steak absorb some of the juices).
Remove steak from bag and pat dry with paper towels. Season all over with salt and pepper. Let air-dry a few minutes.
Heat a large cast-iron skillet over high until very hot. Add oil and cook all 4 sides of steak until a nice crust forms, 1–2 minutes total (it happens fast, so don’t walk away). The steak is already perfectly cooked; this step is to get some color and texture on the exterior. Slice steak against the grain, if desired, and season with salt and pepper. (The steak may appear slightly gray when you first cut into it but will turn bright pink when exposed to air.)