Sous vide is insurance. You set your exact target temperature, drop the bag in the water, and the meat physically cannot overcook, even if dinner gets delayed by an hour. The trade-off is that a water bath can't build a crust on its own. That's where the finish sear comes in: a screaming-hot skillet or grill for 60 to 90 seconds per side to get the Maillard browning the bath can't deliver. This is a two-stage technique; both stages matter.
The Bath
Season the tri tip with your rub, vacuum seal it (or use the water displacement method with a zip-lock bag), and drop it into a water bath set to 132°F for medium-rare. Cook for 3 to 4 hours. You can go up to 6 hours without any negative effect. The texture gets slightly more tender with time, but it won't turn mushy like a braise.
Bath temperatures by doneness: 125°F for rare, 132°F for medium-rare, 140°F for medium. Don't try to compensate for carryover. Sous vide doesn't have any. The meat is at temp.
The Sear
Remove the tri tip from the bag and pat it completely dry with paper towels. This is critical. Any moisture on the surface will steam instead of sear. Get a cast iron skillet or grill grate as hot as possible. Sear for 60 to 90 seconds per side. You can add a knob of butter, crushed garlic, and fresh thyme to the skillet during the last 30 seconds and baste the tri tip for extra flavor.
A charcoal chimney with a grate on top is another excellent sear station: easier to get to 700°F+ than a stovetop. Whatever you use, the surface needs to be hot enough that the crust forms in under two minutes; longer and the interior climbs past medium-rare.
Rest and Serve
Sous vide tri tip needs less rest than traditionally cooked meat because the internal temperature is already uniform. Five minutes is enough. Slice and serve.
The Crust Trick
For an even deeper crust after sous vide, chill the seared tri tip in the freezer for 10 minutes before the sear. The colder surface lets you sear longer without overcooking the interior. A counterintuitive move that meaningfully improves the bark.