Fill a large pot or container with water and attach your sous vide machine inside. Set the water temperature to 130 degrees F for medium-rare doneness or pick a temperature based on your preferred level of doneness (e.g. 140°F for medium or 150°F for medium-well).
Brush the roast with olive oil and then sprinkle garlic powder, salt, and pepper evenly over it.
Place the seasoned tri-tip roast into a vacuum-seal bag, ziplock bag, or a sturdy zip-top plastic bag. Seal the bag using a vacuum sealer or the water displacement method.Make sure you remove as much air as possible. Also, make sure the bag is fully sealed above the waterline for safety. Cook the tri-tip at your chosen temperature for 4-6 hours. Cooking it longer will give you a more tender steak, but be careful not to cook it longer than the recommended time.
When the sous vide time is up, carefully remove the tri-tip roast from the sous vide bag and pat it dry with paper towels. The surface needs to be as dry as possible; Patting it dry helps create a better sear.
Heat an oven-safe skillet or cast iron skillet over high heat and then add about a tablespoon or two of oil to prevent sticking.
Once the pan is hot, give the tri-tip roast a good sear for 1-2 minutes per side, or until it gets a beautiful brown crust on it. You can use a hot grill, broiler, or searing station instead.
Loosely cover the seared tri-tip with aluminum foil and let it rest for about 5 minutes. This will help the juices redistribute and keep your meat moist.
Slice your sous vide tri-tip on a cutting board against the grain into thin slices and serve it immediately with chimichurri sauce.