Whisk peanut butter, soy sauce, vinegar, oil, and garlic in a large bowl until combined. Whisk in 1/4 cup water (mixture should be pourable).
Bring a large pot of water to a boil over high. Add noodles; cook, stirring often, until al dente, about 6 minutes. Drain and rinse with cold water until cool; drain well.
Add noodles to peanut butter mixture, tossing gently to combine. Top with herbs, peanuts, and chili crisp, if using.
