Bring a large pot of water to a boil for the pasta.
Meanwhile, heat EVOO over medium-high heat in large skillet with tight-fitting lid. Add sausage and brown and crumble. Add onions, garlic, chili pepper and thyme; partially cover and soften 5 minutes. Add vermouth, stock and clams; cover and cook until clams open. Discard any unopened clams.
Cook pasta to al dente. Reserve half a mug of starchy cooking water and drain.
Add butter and parsley to clams and season with salt and pepper. Add pasta to skillet and toss with starchy water to combine. Serve immediately.