There’s no included allowance for third-party models on Premium, Super, or Ultra (individual or Teams). The included pool covers Grok models.
Third-party models are billed at API list prices through top-ups, starting with the first request, and you can set spending caps.
If you stay on your current Ultra plan, your included third-party usage continues as it is today.
On how long the current plan lasts: it isn’t going away today, and there’s no timeline for moving remaining customers. If that changes, you’ll get advance notice first.