Traditional Theravada fits the definition of Sutrayana very well. Naturally, it has moved slightly in the direction of Vajrayana as it modernized.
However, I was shocked to discover that:
Theravada has included Vajrayana for as long as it has existed—and still does!
Not many Western Buddhists know this. It’s exciting because it means that there are more diverse resources for creating modern Buddhist Tantra than I realized.