If you run your tracker on Linux and an info hash whitelist approach would work for your use case, it might be worthwhile to have a look at aquatic_ws [0]. It relies on tungstenite [1] for websockets and achieves around 20x the throughput of the reference implementation when running with four threads.

I don’t know of anybody who runs it in production, but its sister implementation (BitTorrent over UDP) handles 80k responses per second with lower load averages than opentorrent.

[0] https://github.com/greatest-ape/aquatic

[1]: https://github.com/snapview/tungstenite-rs

(I am the developer of aquatic)