It’s included! And, in fact, we just launched the API publicly.

https://stripe.com/docs/disputes#early-fraud-warnings https://stripe.com/docs/api/radar/early_fraud_warnings

As for the percentage of false negatives, it really depends on your business. We definitely recommend looking at your own early fraud warning and disputes history to determine what makes the most sense for you.

It says on the page, the service costs 0.4% per transaction.

That's for the service in the original link. Not sure that's the same for the potential service under discussion here.