We deployed the cancellations to our mainnet staging env relay-staging.flashbots.net.
The staging env is limited to sending and cancelling bundles, and it will only simulate bundles targeting currently built and the next blocks.
The bundles make it to our staging builder (0x81babe) and you should see the bundles landing on mainnet as you would be using the production endpoint.
Docs PR can be found here add cancellation docs by zeroXbrock · Pull Request #317 · flashbots/flashbots-docs · GitHub