DRIVERS-3239 : Summary of necessary driver changes Implement the new backpressure retry logic detailed in https://github.com/mongodb/specifications/blob/client-backpressure/source/client-backpressure/client-backpressure.md . Add opt-in token bucket support with the new adaptiveRetries URI and client option listed in https://github.com/mongodb/specifications/blob/client-backpressure/source/uri-options/uri-options.md . Token buckets are excluded from the first rollout phase of client backpressure support, see ba14b6b , copied below for convenience: WARNING: Client backpressure support will be rolled out in two separate phases. The first phase consists of backoff and jitter only, without token bucket adaptive retries. Implementing drivers MUST NOT implement token buckets in the initial release. If token bucket support has already been merged, it MUST NOT be able to be turned on by users. Commits for syncing spec/prose tests (and/or refer to an existing language POC if needed) https://github.com/mongodb/specifications/commit/1125200e4a6161d87cb5090860597eb8e8e90bf1 Context for other referenced/linked tickets