QStash overhauled flow control to become a runtime-managed feature rather than a publish-time configuration. The rewrite addressed a core usability issue where cancelling rate-limited messages left slots blocked, making the feature practically unusable—now messages sit in an ordered wait list instead of being pre-scheduled to future slots, so cancellations free capacity immediately for new publishes. Alongside this, the team added pause/resume operations and an API to pin rate and parallelism values outside the publish path, plus expanded the flow control metrics endpoint to surface waitlist depth, active task counts, and effective limits so users can diagnose why messages queue. Two other threads emerged: sensitive data protection via field-level redaction in publish calls (body and header whitelisting), and regional expansion with US and EU endpoints to reduce latency.