Stress-test an API deprecation before partners, customers, and support treat a soft sunset note as a finished migration plan.
API deprecations fail when timelines ignore real migration effort, when replacement endpoints are incomplete, when versioning rules conflict with SDKs still in the wild, and when enterprise contracts still promise the old behavior. A clean changelog entry is not evidence that the ecosystem can move without breakage and churn.
What to put on the table
One sentence for what is deprecated, who is in scope, the sunset date, the success metric after thirty days of dual-run, and the rollback trigger. Attach usage by customer, migration guides, SDK status, and the support macros you will use. If product, engineering, and sales disagree on who owns first response to a blocked partner, stop and reconcile first.
Name the decision you will make if the stress test finds nothing new, and the delay criteria if replacement coverage or customer notice is not ready.
Attack surfaces
- Migration truth: endpoints, auth, pagination, and error shapes the new path still mishandles.
- Customer shock: cohorts with the largest rewrite cost and the shortest notice.
- Support load: tickets and partner escalations under realistic spike load.
- Contract promises: SLAs, enterprise terms, or quotes the sunset cannot meet.
- SDK and docs lag: clients and samples that still teach the old path after announce.
Optional legal seat if terms change. Optional sales seat if deals in flight still assume the old API.
How to run it
Feed Pingpong the deprecation draft, usage data, and migration notes. Early passes steelman the change. Later passes attack from partner, support, engineering, and skeptic seats. End with a pass that turns surviving objections into a longer dual-run, clearer guides, or a hold. Delete invented "they will just upgrade" reviews and dual-counted simplicity wins.
When the deprecation removes a field or auth mode, force partner and engineering seats to map every client that still depends on it. Internal tools and partner middleware count. A sunset that looks clean in a spreadsheet while the SDK still exposes the old path will fail on the first real week.
Force a day-after narrative: what happens if a top partner misses the date, if error rates spike in one region, or if sales sold against the old docs. If those stories are stronger than your mitigation plan, fix the package before announce. Related: stress-test a product sunset, stress-test a migration plan, stress-test a feature flag rollout, pretend you are the CTO, and the war-game decisions hub. Process: how to run a Pingpong.