API contract evolution
Hand over the evidence required for deprecation
The next team needs to know who still uses the old contract, what those callers depend on and which conditions allow it to be retired.
In this article
Transfer the caller inventory
List supported clients and integrations with owners, operations used and expected activity cycles. Include unknown callers as unresolved entries rather than omitting them from the plan.
Link traffic evidence to the inventory. A last-seen timestamp helps, but it should be interpreted against a monthly or seasonal workflow where relevant.
Document the communication and migration commitments already made. The receiving team should not have to infer them from old issue comments.
Preserve both contract suites
Keep fixtures for request defaults, response meaning and error behaviour under each supported version. Include the cases that motivated the new contract and those protecting older callers.
Record compatibility adapters and any deliberate limitations. If the old representation cannot express a new domain state, explain the chosen mapping and its accepted consequence.
Retain a reproducible client example for important integrations. This makes future incidents easier to diagnose than a server-only specification.
Rehearse the retirement decision
Ask the receiving team to identify the remaining old-contract traffic and explain whether it is ready to retire. They should combine usage, owner confirmation and successful migrated workflows.
Test the post-retirement response in a controlled environment. Confirm old callers receive the documented behaviour rather than an accidental generic error or unrelated page.
Review rollback and data compatibility for records created during coexistence. A retirement plan should not rely on restoring code that can no longer interpret current data.
Assign continuing ownership
Name who updates the inventory, handles migration questions and approves exceptions to the retirement date. Keep exceptions scoped and time-bounded according to the organisation's policy.
Remove obsolete routes, credentials and documentation deliberately after the gate is met, preserving historical release evidence where required.
A useful handover turns deprecation from an aspirational date into an evidence-based decision. The next team can explain which users were supported, how they moved and why the old contract is no longer needed.
Primary sources
Google AIP-185: API versioningGoogle AIP-180: backwards compatibilityReferences checked 11 September 2026.