Create an API Deprecation Debt Ledger Before the Sunset Date Slips Again

An internal API has a sunset date, but nobody can name every consumer. Traffic remains after the deadline, exceptions have no owner, and the old service still requires on-call support. That is migration debt.

Use one ledger

consumer,monthly_calls,owner,migration_hours,exception_until,last_seen
billing-ui,120000,team-a,24,,2026-07-18
legacy-export,80,team-b,40,2026-08-15,2026-07-17
unknown,9300,,unknown,,2026-07-18

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Track three costs separately:

migration_cost = estimated_hours * loaded_hourly_rate
run_cost = infrastructure + on_call + security maintenance
delay_cost = run_cost_per_month + risk_reserve

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Illustrative numbers are not ROI evidence. Run downside, expected, and upside scenarios, especially for unknown traffic and estimates that exceed one sprint.

Gate Required owner Stop condition consumer inventory platform unknown traffic above threshold migration kit API team clean-room example fails exception business owner missing expiry or rationale shutdown incident owner rollback untested

Make exceptions expire automatically. An expired exception should page its owner or disable the waiver workflow—not silently become permanent. Keep read-only telemetry after migration long enough to detect late consumers, but define retention.

This ledger does not capture every organizational dependency or prove that shutdown is cheaper. It makes assumptions reviewable. Which is more expensive in your system: one month of old-API operation or one unknown high-value consumer outage?