# Deprecation And Migration

> Plan deprecation and migration—replacement first, consumer migration, strangler and adapter patterns, zombie code removal. Use when sunsetting APIs, libraries, or legacy modules.

- Skill: `charlieviettq/deprecation-and-migration` (Agent Skill)
- Install (CLI): `npx skillmds@latest add charlieviettq/deprecation-and-migration`
- Raw SKILL.md: https://api.skillmd.com/api/skills/charlieviettq/deprecation-and-migration/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: charlieviettq (https://skillmd.com/u/charlieviettq)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/charlieviettq/deprecation-and-migration

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# Deprecation and migration

## Decision questions

1. Does the old system still provide unique value?
2. How many consumers? Migration cost each?
3. Is replacement production-proven?
4. Cost of NOT deprecating (security, maintenance)?

## Compulsory vs advisory

| Type | When |
|------|------|
| Advisory | Stable legacy, optional migration |
| Compulsory | Security risk, blocks progress — need tooling + deadline |

Default advisory unless risk justifies force.

## Process

1. **Build replacement** first
2. **Announce** — status, replacement, migration guide, timeline
3. **Migrate consumers** incrementally; owner migrates users when possible
4. **Remove** only after zero active usage verified

## Patterns

| Pattern | Use when |
|---------|----------|
| Strangler | Gradual traffic shift |
| Adapter | Old interface, new implementation |
| Feature flag | Per-consumer or cohort cutover |

## Zombie code signals

- No maintainer, active dependents, failing tests ignored, stale deps

## Output

Deprecation notice + migration steps + removal checklist.