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Changelog And Deprecation Policy

Learn Changelog And Deprecation Policy for free with explanations, exercises, and a quick test (for API Engineer).

Published: January 21, 2026 | Updated: January 21, 2026

Table of Contents

Why this matters

APIs evolve. Without a clear changelog and deprecation policy, changes break clients, damage trust, and slow adoption. As an API Engineer, you will plan safe change rollouts, announce timelines, and guide developers to upgrade with minimal friction.

  • Real tasks: announce a breaking change, schedule a sunset, add deprecation headers, update documentation, and write migration notes.
  • Outcomes: fewer incidents, predictable releases, and a developer-friendly API experience.

Who this is for

  • API engineers and backend developers who release or maintain public/internal APIs.
  • Technical writers and PMs defining API change policy and release notes.

Prerequisites

  • Basic understanding of REST or GraphQL.
  • Familiarity with semantic versioning (major.minor.patch).
  • Ability to read HTTP requests/responses.

Concept explained simply

A changelog is a human-friendly history of what changed and why. A deprecation policy defines how you announce and remove old behavior over time.

Mental model

Think of changes as a runway with lights:

  • Blue light: Announce deprecation (safe to use, but will change).
  • Yellow light: Sunset scheduled (countdown started, strong messaging).
  • Red light: Removal (old behavior is gone).

Your job is to turn the lights on early, clearly, and consistently.

Practical standards and timelines

1) Decide change type
  • Patch: backward compatible fixes.
  • Minor: backward compatible additions.
  • Major: breaking changes.
2) Announce deprecation
  • State what is deprecated, why, and the alternative.
  • Provide a migration snippet.
  • Include target removal date or version.
3) Support window
  • Run old and new behavior in parallel for a clear period (e.g., 90–180 days).
  • Add warnings in responses, dashboards, or logs.
4) Sunset
  • Send deprecation/sunset signals (e.g., HTTP headers).
  • Increase visibility: docs notices, changelog reminders.
5) Removal
  • Remove the old behavior on the date/version promised.
  • Publish a final changelog entry with outcomes and any fallback.
Useful HTTP signals (conventions)
  • Response header Deprecation: true when a feature is deprecated.
  • Response header Sunset: 2026-06-30 indicating the planned removal date.
  • Optional Warning header with a short migration hint.

These are widely used patterns; confirm with your platform and clients before rollout.

Worked examples

Example 1: Renaming a query parameter (non-breaking path)

Change: /users?sort=name becomes /users?sort=full_name with fallback support.

Plan:

  • Minor release 1.4.0: Add full_name and keep name working.
  • Deprecate name now; removal in 120 days.

Changelog entry:

1.4.0 - Added 'sort=full_name'. Deprecated 'sort=name'. Removal after 2026-06-30. Use 'sort=full_name'.

Runtime signals:

Deprecation: true
Sunset: 2026-06-30
Warning: 'sort=name' is deprecated; use 'sort=full_name'
Example 2: Removing a response field (breaking)

Change: remove user.age field; replace with user.birth_date.

Plan:

  • Minor 2.3.0: Add birth_date, mark age deprecated.
  • Major 3.0.0: Remove age.

Changelog entries:

2.3.0 - Added 'user.birth_date'. 'user.age' deprecated; removal in 3.0.0 (2026-09-01).
3.0.0 - Removed 'user.age'. Use 'user.birth_date'.
Example 3: GraphQL field deprecation

Change: field User.phone becomes User.phoneNumber.

Schema:

type User {
  phone: String @deprecated(reason: "Use phoneNumber")
  phoneNumber: String
}

Docs note: The phone field will be removed in version 2026-08 schema cut. Clients should migrate to phoneNumber.

How to write a great changelog entry

  • Title: short and action-oriented (Added, Changed, Deprecated, Removed, Fixed, Security).
  • What changed and why (one sentence).
  • Impact: breaking or not, who is affected.
  • Migration: code snippet or exact steps.
  • Timeline: deprecation date and removal date/version.
  • References inside your docs (no external links required here).
Changelog template (copy/paste)
Version: X.Y.Z (YYYY-MM-DD)
Category: Added | Changed | Deprecated | Removed | Fixed | Security
Summary: One line describing the change.
Details:
- Impact: breaking/non-breaking; affected endpoints/fields.
- Migration: steps or snippet.
- Timeline: deprecate now; removal on YYYY-MM-DD or in vN.
Runtime signals (optional): Deprecation: true; Sunset: YYYY-MM-DD; Warning: short hint.

Common mistakes and self-check

  • Mistake: Announcing too late. Fix: publish deprecation at least one full release ahead.
  • Mistake: No migration instructions. Fix: include before/after request/response examples.
  • Mistake: Silent removals. Fix: set and honor a public removal date/version.
  • Mistake: Inconsistent versions. Fix: use semantic versioning and stick to it.
  • Mistake: One-time notice only. Fix: repeat reminders in changelog and runtime signals.
Self-check
  • Can a new developer understand what to change in under 2 minutes?
  • Is there a clear removal date or version?
  • Is runtime behavior communicating the same message as docs?

Exercises

These mirror the tasks below (progress is saved for logged-in users only; everyone can complete them).

Exercise 1: Draft a deprecation notice

Scenario: You will replace query parameter sort=name with sort=full_name. Support window: 90 days. Create a concise changelog entry and the runtime headers.

  • Include version (minor), date, impact, migration, removal date.
  • Propose Deprecation, Sunset, and Warning headers.

Exercise 2: Plan a breaking removal across versions

Scenario: Field order.total (number) will be replaced by order.amount.cents (integer). Design the timeline across 2 releases and write the changelog lines.

  • Show when you add the new field, when you deprecate the old, and when you remove it.
  • Include a short migration note.
Exercise checklist
  • Clear migration steps are present.
  • Removal date or major version is specified.
  • Runtime signals align with docs.
  • Language is concise and unambiguous.

Practical projects

  • Create a sample API changelog for a fictional service across 6 releases, mixing Added/Deprecated/Removed categories.
  • Implement a middleware that adds Deprecation and Sunset headers for flagged routes and logs first-time usage per client.
  • Write an internal deprecation policy document (1 page): announcement rules, minimum support window, headers to use, and approval flow.

Learning path

  • Start here: Changelog and deprecation fundamentals.
  • Next: API versioning strategies (URI vs header vs media type).
  • Then: Observability for deprecations (usage tracking, dashboards, alerts).
  • Finally: Rollout automation (feature flags, canary, staged removals).

Next steps

  • Adopt the changelog template for your current project.
  • Identify one upcoming change and design a 90–180 day deprecation timeline.
  • Add runtime signals to at least one deprecated endpoint.
Mini challenge

In 5 sentences, explain your deprecation policy to a new partner developer. Include how you announce, the typical support window, and where to find migration steps.

Quick Test & progress

Take the quick test below to check your understanding. Available to everyone; only logged-in users have their progress saved.

Practice Exercises

2 exercises to complete

Instructions

You are replacing sort=name with sort=full_name. The old parameter will be supported for 90 days starting today (assume date: 2026-03-01). Write a changelog entry and the runtime headers.

  • Use a minor version bump.
  • Include impact, migration, and the exact removal date.
  • Propose Deprecation, Sunset, and Warning headers.
Expected Output
A concise changelog item with version/date, clear migration to sort=full_name, removal date 2026-05-30, and example Deprecation/Sunset/Warning headers.

Changelog And Deprecation Policy — Quick Test

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