API Versioning and Backward Compatibility
Learn strategies for evolving APIs without breaking existing clients, including versioning schemes and compatibility rules.
API Versioning and Backward Compatibility is a free System Design Basics for Backend Developers lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the System Design Basics for Backend Developers learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Why APIs Must Evolve Carefully
Once an API has clients, you cannot freely change it. Renaming a field or removing an endpoint can break every consumer. Versioning lets you evolve the API while existing clients keep working.
Breaking vs Non-Breaking Changes
Know the difference:
- Non-breaking: adding a new optional field, adding a new endpoint
- Breaking: removing a field, renaming a field, changing a type, making an optional field required
Non-breaking changes can ship without a new version; breaking ones cannot.
URI Versioning
The most visible scheme puts the version in the path. It is simple and cache-friendly, and clients can clearly see which version they call.
GET /v1/users/42
GET /v2/users/42Header Versioning
Alternatively, clients request a version via a header. This keeps URIs clean and treats the version as part of content negotiation.
GET /users/42
Accept: application/vnd.myapp.v2+jsonQuery Parameter Versioning
A lighter approach uses a query parameter, e.g. ?version=2. It is easy to test in a browser but mixes versioning with regular parameters and can complicate caching.
GET /users/42?version=2Semantic Versioning
SemVer (MAJOR.MINOR.PATCH) communicates intent:
- MAJOR: breaking changes
- MINOR: new backward-compatible features
- PATCH: backward-compatible fixes
For public HTTP APIs, the MAJOR number usually maps to the URI version.
Additive Change Discipline
The cheapest versioning is not needing a new version. Follow the additive rule: only add, never remove or rename. Clients ignore unknown fields, so adding is safe.
{
"id": 42,
"name": "Ada",
"email": "ada@x.com"
}
// Later, safely add:
{
"id": 42,
"name": "Ada",
"email": "ada@x.com",
"created_at": "2026-01-01"
}Deprecation, Not Deletion
When you must retire something, deprecate first. Mark it in docs, send a Deprecation or Sunset header, and give clients a clear timeline before removal.
HTTP/1.1 200 OK
Deprecation: true
Sunset: Wed, 31 Dec 2026 23:59:59 GMT
Link: </v2/users>; rel="successor-version"Versioning gRPC and GraphQL
It is not just REST. In gRPC, never reuse or renumber protobuf field tags — that breaks the wire format. In GraphQL, the convention is no versions at all: add fields and use the @deprecated directive on old ones.
Supporting Multiple Versions
Running several versions at once has a cost. Strategies include translating old requests to the new internal model, or routing versions to different handlers. Limit how many versions you support and sunset old ones on schedule.
Designing for Change Up Front
Reduce future pain by designing for evolution: prefer objects over bare values so you can add fields, avoid leaking internal enums, and document a clear compatibility contract from day one.
Quick Check
Test your understanding of API versioning.
Recap
You learned how to evolve APIs safely:
- Distinguish breaking from non-breaking changes
- URI, header, and query parameter versioning schemes
- SemVer and the additive-change discipline
- Deprecate with Sunset headers before deleting
- gRPC tag stability and GraphQL's deprecation approach
Frequently asked questions
Is the “API Versioning and Backward Compatibility” lesson free?
Yes — the full text of “API Versioning and Backward Compatibility” is free to read here on the web, and the System Design Basics for Backend Developers course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the System Design Basics for Backend Developers course, upgrade to CoddyKit PRO.
What will I learn in “API Versioning and Backward Compatibility”?
Learn strategies for evolving APIs without breaking existing clients, including versioning schemes and compatibility rules. You practise System Design Basics for Backend Developers with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start System Design Basics for Backend Developers?
No prior experience is required. System Design Basics for Backend Developers on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “API Versioning and Backward Compatibility” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this System Design Basics for Backend Developers lesson?
Yes. Every System Design Basics for Backend Developers lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- RESTful API Design Principles
- GraphQL and gRPC
- Message Queues & Event-Driven
- API Versioning and Backward Compatibility