Why Version Your API

APIs evolve over time. Versioning allows you to make changes without breaking existing integrations.

The Problem

Without versioning:

# Version 1: name is a string
GET /api/users/1
{ "name": "Alice Smith" }

# Update: name becomes an object
GET /api/users/1
{ "name": { "first": "Alice", "last": "Smith" } }

# Result: All existing clients break!

Types of Changes

Non-Breaking Changes (Safe)

• Adding new endpoints
• Adding new optional fields
• Adding new query parameters
• Expanding enum values

Breaking Changes (Need Versioning)

• Removing or renaming fields
• Changing field types
• Removing endpoints
• Changing authentication
• Changing required fields

Benefits of Versioning

1. Client Stability

Existing clients continue to work.

2. Gradual Migration

Clients can upgrade on their schedule.

3. A/B Testing

Test new API designs with subset of users.

4. Documentation Clarity

Clear which version is documented.

Exercise: Identify Breaking Changes

When to Create a New Version

Do Create New Version:

• Restructuring response format
• Changing field types
• Removing functionality
• Changing authentication scheme

Don't Create New Version:

• Adding new endpoints
• Adding optional fields
• Adding new filter parameters
• Bug fixes

Version Lifecycle

v1 (current) ──► v1 (stable) ──► v1 (deprecated) ──► v1 (retired)
                     │
                     ▼
                v2 (current) ──► v2 (stable)

Stages:

1. Current: Latest version, recommended
2. Stable: Supported, receiving security fixes
3. Deprecated: Still works, migration recommended
4. Retired: No longer available

Summary

Versioning is essential for:

• Maintaining backward compatibility
• Enabling API evolution
• Supporting multiple client versions
• Managing change gracefully

In the next lesson, we'll explore different versioning strategies.