APIs change. External services release v2. Internal services deprecate old endpoints. Libraries update their interfaces. Each change ripples through your codebase, touching every file that calls the affected API.
Manual API migration is tedious and error-prone. Find every call site. Understand the old signature. Apply the new signature. Test that it still works. Multiply by dozens or hundreds of call sites, and you've burned a week on purely mechanical work.
AI agents excel at exactly this kind of transformation. They understand both the old and new API shapes, find all affected code, and apply changes consistently across your entire codebase.
Why API Migrations Stall
Most API migrations follow a familiar pattern of delay:
Stage 1: Awareness The team learns about an API change. Maybe a deprecation warning appears. Maybe the changelog mentions it. Someone says, "We should update that."
Stage 2: Deferral Other priorities take precedence. The old API still works. The migration goes on a backlog.
Stage 3: Accumulation More API changes pile up. Each one adds to the eventual migration scope. The longer you wait, the bigger the task becomes.
Stage 4: Crisis Something forces the issue - a security vulnerability, end-of-life deadline, or performance problem. Now you're doing emergency migration work under pressure.
Stage 5: Pain The rushed migration introduces bugs. Testing is incomplete. The team swears to handle migrations promptly next time. (They won't.)
Automation breaks this cycle by making migrations easy enough to do immediately.
Types of API Migrations
Different API changes require different migration strategies.
Parameter Changes
When function signatures change:
@devonair update all calls to getUserData() to include the new required 'options' parameter
@devonair migrate all API calls from positional to named parameters
The agent finds every call site and updates the arguments appropriately.
Endpoint URL Changes
When REST endpoints move:
@devonair update all API calls from /api/v1/* to /api/v2/* with appropriate path mappings
@devonair migrate all user endpoints from /users/* to /accounts/* per the new schema
Response Shape Changes
When the data structure changes:
@devonair update all code handling UserResponse to use the new nested profile object
@devonair migrate from paginated responses with 'items' array to 'data' array
Authentication Changes
When auth mechanisms update:
@devonair update all API calls to use bearer tokens instead of API keys
@devonair migrate from session-based auth to JWT-based auth in all API clients
Library API Changes
When third-party libraries update:
@devonair migrate all moment.js usage to dayjs with equivalent methods
@devonair update all axios calls to use the new interceptor API
Migration Strategies
The Full Cutover
Migrate everything at once:
@devonair migrate all uses of API v1 to API v2 across the entire codebase
Best for: Simple migrations, small codebases, comprehensive test coverage.
The Gradual Migration
Migrate component by component:
@devonair migrate /src/features/users to API v2
Then:
@devonair migrate /src/features/orders to API v2
Best for: Large codebases, complex migrations, incremental testing.
The Facade Pattern
Create an abstraction layer:
@devonair create an API facade that supports both v1 and v2 calls
Then:
@devonair migrate all direct API calls to use the facade
Finally:
@devonair update the facade to use v2 internally
Best for: High-risk migrations, gradual rollout, A/B testing.
The Adapter Pattern
Add compatibility layers:
@devonair create adapter functions that convert v1 response shapes to v2 shapes
@devonair wrap all v1 API calls with the adapter for forward compatibility
Then remove adapters once all consumers are updated.
Handling Breaking Changes
Breaking changes require special care.
Analyzing Impact
Before migrating, understand the scope:
@devonair analyze impact of the UserService API change and list all affected files
@devonair identify all code paths that depend on the deprecated getUser() method
Knowledge before action prevents surprises.
Mapping Old to New
Create explicit mappings for complex changes:
@devonair map old API method names to new equivalents:
- getUser -> fetchUser
- createUser -> registerUser
- updateUser -> modifyUser
@devonair apply the method mapping to all API calls in /src
Handling Removed Features
When functionality disappears:
@devonair identify all uses of the deprecated 'legacy' parameter and propose alternatives
@devonair remove all calls to the deprecated sync() method and document affected functionality
Rollback Preparation
Prepare for problems:
@devonair create a feature flag to switch between v1 and v2 API implementations
Easy rollback reduces risk.
External API Migrations
Third-party APIs present unique challenges.
SDK Updates
When official SDKs update:
@devonair update the Stripe SDK from v8 to v9 and migrate all API calls
@devonair migrate from AWS SDK v2 to v3 modular imports
OAuth Provider Changes
When authentication providers update:
@devonair migrate Auth0 integration from v2 API to v3 API
@devonair update Google OAuth implementation to latest API version
Payment API Changes
Payment APIs require careful migration:
@devonair update Stripe payment intents implementation to current API version
@devonair migrate PayPal integration from REST API to current SDK
Cloud Provider APIs
Cloud services evolve constantly:
@devonair migrate AWS Lambda handlers to the current runtime API
@devonair update Azure Blob Storage API calls to current SDK version
Internal API Migrations
Your own APIs change too.
Microservice Refactoring
When service boundaries shift:
@devonair update all calls to the monolithic UserService to use the new User and Auth microservices
@devonair migrate from the legacy order-service endpoints to the new fulfillment-service API
GraphQL Schema Evolution
When schemas change:
@devonair update all GraphQL queries to use the new field names
@devonair migrate deprecated GraphQL mutations to their replacements
REST to GraphQL Migration
Changing paradigms:
@devonair convert REST API calls in /src/api to GraphQL queries
@devonair create GraphQL queries equivalent to existing REST endpoints
Testing API Migrations
Migrations must be verified.
Integration Tests
@devonair run integration tests after API migration to verify behavior
@devonair update integration test mocks to match new API responses
Contract Testing
@devonair verify migrated code against API contract tests
@devonair update Pact contracts to reflect new API shapes
Response Validation
@devonair add runtime validation for new API response shapes
@devonair verify all migrated calls handle new error response formats
Staged Rollout
@devonair create a staged rollout plan for the API migration with canary testing
Test in production safely before full rollout.
Monitoring Migration Progress
Track the migration state:
Migration Status
@devonair report on API migration progress: percentage of calls updated, remaining v1 usage
Know where you stand.
Deprecation Tracking
@devonair identify all remaining uses of deprecated API methods
@devonair schedule weekly: report on deprecation warning count trends
Error Monitoring
@devonair after migration: monitor for new error patterns that might indicate migration issues
Catch problems early.
Common Migration Patterns
Request/Response Shape Changes
Old:
const user = await api.getUser(userId);
console.log(user.firstName);
New:
const user = await api.getUser(userId);
console.log(user.profile.firstName);
@devonair update all user.firstName references to user.profile.firstName
Promise to Async/Await
Old:
api.getUser(userId).then(user => { ... });
New:
const user = await api.getUser(userId);
@devonair convert promise chains to async/await syntax in API calls
Callback to Promise
Old:
api.getUser(userId, (err, user) => { ... });
New:
const user = await api.getUser(userId);
@devonair convert callback-based API calls to async/await
Query Parameter Changes
Old:
api.search({ query: 'test', limit: 10 });
New:
api.search({ q: 'test', pageSize: 10 });
@devonair update API query parameters: query->q, limit->pageSize
Automating Ongoing Migrations
Don't just migrate once - build sustainable practices.
Deprecation Warnings
@devonair when deprecated APIs are used in PRs: flag for review
@devonair on PR: check for newly deprecated API usage and suggest alternatives
Dependency Updates
@devonair schedule weekly: check for API updates in dependencies and report changes
@devonair when major dependency versions update: analyze API breaking changes
Documentation
@devonair document all API migrations with before/after examples
Help future developers understand what changed and why.
Getting Started
Start with a scoped migration:
@devonair list all deprecation warnings in /src related to API usage
Understand what needs to change.
Then migrate a single module:
@devonair migrate all API calls in /src/features/users to current versions
Verify tests pass. Review the changes.
Then expand:
@devonair migrate remaining deprecated API usage across /src
Set up monitoring:
@devonair on PR: flag any newly introduced deprecated API usage
API migrations that happen automatically are API migrations that actually happen. Stop deferring - start automating.
FAQ
What if the new API behaves differently?
The agent migrates syntax, but behavioral changes need human review. When response shapes or error handling differs significantly, the agent flags these for attention rather than making assumptions.
How do I handle APIs without documentation?
The agent analyzes existing usage patterns and the new API implementation to infer the correct migration. For complex cases, it asks for clarification rather than guessing.
What about database schema migrations alongside API changes?
Database migrations need separate handling, but can be coordinated:
@devonair analyze the API migration impact on database queries and suggest schema changes
Can I migrate to a completely different API?
Yes, for larger transformations:
@devonair replace all uses of library-x with library-y, mapping equivalent functionality
The agent creates the mapping and applies it consistently.