Vercel AI SDK 5.0: Technical Migration Reference

Critical Breaking Changes

Deprecated API Removal (BREAKING)

• Removed: All experimental_ prefixed functions (experimental_generateText, experimental_streamText)
• Impact: Code using experimental APIs will fail to compile
• Timeline: These were deprecated for months with warnings
• Migration Required: Replace with stable equivalents before upgrading

TypeScript Strictness Enforcement (BREAKING)

• Changed: Tighter TypeScript definitions across all APIs
• Impact: Previously compiling loose-typed code will fail compilation
• Affected Areas: Provider configurations, response handling, implicit any types
• Consequence: Better development experience but requires type annotation fixes

Legacy Stream Handler Removal (BREAKING)

• Removed: Old streaming interfaces and response formats
• Replacement: Consistent streaming patterns from AI SDK 4.x
• Critical: Error handling and completion behavior differs from legacy implementations

Configuration Requirements

Zod Schema Validation

• Dual Support: Both Zod 3 and Zod 4 supported simultaneously
• Recommendation: Zod 4 mini schemas for new projects
• Performance: Zod 4 provides smaller bundle size and better performance
• Edge Runtime: Zod 4 mini schemas critical for faster cold starts
• Migration Strategy: Gradual migration supported - don't upgrade everything at once

Provider Integration Impact

• All Providers Affected: OpenAI, Anthropic, Google Gemini configurations use updated APIs
• Bundle Optimization: Better tree-shaking - only bundle used provider integrations
• Multi-Provider Applications: Significant bundle size reductions possible

Resource Requirements

Migration Time Investment

• Phase 1: Enable strict TypeScript checking on current version (1-2 hours)
• Phase 2: Migrate experimental APIs to stable versions (varies by codebase size)
• Phase 3: Fix TypeScript compilation errors (budget significant time)
• Phase 4: Thorough streaming functionality testing (critical - behavior changed)
• Phase 5: Optional Zod 4 migration for new schemas only

Expertise Requirements

• Essential: TypeScript proficiency for fixing type annotation errors
• Important: Understanding of streaming API differences for error handling updates
• Recommended: Familiarity with Zod schema validation patterns

Performance Specifications

Bundle Size Improvements

• Reduction: Smaller overall bundle due to legacy code removal
• Tree-Shaking: Improved dead code elimination
• Edge Runtime: Notable cold start performance improvements
• Multi-Provider: Biggest bundle size wins for applications using multiple AI providers

Runtime Performance

• Edge Functions: Faster cold starts due to smaller bundles
• Cloudflare Workers: Improved performance in edge environments
• Production Impact: Better foundation for reliable AI applications

Critical Warnings

What Official Documentation Doesn't Tell You

Testing Requirements

• Critical: Streaming functionality must be tested thoroughly after migration
• Reason: New streaming APIs handle errors and completion differently than legacy
• Common Failure: Existing error handling code will likely need updates
• Testing Scope: All streaming endpoints, error conditions, and completion scenarios

Migration Gotchas

• Don't: Attempt simultaneous migration of SDK version + Zod version + TypeScript fixes
• Do: Staged migration approach to isolate issues
• Risk: "Upgrade everything at once" approach causes debugging nightmares

TypeScript Compilation Reality

• Expectation: Simple find-and-replace for experimental APIs
• Reality: Significant time investment fixing type annotations
• Hidden Cost: Code that "worked" with loose typing will require proper type definitions

Decision Criteria

Worth Upgrading If:

• Building production AI applications (stability and performance gains outweigh migration cost)
• Planning significant refactoring anyway
• Need better TypeScript development experience
• Deploying to edge runtime environments (bundle size matters)

Stay on AI SDK 4.x If:

• Prototype/experimental projects with rapid iteration needs
• Limited development resources for migration testing
• Stable application with no pressing need for new features
• Timeline Constraint: Plan migration within 6-12 months before support ends

Zod 4 Migration Decision

• New Projects: Use Zod 4 mini schemas (better performance, smaller bundles)
• Existing Projects: Zod 3 remains supported - no pressure to migrate
• Edge Deployments: Zod 4 mini schemas provide measurable cold start improvements

Implementation Failure Modes

Common Breaking Points

1. Experimental API Usage: Immediate compilation failure
2. Loose TypeScript: Compilation errors on upgrade
3. Legacy Streaming: Runtime errors due to changed error handling
4. Provider Configuration: Type errors in multi-provider setups

Recovery Strategies

• Pre-upgrade Testing: Run strict TypeScript checking before version upgrade
• Codebase Search: Find all "experimental_" usage before upgrading
• Streaming Validation: Test all streaming endpoints after migration
• Rollback Plan: Maintain ability to downgrade if critical issues discovered

Resource Links

• AI SDK 5.0 Documentation
• Migration Guide
• Provider Integration Docs
• Zod 4 Documentation
• Vercel Edge Functions Guide