Vercel AI SDK - Stop rebuilding your entire app every time some AI provider changes their shit

I built a chat interface with GPT-4 once. Took three weeks. Then the client wanted Claude for "better reasoning." Different API, different streaming, different everything. Had to rewrite most of it.

That's the problem. Every AI provider has their own API format. OpenAI does it one way, Anthropic another, Google something else entirely. Want to switch? Rewrite your app.

The Vercel AI SDK handles this. One interface for 20+ providers. Switch from OpenAI to Claude by changing one line. No joke - I've done it.

What This Fixes

Rate limiting: Every provider does this differently. OpenAI throws 429 errors, Anthropic has quotas that make no sense, Google's free tier just stops working. The SDK's retry logic actually fucking works, unlike most attempts.

Streaming: SSE streaming actually works now. No more broken WebSocket nonsense or random disconnects that make you want to quit programming.

TypeScript: Most AI SDKs have terrible types. This one has proper end-to-end typing. Your IDE catches errors before deployment does.

The AI SDK Core handles server-side stuff, AI SDK UI gives you React/Vue/Svelte hooks. Use them together or separately.

Version 5 came out August 2024. Added agent workflows, tool calling that streams, and custom data types. Migration guide if you're on v4 - upgrade can break things badly. Don't upgrade to 5.0.0 specifically, it has a memory leak that'll crash your app after a few hours. 5.0.4+ is safe.

Compared to alternatives? It's actually pretty good.

Provider Switching

Switch from OpenAI to Claude to Gemini by changing one line:

// Switch providers by changing one line (actually works!)
const model = openai('gpt-4');           // Fast but expensive
const model = anthropic('claude-3-5-sonnet');  // Slower but thinks better
const model = google('gemini-pro');      // Cheap but weird edge cases

Gotcha: Providers have different context limits, token counting, and tool calling quirks. Test thoroughly when switching providers.

Streaming

SSE streaming in SDK v5 is more reliable. Handles partial JSON, tool calls mid-stream, error recovery.

Gotcha: Corporate proxies kill SSE streams faster than you can say 'why isn't this working?' Also, React hydration errors will drive you insane if you mess up server components.

When streaming breaks, check Network tab. Should see pending request with content-type: text/plain; charset=utf-8. If it completes immediately with 200, your proxy killed it. I wanted to throw my laptop out the window debugging this - lost a weekend to this bug before realizing it was our corporate firewall.

Tool Calling

Tool integration works well. TypeScript inference, streaming tool calls, decent error handling. Supports MCP servers too.

Performance depends on the provider. Anthropic tool calls take 3-5 seconds. Google's unreliable as hell. OpenAI's faster but your wallet will hate you.

Agent Workflows

Agentic loops with stopWhen and prepareStep hooks. Debugging agent decisions sucks though - like debugging someone else's mind. Observability helps but you'll still spend hours figuring out loops.

Agent costs are terrifying - I've seen $500 bills from runaway loops in production. Set spending limits or prepare for credit card alerts at 3am when your agent decides to recursively call itself 10,000 times.

UI Hooks

The useChat hook works across React, Vue, Svelte. Message persistence works, error states don't break, streaming feels smooth.

One weird thing: React Strict Mode causes duplicate messages in dev and it'll drive you nuts. Production's fine but you'll think you're going insane during development.

Bottom Line

You can switch AI providers without rewriting your app, which is fucking miraculous in this ecosystem. Streaming works, TypeScript's good, React hooks don't fight you.

Gotchas exist everywhere. Monitor budgets for agents or prepare for bankruptcy when they go haywire, corporate networks break streaming and Corporate IT won't tell you shit about why, provider quirks still matter and will bite you at the worst possible time. But for web apps needing provider flexibility, it's the best option right now - which says more about how broken everything else is than how perfect this is.