AI Sdk Core

AI SDK Core

Backend AI with Vercel AI SDK v5 and v6.

Installation:

npm install ai @ai-sdk/openai @ai-sdk/anthropic @ai-sdk/google zod

AI SDK 6 (Stable - January 2026)

Status: Stable Latest: ai@6.0.26 (Jan 2026)

BREAKING: Output API Replaces generateObject/streamObject

⚠️ CRITICAL: generateObject() and streamObject() are DEPRECATED and will be removed in a future version. Use the new Output API instead.

Before (v5 - DEPRECATED):

// ❌ DEPRECATED - will be removed
import { generateObject } from 'ai';

const result = await generateObject({
  model: openai('gpt-5'),
  schema: z.object({ name: z.string(), age: z.number() }),
  prompt: 'Generate a person',
});

After (v6 - USE THIS):

// ✅ NEW OUTPUT API
import { generateText, Output } from 'ai';

const result = await generateText({
  model: openai('gpt-5'),
  output: Output.object({ schema: z.object({ name: z.string(), age: z.number() }) }),
  prompt: 'Generate a person',
});

// Access the typed object
console.log(result.object); // { name: "Alice", age: 30 }

Output Types

import { generateText, Output } from 'ai';

// Object with Zod schema
output: Output.object({ schema: myZodSchema })

// Array of typed objects
output: Output.array({ schema: personSchema })

// Enum/choice from options
output: Output.choice({ choices: ['positive', 'negative', 'neutral'] })

// Plain text (explicit)
output: Output.text()

// Unstructured JSON (no schema validation)
output: Output.json()

Streaming with Output API

import { streamText, Output } from 'ai';

const result = streamText({
  model: openai('gpt-5'),
  output: Output.object({ schema: personSchema }),
  prompt: 'Generate a person',
});

// Stream partial objects
for await (const partialObject of result.objectStream) {
  console.log(partialObject); // { name: "Ali..." } -> { name: "Alice", age: ... }
}

// Get final object
const finalObject = await result.object;

v6 New Features

1. Agent Abstraction Unified interface for building agents with ToolLoopAgent class:

• Full control over execution flow, tool loops, and state management
• Replaces manual tool calling orchestration

2. Tool Execution Approval (Human-in-the-Loop)

Use selective approval for better UX. Not every tool call needs approval.

tools: {
  payment: tool({
    // Dynamic approval based on input
    needsApproval: async ({ amount }) => amount > 1000,
    inputSchema: z.object({ amount: z.number() }),
    execute: async ({ amount }) => { /* process payment */ },
  }),

  readFile: tool({
    needsApproval: false, // Safe operations don't need approval
    inputSchema: z.object({ path: z.string() }),
    execute: async ({ path }) => fs.readFile(path),
  }),

  deleteFile: tool({
    needsApproval: true, // Destructive operations always need approval
    inputSchema: z.object({ path: z.string() }),
    execute: async ({ path }) => fs.unlink(path),
  }),
}

Best Practices:

• Use dynamic approval for operations where risk depends on parameters (e.g., payment amount)
• Always require approval for destructive operations (delete, modify, purchase)
• Don't require approval for safe read operations
• Add system instruction: "When a tool execution is not approved, do not retry it"
• Implement timeout for approval requests to prevent stuck states
• Store user preferences for repeat actions

Sources:

• Next.js Human-in-the-Loop Guide
• Cloudflare Agents Human-in-the-Loop
• Permit.io Best Practices

3. Reranking for RAG

import { rerank } from 'ai';

const result = await rerank({
  model: cohere.reranker('rerank-v3.5'),
  query: 'user question',
  documents: searchResults,
  topK: 5,
});

4. MCP Tools (Model Context Protocol)

⚠️ SECURITY WARNING: MCP tools have significant production risks. See security section below.

import { experimental_createMCPClient } from 'ai';

const mcpClient = await experimental_createMCPClient({
  transport: { type: 'stdio', command: 'npx', args: ['-y', '@modelcontextprotocol/server-filesystem'] },
});

const tools = await mcpClient.tools();

const result = await generateText({
  model: openai('gpt-5'),
  tools,
  prompt: 'List files in the current directory',
});

Known Issue: MCP tools may not execute in streaming mode (Vercel Community Discussion). Use generateText() instead of streamText() for MCP tools.

MCP Security Considerations

⚠️ CRITICAL: Dynamic MCP tools in production have security risks:

Risks:

• Tool definitions become part of your agent's prompt
• Can change unexpectedly without warning
• Compromised MCP server can inject malicious prompts
• New tools can escalate user privileges (e.g., adding delete to read-only server)

Solution - Use Static Tool Generation:

// ❌ RISKY: Dynamic tools change without your control
const mcpClient = await experimental_createMCPClient({ /* ... */ });
const tools = await mcpClient.tools(); // Can change anytime!

// ✅ SAFE: Generate static, versioned tool definitions
// Step 1: Install mcp-to-ai-sdk
npm install -g mcp-to-ai-sdk

// Step 2: Generate static tools (one-time, version controlled)
npx mcp-to-ai-sdk generate stdio 'npx -y @modelcontextprotocol/server-filesystem'

// Step 3: Import static tools
import { tools } from './generated-mcp-tools';

const result = await generateText({
  model: openai('gpt-5'),
  tools, // Static, reviewed, versioned
  prompt: 'Use tools',
});

Best Practice: Generate static tools, review them, commit to version control, and only update intentionally.

Source: Vercel Blog: MCP Security

5. Language Model Middleware

import { wrapLanguageModel, extractReasoningMiddleware } from 'ai';

const wrappedModel = wrapLanguageModel({
  model: anthropic('claude-sonnet-4-5-20250929'),
  middleware: extractReasoningMiddleware({ tagName: 'think' }),
});

// Reasoning extracted automatically from <think>...</think> tags

6. Telemetry (OpenTelemetry)

const result = await generateText({
  model: openai('gpt-5'),
  prompt: 'Hello',
  experimental_telemetry: {
    isEnabled: true,
    functionId: 'my-chat-function',
    metadata: { userId: '123' },
    recordInputs: true,
    recordOutputs: true,
  },
});

Official Docs: https://ai-sdk.dev/docs

Latest AI Models (2025-2026)

OpenAI

GPT-5.2 (Dec 2025):

• 400k context window, 128k output tokens
• Enhanced reasoning capabilities
• Available in API platform

GPT-5.1 (Nov 2025):

• Improved speed and efficiency over GPT-5
• "Warmer" and more intelligent responses

GPT-5 (Aug 2025):

• 45% less hallucination than GPT-4o
• State-of-the-art in math, coding, visual perception

o3 Reasoning Models (Dec 2025):

• o3, o3-pro, o3-mini - Advanced reasoning
• o4-mini - Fast reasoning

import { openai } from '@ai-sdk/openai';
const gpt52 = openai('gpt-5.2');
const gpt51 = openai('gpt-5.1');
const gpt5 = openai('gpt-5');
const o3 = openai('o3');
const o3mini = openai('o3-mini');

Anthropic

Claude 4 Family (May-Oct 2025):

• Opus 4 (May 22): Best for complex reasoning, $15/$75 per million tokens
• Sonnet 4 (May 22): Balanced performance, $3/$15 per million tokens
• Opus 4.1 (Aug 5): Enhanced agentic tasks, real-world coding
• Sonnet 4.5 (Sept 29): Most capable for coding, agents, computer use
• Haiku 4.5 (Oct 15): Small, fast, low-latency model

import { anthropic } from '@ai-sdk/anthropic';
const sonnet45 = anthropic('claude-sonnet-4-5-20250929');  // Latest
const opus41 = anthropic('claude-opus-4-1-20250805');
const haiku45 = anthropic('claude-haiku-4-5-20251015');

Google

Gemini 2.5 Family (Mar-Sept 2025):

• Pro (March 2025): Most intelligent, #1 on LMArena at launch
• Pro Deep Think (May 2025): Enhanced reasoning mode
• Flash (May 2025): Fast, cost-effective
• Flash-Lite (Sept 2025): Updated efficiency

import { google } from '@ai-sdk/google';
const pro = google('gemini-2.5-pro');
const flash = google('gemini-2.5-flash');
const lite = google('gemini-2.5-flash-lite');

Core Functions

Text Generation

generateText() - Text completion with tools streamText() - Real-time streaming

Structured Output (v6 Output API)

Output.object() - Typed objects with Zod schema (replaces generateObject) Output.array() - Typed arrays Output.choice() - Enum selection Output.json() - Unstructured JSON

See "AI SDK 6" section above for usage examples.

Multi-Modal Capabilities

Speech Synthesis (Text-to-Speech)

import { experimental_generateSpeech as generateSpeech } from 'ai';
import { openai } from '@ai-sdk/openai';

const result = await generateSpeech({
  model: openai.speech('tts-1-hd'),
  voice: 'alloy',
  text: 'Hello, how can I help you today?',
});

// result.audio is an ArrayBuffer containing the audio
const audioBuffer = result.audio;

Supported Providers:

• OpenAI: tts-1, tts-1-hd, gpt-4o-mini-tts
• ElevenLabs: eleven_multilingual_v2, eleven_turbo_v2
• LMNT, Hume

Transcription (Speech-to-Text)

import { experimental_transcribe as transcribe } from 'ai';
import { openai } from '@ai-sdk/openai';

const result = await transcribe({
  model: openai.transcription('whisper-1'),
  audio: audioFile, // File, Blob, ArrayBuffer, or URL
});

console.log(result.text); // Transcribed text
console.log(result.segments); // Timestamped segments

Supported Providers:

• OpenAI: whisper-1
• ElevenLabs, Deepgram, AssemblyAI, Groq, Rev.ai

Image Generation

import { generateImage } from 'ai';
import { openai } from '@ai-sdk/openai';

const result = await generateImage({
  model: openai.image('dall-e-3'),
  prompt: 'A futuristic city at sunset',
  size: '1024x1024',
  n: 1,
});

// result.images is an array of generated images
const imageUrl = result.images[0].url;
const imageBase64 = result.images[0].base64;

Supported Providers:

• OpenAI: dall-e-2, dall-e-3
• Google: imagen-3.0
• Fal AI, Black Forest Labs (Flux), Luma AI, Replicate

Embeddings

import { embed, embedMany, cosineSimilarity } from 'ai';
import { openai } from '@ai-sdk/openai';

// Single embedding
const result = await embed({
  model: openai.embedding('text-embedding-3-small'),
  value: 'Hello world',
});
console.log(result.embedding); // number[]

// Multiple embeddings (parallel processing)
const results = await embedMany({
  model: openai.embedding('text-embedding-3-small'),
  values: ['Hello', 'World', 'AI'],
  maxParallelCalls: 5, // Parallel processing
});

// Compare similarity
const similarity = cosineSimilarity(
  results.embeddings[0],
  results.embeddings[1]
);
console.log(`Similarity: ${similarity}`); // 0.0 to 1.0

Supported Providers:

• OpenAI: text-embedding-3-small, text-embedding-3-large
• Google: text-embedding-004
• Cohere, Voyage AI, Mistral, Amazon Bedrock

Multi-Modal Prompts (Files, Images, PDFs)

import { generateText } from 'ai';
import { google } from '@ai-sdk/google';

const result = await generateText({
  model: google('gemini-2.5-pro'),
  messages: [{
    role: 'user',
    content: [
      { type: 'text', text: 'Summarize this document' },
      { type: 'file', data: pdfBuffer, mimeType: 'application/pdf' },
    ],
  }],
});

// Or with images
const result = await generateText({
  model: openai('gpt-5'),
  messages: [{
    role: 'user',
    content: [
      { type: 'text', text: 'What is in this image?' },
      { type: 'image', image: imageBuffer },
    ],
  }],
});

See official docs for full API: https://ai-sdk.dev/docs/ai-sdk-core

v5 Stream Response Methods

When returning streaming responses from an API, use the correct method:

For chat widgets and UIs, always use toUIMessageStreamResponse():

const result = streamText({
  model: workersai('@cf/qwen/qwen3-30b-a3b-fp8'),
  messages,
  system: 'You are helpful.',
});

// ✅ For chat UIs - returns SSE with JSON events
return result.toUIMessageStreamResponse({
  headers: { 'Access-Control-Allow-Origin': '*' },
});

// ❌ For simple text - returns plain text chunks only
return result.toTextStreamResponse();

Note: toDataStreamResponse() does NOT exist in AI SDK v5 (common misconception).

workers-ai-provider Version Compatibility

IMPORTANT: workers-ai-provider@2.x requires AI SDK v5, NOT v4.

# ✅ Correct - AI SDK v5 with workers-ai-provider v2
npm install ai@^5.0.0 workers-ai-provider@^2.0.0 zod@^3.25.0

# ❌ Wrong - AI SDK v4 causes error
npm install ai@^4.0.0 workers-ai-provider@^2.0.0
# Error: "AI SDK 4 only supports models that implement specification version v1"

Zod Version: AI SDK v5 requires zod@^3.25.0 or later for zod/v3 and zod/v4 exports. Older versions (3.22.x) cause build errors: "Could not resolve zod/v4".

Cloudflare Workers Startup Fix

Problem: AI SDK v5 + Zod causes >270ms startup time (exceeds Workers 400ms limit).

Solution:

// ❌ BAD: Top-level imports cause startup overhead
import { createWorkersAI } from 'workers-ai-provider';
const workersai = createWorkersAI({ binding: env.AI });

// ✅ GOOD: Lazy initialization inside handler
app.post('/chat', async (c) => {
  const { createWorkersAI } = await import('workers-ai-provider');
  const workersai = createWorkersAI({ binding: c.env.AI });
  // ...
});

Additional:

• Minimize top-level Zod schemas
• Move complex schemas into route handlers
• Monitor startup time with Wrangler

v5 Tool Calling Changes

Breaking Changes:

• parameters → inputSchema (Zod schema)
• Tool properties: args → input, result → output
• ToolExecutionError removed (now tool-error content parts)
• maxSteps parameter removed → Use stopWhen(stepCountIs(n))

New in v5:

• Dynamic tools (add tools at runtime based on context)
• Agent class (multi-step execution with tools)

Critical v4→v5 Migration

AI SDK v5 introduced extensive breaking changes. If migrating from v4, follow this guide.

Breaking Changes Overview

1. Parameter Renames

   • maxTokens → maxOutputTokens
   • providerMetadata → providerOptions

2. Tool Definitions

   • parameters → inputSchema
   • Tool properties: args → input, result → output

3. Message Types

   • CoreMessage → ModelMessage
   • Message → UIMessage
   • convertToCoreMessages → convertToModelMessages

4. Tool Error Handling

   • ToolExecutionError class removed
   • Now tool-error content parts
   • Enables automated retry

5. Multi-Step Execution

   • maxSteps → stopWhen
   • Use stepCountIs() or hasToolCall()

6. Message Structure

   • Simple content string → parts array
   • Parts: text, file, reasoning, tool-call, tool-result

7. Streaming Architecture

   • Single chunk → start/delta/end lifecycle
   • Unique IDs for concurrent streams

8. Tool Streaming

   • Enabled by default
   • toolCallStreaming option removed

9. Package Reorganization

   • ai/rsc → @ai-sdk/rsc
   • ai/react → @ai-sdk/react
   • LangChainAdapter → @ai-sdk/langchain

Migration Examples

Before (v4):

import { generateText } from 'ai';

const result = await generateText({
  model: openai.chat('gpt-4-turbo'),
  maxTokens: 500,
  providerMetadata: { openai: { user: 'user-123' } },
  tools: {
    weather: {
      description: 'Get weather',
      parameters: z.object({ location: z.string() }),
      execute: async (args) => { /* args.location */ },
    },
  },
  maxSteps: 5,
});

After (v5):

import { generateText, tool, stopWhen, stepCountIs } from 'ai';

const result = await generateText({
  model: openai('gpt-4-turbo'),
  maxOutputTokens: 500,
  providerOptions: { openai: { user: 'user-123' } },
  tools: {
    weather: tool({
      description: 'Get weather',
      inputSchema: z.object({ location: z.string() }),
      execute: async ({ location }) => { /* input.location */ },
    }),
  },
  stopWhen: stepCountIs(5),
});

Migration Checklist

• Update all maxTokens to maxOutputTokens
• Update providerMetadata to providerOptions
• Convert tool parameters to inputSchema
• Update tool execute functions: args → input
• Replace maxSteps with stopWhen(stepCountIs(n))
• Update message types: CoreMessage → ModelMessage
• Remove ToolExecutionError handling
• Update package imports (ai/rsc → @ai-sdk/rsc)
• Test streaming behavior (architecture changed)
• Update TypeScript types

Automated Migration

AI SDK provides a migration tool:

npx ai migrate

This will update most breaking changes automatically. Review changes carefully.

Official Migration Guide: https://ai-sdk.dev/docs/migration-guides/migration-guide-5-0

Top 15 Errors & Solutions

1. AI_APICallError

Cause: API request failed (network, auth, rate limit).

Solution:

import { AI_APICallError } from 'ai';

try {
  const result = await generateText({
    model: openai('gpt-4-turbo'),
    prompt: 'Hello',
  });
} catch (error) {
  if (error instanceof AI_APICallError) {
    console.error('API call failed:', error.message);
    console.error('Status code:', error.statusCode);
    console.error('Response:', error.responseBody);

    // Check common causes
    if (error.statusCode === 401) {
      // Invalid API key
    } else if (error.statusCode === 429) {
      // Rate limit - implement backoff
    } else if (error.statusCode >= 500) {
      // Provider issue - retry
    }
  }
}

Prevention:

• Validate API keys at startup
• Implement retry logic with exponential backoff
• Monitor rate limits
• Handle network errors gracefully

2. AI_NoObjectGeneratedError

Cause: Model didn't generate valid object matching schema.

Solution:

import { AI_NoObjectGeneratedError } from 'ai';

try {
  const result = await generateObject({
    model: openai('gpt-4-turbo'),
    schema: z.object({ /* complex schema */ }),
    prompt: 'Generate data',
  });
} catch (error) {
  if (error instanceof AI_NoObjectGeneratedError) {
    console.error('No valid object generated');

    // Solutions:
    // 1. Simplify schema
    // 2. Add more context to prompt
    // 3. Provide examples in prompt
    // 4. Try different model (gpt-5 or claude-sonnet-4-5 for complex objects)
  }
}

Prevention:

• Start with simple schemas, add complexity incrementally
• Include examples in prompt: "Generate a person like: { name: 'Alice', age: 30 }"
• Use GPT-4 for complex structured output
• Test schemas with sample data first

3. Worker Startup Limit (270ms+)

Cause: AI SDK v5 + Zod initialization overhead in Cloudflare Workers exceeds startup limits.

Solution:

// BAD: Top-level imports cause startup overhead
import { createWorkersAI } from 'workers-ai-provider';
import { complexSchema } from './schemas';

const workersai = createWorkersAI({ binding: env.AI });

// GOOD: Lazy initialization inside handler
export default {
  async fetch(request, env) {
    const { createWorkersAI } = await import('workers-ai-provider');
    const workersai = createWorkersAI({ binding: env.AI });

    // Use workersai here
  }
}

Prevention:

• Move AI SDK imports inside route handlers
• Minimize top-level Zod schemas
• Monitor Worker startup time (must be <400ms)
• Use Wrangler's startup time reporting

GitHub Issue: Search for "Workers startup limit" in Vercel AI SDK issues

4. streamText Fails Silently

Cause: Stream errors can be swallowed by createDataStreamResponse.

Status: ✅ RESOLVED - Fixed in ai@4.1.22 (February 2025)

Solution (Recommended):

// Use the onError callback (added in v4.1.22)
const stream = streamText({
  model: openai('gpt-4-turbo'),
  prompt: 'Hello',
  onError({ error }) {
    console.error('Stream error:', error);
    // Custom error logging and handling
  },
});

// Stream safely
for await (const chunk of stream.textStream) {
  process.stdout.write(chunk);
}

Alternative (Manual try-catch):

// Fallback if not using onError callback
try {
  const stream = streamText({
    model: openai('gpt-4-turbo'),
    prompt: 'Hello',
  });

  for await (const chunk of stream.textStream) {
    process.stdout.write(chunk);
  }
} catch (error) {
  console.error('Stream error:', error);
}

Prevention:

• Use onError callback for proper error capture (recommended)
• Implement server-side error monitoring
• Test stream error handling explicitly
• Always log on server side in production

GitHub Issue: #4726 (RESOLVED)

5. AI_LoadAPIKeyError

Cause: Missing or invalid API key.

Solution:

import { AI_LoadAPIKeyError } from 'ai';

try {
  const result = await generateText({
    model: openai('gpt-4-turbo'),
    prompt: 'Hello',
  });
} catch (error) {
  if (error instanceof AI_LoadAPIKeyError) {
    console.error('API key error:', error.message);

    // Check:
    // 1. .env file exists and loaded
    // 2. Correct env variable name (OPENAI_API_KEY)
    // 3. Key format is valid (starts with sk-)
  }
}

Prevention:

• Validate API keys at application startup
• Use environment variable validation (e.g., zod)
• Provide clear error messages in development
• Document required environment variables

6. AI_InvalidArgumentError

Cause: Invalid parameters passed to function.

Solution:

import { AI_InvalidArgumentError } from 'ai';

try {
  const result = await generateText({
    model: openai('gpt-4-turbo'),
    maxOutputTokens: -1,  // Invalid!
    prompt: 'Hello',
  });
} catch (error) {
  if (error instanceof AI_InvalidArgumentError) {
    console.error('Invalid argument:', error.message);
    // Check parameter types and values
  }
}

Prevention:

• Use TypeScript for type checking
• Validate inputs before calling AI SDK functions
• Read function signatures carefully
• Check official docs for parameter constraints

7. AI_NoContentGeneratedError

Cause: Model generated no content (safety filters, etc.).

Solution:

import { AI_NoContentGeneratedError } from 'ai';

try {
  const result = await generateText({
    model: openai('gpt-4-turbo'),
    prompt: 'Some prompt',
  });
} catch (error) {
  if (error instanceof AI_NoContentGeneratedError) {
    console.error('No content generated');

    // Possible causes:
    // 1. Safety filters blocked output
    // 2. Prompt triggered content policy
    // 3. Model configuration issue

    // Handle gracefully:
    return { text: 'Unable to generate response. Please try different input.' };
  }
}

Prevention:

• Sanitize user inputs
• Avoid prompts that may trigger safety filters
• Have fallback messaging
• Log occurrences for analysis

8. AI_TypeValidationError

Cause: Zod schema validation failed on generated output.

Solution:

import { AI_TypeValidationError } from 'ai';

try {
  const result = await generateObject({
    model: openai('gpt-4-turbo'),
    schema: z.object({
      age: z.number().min(0).max(120),  // Strict validation
    }),
    prompt: 'Generate person',
  });
} catch (error) {
  if (error instanceof AI_TypeValidationError) {
    console.error('Validation failed:', error.message);

    // Solutions:
    // 1. Relax schema constraints
    // 2. Add more guidance in prompt
    // 3. Use .optional() for unreliable fields
  }
}

Prevention:

• Start with lenient schemas, tighten gradually
• Use .optional() for fields that may not always be present
• Add validation hints in field descriptions
• Test with various prompts

9. AI_RetryError

Cause: All retry attempts failed.

Solution:

import { AI_RetryError } from 'ai';

try {
  const result = await generateText({
    model: openai('gpt-4-turbo'),
    prompt: 'Hello',
    maxRetries: 3,  // Default is 2
  });
} catch (error) {
  if (error instanceof AI_RetryError) {
    console.error('All retries failed');
    console.error('Last error:', error.lastError);

    // Check root cause:
    // - Persistent network issue
    // - Provider outage
    // - Invalid configuration
  }
}

Prevention:

• Investigate root cause of failures
• Adjust retry configuration if needed
• Implement circuit breaker pattern for provider outages
• Have fallback providers

10. Rate Limiting Errors

Cause: Exceeded provider rate limits (RPM/TPM).

Solution:

// Implement exponential backoff
async function generateWithBackoff(prompt: string, retries = 3) {
  for (let i = 0; i < retries; i++) {
    try {
      return await generateText({
        model: openai('gpt-4-turbo'),
        prompt,
      });
    } catch (error) {
      if (error instanceof AI_APICallError && error.statusCode === 429) {
        const delay = Math.pow(2, i) * 1000;  // Exponential backoff
        console.log(`Rate limited, waiting ${delay}ms`);
        await new Promise(resolve => setTimeout(resolve, delay));
      } else {
        throw error;
      }
    }
  }
  throw new Error('Rate limit retries exhausted');
}

Prevention:

• Monitor rate limit headers
• Queue requests to stay under limits
• Upgrade provider tier if needed
• Implement request throttling

11. TypeScript Performance with Zod

Cause: Complex Zod schemas slow down TypeScript type checking.

Solution:

// Instead of deeply nested schemas at top level:
// const complexSchema = z.object({ /* 100+ fields */ });

// Define inside functions or use type assertions:
function generateData() {
  const schema = z.object({ /* complex schema */ });
  return generateObject({ model: openai('gpt-4-turbo'), schema, prompt: '...' });
}

// Or use z.lazy() for recursive schemas:
type Category = { name: string; subcategories?: Category[] };
const CategorySchema: z.ZodType<Category> = z.lazy(() =>
  z.object({
    name: z.string(),
    subcategories: z.array(CategorySchema).optional(),
  })
);

Prevention:

• Avoid top-level complex schemas
• Use z.lazy() for recursive types
• Split large schemas into smaller ones
• Use type assertions where appropriate

Official Docs: https://ai-sdk.dev/docs/troubleshooting/common-issues/slow-type-checking

12. Invalid JSON Response (Provider-Specific)

Cause: Some models occasionally return invalid JSON.

Solution:

// Use built-in retry and mode selection
const result = await generateObject({
  model: openai('gpt-4-turbo'),
  schema: mySchema,
  prompt: 'Generate data',
  mode: 'json',  // Force JSON mode (supported by GPT-4)
  maxRetries: 3,  // Retry on invalid JSON
});

// Or catch and retry manually:
try {
  const result = await generateObject({
    model: openai('gpt-4-turbo'),
    schema: mySchema,
    prompt: 'Generate data',
  });
} catch (error) {
  // Retry with different model
  const result = await generateObject({
    model: openai('gpt-4-turbo'),
    schema: mySchema,
    prompt: 'Generate data',
  });
}

Prevention:

• Use mode: 'json' when available
• Prefer GPT-4 for structured output
• Implement retry logic
• Validate responses

GitHub Issue: #4302 (Imagen 3.0 Invalid JSON)

13. Gemini Implicit Caching Fails with Tools

Error: No error, but higher API costs due to disabled caching Cause: Google Gemini 3 Flash's cost-saving implicit caching doesn't work when any tools are defined, even if never used. Source: GitHub Issue #11513

Why It Happens: Gemini API disables caching when tools are present in the request, regardless of whether they're invoked.

Prevention:

// Conditionally add tools only when needed
const needsTools = await analyzePrompt(userInput);

const result = await generateText({
  model: google('gemini-3-flash'),
  tools: needsTools ? { weather: weatherTool } : undefined,
  prompt: userInput,
});

Impact: High - Can significantly increase API costs for repeated context

14. Anthropic Tool Error Results Cause JSON Parse Crash

Error: SyntaxError: "[object Object]" is not valid JSON Cause: Anthropic provider built-in tools (web_fetch, etc.) return error objects that SDK tries to JSON.parse Source: GitHub Issue #11856

Why It Happens: When Anthropic built-in tools fail (e.g., url_not_allowed), they return error objects. AI SDK incorrectly tries to parse these as JSON strings.

Prevention:

try {
  const result = await generateText({
    model: anthropic('claude-sonnet-4-5-20250929'),
    tools: { web_fetch: { type: 'anthropic_defined', name: 'web_fetch' } },
    prompt: userPrompt,
  });
} catch (error) {
  if (error.message.includes('is not valid JSON')) {
    // Tool returned error result, handle gracefully
    console.error('Tool execution failed - likely blocked URL or permission issue');
    // Retry without tool or use custom tool
  }
  throw error;
}

Impact: High - Production crashes when using Anthropic built-in tools

15. Tool-Result in Assistant Message (Anthropic)

Error: Anthropic API error - tool-result in assistant message not allowed Cause: Server-executed tools incorrectly place tool-result parts in assistant messages Source: GitHub Issue #11855

Why It Happens: When using server-executed tools (tools where execute runs on server, not sent to model), the AI SDK incorrectly includes tool-result parts in the assistant message. Anthropic expects tool-result only in user messages.

Prevention:

// Workaround: Filter messages before sending
const filteredMessages = messages.map(msg => {
  if (msg.role === 'assistant') {
    return {
      ...msg,
      content: msg.content.filter(part => part.type !== 'tool-result'),
    };
  }
  return msg;
});

const result = await generateText({
  model: anthropic('claude-sonnet-4-5-20250929'),
  tools: { database: databaseTool },
  messages: filteredMessages,
  prompt: 'Get user data',
});

Impact: High - Breaks server-executed tool pattern with Anthropic provider

Status: Known issue, PR #11854 submitted

More Errors: https://ai-sdk.dev/docs/reference/ai-sdk-errors (31 total)

Known Issues & Limitations

useChat Stale Closures with Memoized Options

Issue: When using useChat with memoized options (common for performance), the onData and onFinish callbacks have stale closures and don't see updated state variables.

Source: GitHub Issue #11686

Reproduction:

const [count, setCount] = useState(0);

const chatOptions = useMemo(() => ({
  onFinish: (message) => {
    console.log('Count:', count); // ALWAYS 0, never updates!
  },
}), []); // Empty deps = stale closure

const { messages, append } = useChat(chatOptions);

Workaround 1 - Don't Memoize Callbacks:

const { messages, append } = useChat({
  onFinish: (message) => {
    console.log('Count:', count); // Now sees current count
  },
});

Workaround 2 - Use useRef:

const countRef = useRef(count);
useEffect(() => { countRef.current = count; }, [count]);

const chatOptions = useMemo(() => ({
  onFinish: (message) => {
    console.log('Count:', countRef.current); // Always current
  },
}), []);

Full Repro: https://github.com/alechoey/ai-sdk-stale-ondata-repro

Stream Resumption Fails on Tab Switch

Issue: When users switch browser tabs or background the app during an AI stream, the stream does not resume when they return. The connection is lost and does not automatically reconnect.

Source: GitHub Issue #11865

Impact: High - Major UX issue for long-running streams

Workaround 1 - Implement onError Handler:

const { messages, append, reload } = useChat({
  api: '/api/chat',
  onError: (error) => {
    if (error.message.includes('stream') || error.message.includes('aborted')) {
      // Attempt to reload last message
      reload();
    }
  },
});

Workaround 2 - Detect Visibility Change:

useEffect(() => {
  const handleVisibilityChange = () => {
    if (document.visibilityState === 'visible') {
      // Check if stream was interrupted
      const lastMessage = messages[messages.length - 1];
      if (lastMessage?.role === 'assistant' && !lastMessage.content) {
        reload();
      }
    }
  };

  document.addEventListener('visibilitychange', handleVisibilityChange);
  return () => document.removeEventListener('visibilitychange', handleVisibilityChange);
}, [messages, reload]);

Status: Known limitation, no auto-reconnection built-in

When to Use This Skill

Use ai-sdk-core when:

• Building backend AI features (server-side text generation)
• Implementing server-side text generation (Node.js, Workers, Next.js)
• Creating structured AI outputs (JSON, forms, data extraction)
• Building AI agents with tools (multi-step workflows)
• Integrating multiple AI providers (OpenAI, Anthropic, Google, Cloudflare)
• Migrating from AI SDK v4 to v5
• Encountering AI SDK errors (AI_APICallError, AI_NoObjectGeneratedError, etc.)
• Using AI in Cloudflare Workers (with workers-ai-provider)
• Using AI in Next.js Server Components/Actions
• Need consistent API across different LLM providers

Don't use this skill when:

• Building React chat UIs (use ai-sdk-ui skill instead)
• Need frontend hooks like useChat (use ai-sdk-ui skill instead)
• Need advanced topics like embeddings or image generation (check official docs)
• Building native Cloudflare Workers AI apps without multi-provider (use cloudflare-workers-ai skill instead)
• Need Generative UI / RSC (see https://ai-sdk.dev/docs/ai-sdk-rsc)

Versions

AI SDK:

• Stable: ai@6.0.26 (Jan 2026)
• ⚠️ Skip v6.0.40 - Breaking streaming change (reverted in v6.0.41)
• Legacy v5: ai@5.0.117 (ai-v5 tag)
• Zod 3.x/4.x both supported

Latest Models (2026):

• OpenAI: GPT-5.2, GPT-5.1, GPT-5, o3, o3-mini, o4-mini
• Anthropic: Claude Sonnet 4.5, Opus 4.1, Haiku 4.5
• Google: Gemini 2.5 Pro/Flash/Lite

Check Latest:

npm view ai version
npm view ai dist-tags

Official Docs

Core:

• AI SDK v6: https://ai-sdk.dev/docs
• AI SDK Core: https://ai-sdk.dev/docs/ai-sdk-core/overview
• Output API: https://ai-sdk.dev/docs/ai-sdk-core/generating-structured-data
• v4→v5 Migration: https://ai-sdk.dev/docs/migration-guides/migration-guide-5-0
• All Errors (31): https://ai-sdk.dev/docs/reference/ai-sdk-errors
• Providers (69+): https://ai-sdk.dev/providers/overview

Multi-Modal:

• Speech: https://ai-sdk.dev/docs/ai-sdk-core/speech
• Transcription: https://ai-sdk.dev/docs/ai-sdk-core/transcription
• Image Generation: https://ai-sdk.dev/docs/ai-sdk-core/image-generation
• Embeddings: https://ai-sdk.dev/docs/ai-sdk-core/embeddings

GitHub:

• Repository: https://github.com/vercel/ai
• Issues: https://github.com/vercel/ai/issues

Last Updated: 2026-01-20 Skill Version: 2.1.0 Changes: Added 3 new errors (Gemini caching, Anthropic tool errors, tool-result placement), MCP security guidance, tool approval best practices, React hooks edge cases, stream resumption workarounds AI SDK: 6.0.26 stable (avoid v6.0.40)