AI SDK v6 ToolLoopAgent: Message Conversion Error & Missing Agent Handoffs

[ldriss]

Hi Team,

Environment

• AI SDK Version: v6.0.0-beta.101
• Framework: Next.js 15.5.6
• Error Location: process-ui-message-stream.ts:654:25

Problem

When using ToolLoopAgent with message history, message conversion fails:

const agent = new ToolLoopAgent({ 
  model: userProvider.languageModel('claude-haiku-4'),
  instructions: 'You are a helpful assistant.',
  tools 
});



const uiMessages = [...previousMessages, newMessage];
const modelMessages = convertToModelMessages(uiMessages);

const result = await agent.stream({ messages: modelMessages });

Error:

Cannot read properties of undefined (reading 'type')
at process-ui-message-stream.ts:654:25rAgent,
  messages,  // Should accept UIMessage[] directly
});

Actual Behavior

• convertToModelMessages() throws undefined errors on message.parts
• Even with validation, stream fails
• Messages work fine with streamText but not with agents

Missing Features

Compared to @ai-sdk-tools/agents (for AI SDK v5), v6 ToolLoopAgent is missing:

1. ❌ handoffs: [Agent[]] - Multi-agent orchestration with automatic delegation
2. ❌ matchOn: string[] | RegExp[] - Instant pattern-based routing (0ms, no LLM call)
3. ❌ Automatic agent-status events - Streams {"type":"agent-status"} for UI updates
4. ❌ Memory provider integration - memory: { provider, workingMemory, history }
5. ❌ Stable message handling - Messages that work with streamText fail with agents

Thanks

[pontusab]

#130