--- title: Migrate AI SDK 4.1 to 4.2 description: Learn how to upgrade AI SDK 4.1 to 4.2. --- # Migrate AI SDK 4.1 to 4.2 Check out the [AI SDK 4.2 release blog post](https://vercel.com/blog/ai-sdk-4-2) for more information about the release. This guide will help you upgrade to AI SDK 4.2: ## Stable APIs The following APIs have been moved to stable and no longer have the `experimental_` prefix: - `customProvider` - `providerOptions` (renamed from `providerMetadata` for provider-specific inputs) - `providerMetadata` (for provider-specific outputs) - `toolCallStreaming` option for `streamText` ## Dependency Versions AI SDK requires a non-optional `zod` dependency with version `^3.23.8`. ## UI Message Parts In AI SDK 4.2, we've redesigned how `useChat` handles model outputs with message parts and multiple steps. This is a significant improvement that simplifies rendering complex, multi-modal AI responses in your UI. ### What's Changed Assistant messages with tool calling now get combined into a single message with multiple parts, rather than creating separate messages for each step. This change addresses two key developments in AI applications: 1. **Diverse Output Types**: Models now generate more than just text; they produce reasoning steps, sources, and tool calls. 2. **Interleaved Outputs**: In multi-step agent use-cases, these different output types are frequently interleaved. ### Benefits of the New Approach Previously, `useChat` stored different output types separately, which made it challenging to maintain the correct sequence in your UI when these elements were interleaved in a response, and led to multiple consecutive assistant messages when there were tool calls. For example: ```javascript message.content = "Final answer: 42"; message.reasoning = "First I'll calculate X, then Y..."; message.toolInvocations = [{toolName: "calculator", args: {...}}]; ``` This structure was limiting. The new message parts approach replaces separate properties with an ordered array that preserves the exact sequence: ```javascript message.parts = [ { type: "text", text: "Final answer: 42" }, { type: "reasoning", reasoning: "First I'll calculate X, then Y..." }, { type: "tool-invocation", toolInvocation: { toolName: "calculator", args: {...} } }, ]; ``` ### Migration Existing applications using the previous message format will need to update their UI components to handle the new `parts` array. The fields from the previous format are still available for backward compatibility, but we recommend migrating to the new format for better support of multi-modal and multi-step interactions. You can use the `useChat` hook with the new message parts as follows: ```javascript function Chat() { const { messages } = useChat(); return (

{messages.map(message => message.parts.map((part, i) => { switch (part.type) { case 'text': return

{part.text}

; case 'source': return

{part.source.url}

; case 'reasoning': return

{part.reasoning}

; case 'tool-invocation': return

{part.toolInvocation.toolName}

; case 'file': return (

); } }), )}

); } ```