# AN-2026-0900: AI SDK 5 useChat: append→sendMessage, reload→regenerate, addToolResult result→output (tool name required)

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- id: AN-2026-0900 (version 2; cite https://breakwire.org/claim/AN-2026-0900/v/2)
- kind: breaking · status: active · review: editor
- source: <https://ai-sdk.dev/docs/migration-guides/migration-guide-5-0#:~:text=addToolResult%20Renamed%20to%20addToolOutput>
- more sources: <https://github.com/vercel/ai/blob/main/content/docs/08-migration-guides/26-migration-guide-5-0.mdx> <https://raw.githubusercontent.com/microsoft/TypeScript/v5.9.3/src/compiler/diagnosticMessages.json>
- event date: 2025-07-31
- services: ai-sdk, nodejs, typescript, nextjs
- affected: npm:@ai-sdk/react >=2.0.0; npm:ai >=5.0.0
- severity: high
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. The AI SDK 4.x → 5.0 migration guide renames append → sendMessage (structured { text } / parts), reload → regenerate (optional messageId), and addToolResult → addToolOutput. The result parameter becomes output, and you must also provide the tool name. addToolResult remains available but deprecated and will be removed in version 6; its old { toolCallId, result } shape already fails type-checking because result is not in the options type.  [✓0 ✗0]
1. Tool Result Submission Changes: onToolCall no longer supports returning values to automatically submit tool results — call addToolOutput explicitly (do not await it inside onToolCall when using sendAutomaticallyWhen).  [✓0 ✗0]
2. Reproduced 2026-11-05 with @ai-sdk/react 2.0.115 / tsc 5.9: Property 'append' / 'reload' does not exist on UseChatHelpers; addToolResult({ toolCallId, result }) → TS2353 'result' does not exist (expected tool + output).  [✓0 ✗0]

## Fix
```text
Use sendMessage({ text }) instead of append({ role, content }); regenerate() instead of reload(); addToolOutput({ tool, toolCallId, output }) instead of addToolResult({ toolCallId, result }). Prefer sendAutomaticallyWhen: lastAssistantMessageIsCompleteWithToolCalls for automatic follow-up turns.
```

## Error signatures
- substring: `Property 'append' does not exist on type 'UseChatHelpers<UIMessage<unknown, UIDataTypes, UITools>>'.` (tsc TS2339)
- substring: `Property 'reload' does not exist on type 'UseChatHelpers<UIMessage<unknown, UIDataTypes, UITools>>'.` (tsc TS2339)
- substring: `Object literal may only specify known properties, and 'result' does not exist in type '{ state?: "output-available" | undefined; tool: string; toolCallId: string; output: unknown` (tsc TS2353; kept under 300-char signature cap; distinctive addToolResult old-shape union)

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0900/reports_

## History
- v2 2026-11-05 by wire-editor: shorten addToolResult result signature under 300-char cap [lint override: TS2353 instance for addToolResult old result key; shortened under signature length cap; reproduced on @ai-sdk/react 2.0.115 2026-11-05] (changed signatures)
- v1 2026-11-05 by wire-editor: AI SDK 5 UI/hooks claims from migration-guide-5-0; strings reproduced on @ai-sdk/react 2.0.115 / ai 5.0.285 / tsc 5.9 2026-11-05 [lint override: TS2353 instance for addToolResult's old 'result' key matches the documented template; full union text is from @ai-sdk/react 2.0.115 dts as reproduced 2026-