# AN-2026-0883: AI SDK 6: convertToModelMessages() is async (missing await: TS2740 Promise<ModelMessage[]>, runtime 'messages.some is not a function') and Tool.toModelOutput receives { output }

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- id: AN-2026-0883 (version 1; cite https://breakwire.org/claim/AN-2026-0883/v/1)
- kind: breaking · status: active · review: editor
- source: <https://ai-sdk.dev/docs/migration-guides/migration-guide-6-0#:~:text=is%20async%20in%20AI%20SDK%206>
- more sources: <https://github.com/vercel/ai/blob/main/content/docs/08-migration-guides/24-migration-guide-6-0.mdx> <https://raw.githubusercontent.com/microsoft/TypeScript/v5.9.3/src/compiler/diagnosticMessages.json>
- event date: 2025-12-22
- services: ai-sdk, nodejs, typescript
- affected: npm:ai >=6.0.0
- severity: medium
- 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 6.0 migration guide says convertToModelMessages() is async in AI SDK 6 (to support async Tool.toModelOutput()); calls need `await` (codemod add-await-converttomodelmessages). It also says toModelOutput() now receives a parameter object with an `output` property instead of the output itself (codemod wrap-tomodeloutput-parameter).  [✓0 ✗0]
1. Reproduced 2026-11-04 with ai 6.0.323: passing `convertToModelMessages(ui)` without await to streamText's `messages` gives tsc 5.9.3 error TS2740: Type 'Promise<ModelMessage[]>' is missing the following properties from type 'ModelMessage[]': length, pop, push, concat, and 29 more.; in plain JavaScript generateText throws TypeError: messages.some is not a function.  [✓0 ✗0]

## Fix
```text
Add `await` before every convertToModelMessages call (`npx @ai-sdk/codemod v6/add-await-converttomodelmessages src/`), and change `toModelOutput: output => ...` to `toModelOutput: ({ output }) => ...`.
```

## Error signatures
- substring: `Type 'Promise<ModelMessage[]>' is missing the following properties from type 'ModelMessage[]'` (tsc 5.9.3 TS2740 on ai 6.0.323)
- substring: `messages.some is not a function` (reproduced on ai 6.0.323 (generateText with an un-awaited convertToModelMessages promise))

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0883/reports_

## History
- v1 2026-11-05 by wire-editor: filed from primary source opened 2026-10-28 [lint override: TS2740 instance of the TypeScript template (cited); 'messages.some is not a function' is the V8 'is not a function' runtime text reproduced on ai 6.0.323 from an un-awaited convertToModelMessages prom]