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feat(ui): add finishReason in useChat onFinish callback #9857

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304d204
feat(react): add finishReason to useChat onFinish callback
KirschX Oct 28, 2025
bfc5b40
chore: remove unused import
KirschX Oct 29, 2025
8c86ab7
chore: updated finishReason related fixtures in chat.test
KirschX Oct 29, 2025
fe0f666
chore: update example
KirschX Oct 30, 2025
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6 changes: 6 additions & 0 deletions .changeset/six-roses-peel.md
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@@ -0,0 +1,6 @@
---
'@ai-sdk/react': patch
'ai': patch
---

Added finishReason on useChat onFinish callbck
9 changes: 8 additions & 1 deletion examples/next-openai/app/use-chat-data-ui-parts/page.tsx
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Expand Up @@ -2,7 +2,8 @@

import ChatInput from '@/components/chat-input';
import { useChat } from '@ai-sdk/react';
import { DefaultChatTransport, UIMessage } from 'ai';
import { DefaultChatTransport, UIMessage, type FinishReason } from 'ai';
import { useState } from 'react';

type MyMessage = UIMessage<
never,
Expand All @@ -16,6 +17,7 @@ type MyMessage = UIMessage<
>;

export default function Chat() {
const [lastFinishReason, setLastFinishReason] = useState<FinishReason | undefined>(undefined);
const { error, status, sendMessage, messages, regenerate, stop } =
useChat<MyMessage>({
transport: new DefaultChatTransport({
Expand All @@ -24,6 +26,9 @@ export default function Chat() {
onData: dataPart => {
console.log('dataPart', JSON.stringify(dataPart, null, 2));
},
onFinish: ({ finishReason }) => {
setLastFinishReason(finishReason);
},
});

return (
Expand Down Expand Up @@ -94,6 +99,8 @@ export default function Chat() {
</div>
)}

{messages.length > 0 && <div className="mt-4 text-gray-500">Finish reason: {String(lastFinishReason)}</div>}

<ChatInput status={status} onSubmit={text => sendMessage({ text })} />
</div>
);
Expand Down
1 change: 1 addition & 0 deletions packages/ai/src/generate-text/stream-text.ts
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Expand Up @@ -2153,6 +2153,7 @@ However, the LLM results are expected to be small enough to not cause issues.
if (sendFinish) {
controller.enqueue({
type: 'finish',
finishReason: part.finishReason,
...(messageMetadataValue != null
? { messageMetadata: messageMetadataValue }
: {}),
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1 change: 1 addition & 0 deletions packages/ai/src/ui-message-stream/handle-ui-message-stream-finish.ts
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Expand Up @@ -106,6 +106,7 @@ export function handleUIMessageStreamFinish<UI_MESSAGE extends UIMessage>({
...(isContinuation ? originalMessages.slice(0, -1) : originalMessages),
state.message,
] as UI_MESSAGE[],
finishReason: state.finishReason,
});
};

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13 changes: 13 additions & 0 deletions packages/ai/src/ui-message-stream/ui-message-chunks.ts
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Expand Up @@ -3,6 +3,7 @@ import {
ProviderMetadata,
providerMetadataSchema,
} from '../types/provider-metadata';
import { FinishReason } from '../types/language-model';
import {
InferUIMessageData,
InferUIMessageMetadata,
Expand Down Expand Up @@ -153,6 +154,17 @@ export const uiMessageChunkSchema = lazySchema(() =>
}),
z.strictObject({
type: z.literal('finish'),
finishReason: z
.enum([
'stop',
'length',
'content-filter',
'tool-calls',
'error',
'other',
'unknown',
] as const satisfies readonly FinishReason[])
.optional(),
messageMetadata: z.unknown().optional(),
}),
z.strictObject({
Expand Down Expand Up @@ -308,6 +320,7 @@ export type UIMessageChunk<
}
| {
type: 'finish';
finishReason?: FinishReason;
messageMetadata?: METADATA;
}
| {
Expand Down
6 changes: 6 additions & 0 deletions packages/ai/src/ui-message-stream/ui-message-stream-on-finish-callback.ts
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@@ -1,3 +1,4 @@
import { FinishReason } from '../types/language-model';
import { UIMessage } from '../ui/ui-messages';

export type UIMessageStreamOnFinishCallback<UI_MESSAGE extends UIMessage> =
Expand All @@ -23,4 +24,9 @@ export type UIMessageStreamOnFinishCallback<UI_MESSAGE extends UIMessage> =
* (including the original message if it was extended).
*/
responseMessage: UI_MESSAGE;

/**
* The reason why the generation finished.
*/
finishReason?: FinishReason;
}) => PromiseLike<void> | void;
13 changes: 8 additions & 5 deletions packages/ai/src/ui/chat.test.ts
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Expand Up @@ -96,7 +96,7 @@ describe('Chat', () => {
formatChunk({ type: 'text-delta', id: 'text-1', delta: '.' }),
formatChunk({ type: 'text-end', id: 'text-1' }),
formatChunk({ type: 'finish-step' }),
formatChunk({ type: 'finish' }),
formatChunk({ type: 'finish', finishReason: 'stop' }),
],
};

Expand Down Expand Up @@ -126,6 +126,7 @@ describe('Chat', () => {
expect(letOnFinishArgs).toMatchInlineSnapshot(`
[
{
"finishReason": "stop",
"isAbort": false,
"isDisconnect": false,
"isError": false,
Expand Down Expand Up @@ -484,6 +485,7 @@ describe('Chat', () => {
expect(letOnFinishArgs).toMatchInlineSnapshot(`
[
{
"finishReason": undefined,
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@gr2m gr2m Oct 28, 2025

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I haven't looked in detail yet, but is there a case where finishReason would be undefined? We might need to update our fixtures in the tests

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@KirschX KirschX Oct 29, 2025

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I think so, finishReason can be undefined when there’s no finish event (abort, disconnect, server error). For normal completions it should be set (usually 'stop').

I’ve updated fixtures: normal paths include finishReason: 'stop'; abnormal paths keep it undefined.

"isAbort": false,
"isDisconnect": true,
"isError": true,
Expand Down Expand Up @@ -719,6 +721,7 @@ describe('Chat', () => {
expect(letOnFinishArgs).toMatchInlineSnapshot(`
[
{
"finishReason": undefined,
"isAbort": true,
"isDisconnect": false,
"isError": false,
Expand Down Expand Up @@ -900,7 +903,7 @@ describe('Chat', () => {
}),
formatChunk({ type: 'text-end', id: 'text-1' }),
formatChunk({ type: 'finish-step' }),
formatChunk({ type: 'finish' }),
formatChunk({ type: 'finish', finishReason: 'stop' }),
],
};

Expand Down Expand Up @@ -1553,7 +1556,7 @@ describe('Chat', () => {

// finish stream
controller1.write(formatChunk({ type: 'finish-step' }));
controller1.write(formatChunk({ type: 'finish' }));
controller1.write(formatChunk({ type: 'finish', finishReason: 'stop' }));

await controller1.close();

Expand Down Expand Up @@ -1920,7 +1923,7 @@ describe('Chat', () => {
}),
formatChunk({ type: 'text-end', id: 'id-1' }),
formatChunk({ type: 'finish-step' }),
formatChunk({ type: 'finish' }),
formatChunk({ type: 'finish', finishReason: 'stop' }),
],
},
];
Expand Down Expand Up @@ -2423,7 +2426,7 @@ describe('Chat', () => {
}),
formatChunk({ type: 'text-end', id: 'txt-1' }),
formatChunk({ type: 'finish-step' }),
formatChunk({ type: 'finish' }),
formatChunk({ type: 'finish', finishReason: 'stop' }),
],
},
];
Expand Down
4 changes: 4 additions & 0 deletions packages/ai/src/ui/chat.ts
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Expand Up @@ -4,6 +4,7 @@ import {
IdGenerator,
InferSchema,
} from '@ai-sdk/provider-utils';
import { FinishReason } from '../types/language-model';
import { UIMessageChunk } from '../ui-message-stream/ui-message-chunks';
import { consumeStream } from '../util/consume-stream';
import { SerialJobExecutor } from '../util/serial-job-executor';
Expand Down Expand Up @@ -123,13 +124,15 @@ export type ChatOnDataCallback<UI_MESSAGE extends UIMessage> = (
* @param isAbort Indicates whether the request has been aborted.
* @param isDisconnect Indicates whether the request has been ended by a network error.
* @param isError Indicates whether the request has been ended by an error.
* @param finishReason The reason why the generation finished.
*/
export type ChatOnFinishCallback<UI_MESSAGE extends UIMessage> = (options: {
message: UI_MESSAGE;
messages: UI_MESSAGE[];
isAbort: boolean;
isDisconnect: boolean;
isError: boolean;
finishReason?: FinishReason;
}) => void;

export interface ChatInit<UI_MESSAGE extends UIMessage> {
Expand Down Expand Up @@ -685,6 +688,7 @@ export abstract class AbstractChat<UI_MESSAGE extends UIMessage> {
isAbort,
isDisconnect,
isError,
finishReason: this.activeResponse?.state.finishReason,
});
} catch (err) {
console.error(err);
Expand Down
5 changes: 5 additions & 0 deletions packages/ai/src/ui/process-ui-message-stream.ts
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@@ -1,5 +1,6 @@
import { FlexibleSchema, validateTypes } from '@ai-sdk/provider-utils';
import { ProviderMetadata } from '../types';
import { FinishReason } from '../types/language-model';
import {
DataUIMessageChunk,
InferUIMessageChunk,
Expand Down Expand Up @@ -41,6 +42,7 @@ export type StreamingUIMessageState<UI_MESSAGE extends UIMessage> = {
title?: string;
}
>;
finishReason?: FinishReason;
};

export function createStreamingUIMessageState<UI_MESSAGE extends UIMessage>({
Expand Down Expand Up @@ -635,6 +637,9 @@ export function processUIMessageStream<UI_MESSAGE extends UIMessage>({
}

case 'finish': {
if (chunk.finishReason != null) {
state.finishReason = chunk.finishReason;
}
await updateMessageMetadata(chunk.messageMetadata);
if (chunk.messageMetadata != null) {
write();
Expand Down
22 changes: 20 additions & 2 deletions packages/react/src/use-chat.ui.test.tsx
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Expand Up @@ -10,6 +10,7 @@ import { screen, waitFor } from '@testing-library/react';
import userEvent from '@testing-library/user-event';
import {
DefaultChatTransport,
FinishReason,
isToolUIPart,
TextStreamChatTransport,
UIMessage,
Expand Down Expand Up @@ -84,7 +85,14 @@ describe('initial messages', () => {
});

describe('data protocol stream', () => {
let onFinishCalls: Array<{ message: UIMessage }> = [];
let onFinishCalls: Array<{
message: UIMessage;
messages: UIMessage[];
isAbort: boolean;
isDisconnect: boolean;
isError: boolean;
finishReason?: FinishReason;
}> = [];

setupTestComponent(
({ id: idParam }: { id: string }) => {
Expand Down Expand Up @@ -304,6 +312,7 @@ describe('data protocol stream', () => {
controller.write(
formatChunk({
type: 'finish',
finishReason: 'stop',
messageMetadata: {
example: 'metadata',
},
Expand Down Expand Up @@ -346,6 +355,7 @@ describe('data protocol stream', () => {
expect(onFinishCalls).toMatchInlineSnapshot(`
[
{
"finishReason": "stop",
"isAbort": false,
"isDisconnect": false,
"isError": false,
Expand Down Expand Up @@ -436,7 +446,14 @@ describe('data protocol stream', () => {
});

describe('text stream', () => {
let onFinishCalls: Array<{ message: UIMessage }> = [];
let onFinishCalls: Array<{
message: UIMessage;
messages: UIMessage[];
isAbort: boolean;
isDisconnect: boolean;
isError: boolean;
finishReason?: FinishReason;
}> = [];

setupTestComponent(() => {
const { messages, sendMessage } = useChat({
Expand Down Expand Up @@ -537,6 +554,7 @@ describe('text stream', () => {
expect(onFinishCalls).toMatchInlineSnapshot(`
[
{
"finishReason": undefined,
"isAbort": false,
"isDisconnect": false,
"isError": false,
Expand Down