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fix(ai): Unexpected reasoning-start event in extract reasoning middleware #7107

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lgrammel merged 1 commit into from
Jul 8, 2025
+95 −16
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fix(ai): Unexpected reasoning-start event in extract reasoning middleware #7107

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5 changes: 5 additions & 0 deletions .changeset/spotty-apples-call.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
'ai': patch
---

fix(ai): Unexpected reasoning-start event in extract reasoning middleware
100 changes: 87 additions & 13 deletions packages/ai/core/middleware/extract-reasoning-middleware.test.ts
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Expand Up @@ -683,20 +683,12 @@ describe('extractReasoningMiddleware', () => {
"id": "1",
"type": "text-start",
},
{
"id": "reasoning-0",
"type": "reasoning-start",
},
{
"id": "1",
"providerMetadata": undefined,
"text": "ana",
"type": "text",
},
{
"id": "reasoning-0",
"type": "reasoning-start",
},
{
"id": "1",
"providerMetadata": undefined,
Expand All @@ -705,18 +697,100 @@ describe('extractReasoningMiddleware', () => {
"type": "text",
},
{
"id": "reasoning-0",
"type": "reasoning-start",
"id": "1",
"providerMetadata": undefined,
"text": "</think>",
"type": "text",
},
Comment on lines +700 to 704
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@lgrammel lgrammel Jul 8, 2025

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should this be removed?

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@lgrammel lgrammel Jul 8, 2025

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(wondering if there is another bug hidden here)

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@DeJeune DeJeune Jul 8, 2025

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According to this test case and fix, when startWithReasoning equals false, only one reasoning-start event should be sent. Theoretically, there shouldn't be any bug.

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@lgrammel lgrammel Jul 8, 2025

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thanks for checking!

{
"id": "1",
"providerMetadata": undefined,
"text": "</think>",
"text": "this is the response",
"type": "text",
},
{
"id": "reasoning-0",
"type": "reasoning-start",
"id": "1",
"type": "text-end",
},
{
"finishReason": "stop",
"providerMetadata": undefined,
"response": {
"headers": undefined,
"id": "id-0",
"modelId": "mock-model-id",
"timestamp": 1970-01-01T00:00:00.000Z,
},
"type": "finish-step",
"usage": {
"cachedInputTokens": undefined,
"inputTokens": 5,
"outputTokens": 10,
"reasoningTokens": 3,
"totalTokens": 18,
},
},
{
"finishReason": "stop",
"totalUsage": {
"cachedInputTokens": undefined,
"inputTokens": 5,
"outputTokens": 10,
"reasoningTokens": 3,
"totalTokens": 18,
},
"type": "finish",
},
]
`);
});

it('should keep original text when <think> tag is not present', async () => {
const mockModel = new MockLanguageModelV2({
async doStream() {
return {
stream: convertArrayToReadableStream([
{
type: 'response-metadata',
id: 'id-0',
modelId: 'mock-model-id',
timestamp: new Date(0),
},
{ type: 'text-start', id: '1' },
{ type: 'text-delta', id: '1', delta: 'this is the response' },
{ type: 'text-end', id: '1' },
{
type: 'finish',
finishReason: 'stop',
usage: testUsage,
},
]),
};
},
});

const result = streamText({
model: wrapLanguageModel({
model: mockModel,
middleware: extractReasoningMiddleware({ tagName: 'think' }),
}),
prompt: 'Hello, how can I help?',
});

expect(await convertAsyncIterableToArray(result.fullStream))
.toMatchInlineSnapshot(`
[
{
"type": "start",
},
{
"request": {},
"type": "start-step",
"warnings": [],
},
{
"id": "1",
"type": "text-start",
},
{
"id": "1",
Expand Down
6 changes: 3 additions & 3 deletions packages/ai/core/middleware/extract-reasoning-middleware.ts
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Expand Up @@ -133,9 +133,9 @@ export function extractReasoningMiddleware({
: '';

if (
(activeExtraction.afterSwitch &&
activeExtraction.isReasoning) ||
activeExtraction.isFirstReasoning
activeExtraction.isReasoning &&
(activeExtraction.afterSwitch ||
activeExtraction.isFirstReasoning)
) {
controller.enqueue({
type: 'reasoning-start',
Expand Down
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