fix(core): Prevent `instrumentAnthropicAiClient` breaking MessageStream api #17754

andreiborza · 2025-09-24T12:40:04Z

Previously, we completely walked over anthropic's SDK and replaced message.stream with our own method that returns an async generator. This breaks the SDK as MessageStream has further user callable api, such as adding event handlers.

This fix proxies message.stream instead of replacing it with our own method. Instead of returning an async generator, we now hook into various events to do our instrumentation.

Streams requested via stream: true are expected to return async generators, so the current approach still holds, the only change is that we proxy instead of overwrite.

Fixes: #17734

github-actions · 2025-09-24T12:48:14Z

size-limit report 📦

⚠️ Warning: Base artifact is not the latest one, because the latest workflow run is not done yet. This may lead to incorrect results. Try to re-run all tests to get up to date results.

Path	Size	% Change	Change
@sentry/browser	24.26 kB	-	-
@sentry/browser - with treeshaking flags	22.77 kB	-	-
@sentry/browser (incl. Tracing)	40.43 kB	-	-
@sentry/browser (incl. Tracing, Replay)	78.81 kB	-	-
@sentry/browser (incl. Tracing, Replay) - with treeshaking flags	68.48 kB	-	-
@sentry/browser (incl. Tracing, Replay with Canvas)	83.48 kB	-	-
@sentry/browser (incl. Tracing, Replay, Feedback)	95.69 kB	-	-
@sentry/browser (incl. Feedback)	40.97 kB	-	-
@sentry/browser (incl. sendFeedback)	28.91 kB	-	-
@sentry/browser (incl. FeedbackAsync)	33.84 kB	-	-
@sentry/react	25.98 kB	-	-
@sentry/react (incl. Tracing)	42.41 kB	-	-
@sentry/vue	28.78 kB	-	-
@sentry/vue (incl. Tracing)	42.24 kB	-	-
@sentry/svelte	24.29 kB	-	-
CDN Bundle	25.77 kB	-	-
CDN Bundle (incl. Tracing)	40.33 kB	-	-
CDN Bundle (incl. Tracing, Replay)	76.56 kB	-	-
CDN Bundle (incl. Tracing, Replay, Feedback)	82.05 kB	-	-
CDN Bundle - uncompressed	75.37 kB	-	-
CDN Bundle (incl. Tracing) - uncompressed	119.39 kB	-	-
CDN Bundle (incl. Tracing, Replay) - uncompressed	234.51 kB	-	-
CDN Bundle (incl. Tracing, Replay, Feedback) - uncompressed	247.27 kB	-	-
@sentry/nextjs (client)	44.42 kB	-	-
@sentry/sveltekit (client)	40.85 kB	-	-
@sentry/node-core	50.02 kB	-0.01%	-1 B 🔽
@sentry/node	153.06 kB	+0.15%	+228 B 🔺
@sentry/node - without tracing	91.94 kB	-0.01%	-1 B 🔽
@sentry/aws-serverless	105.39 kB	-0.01%	-1 B 🔽

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github-actions · 2025-09-24T12:50:07Z

node-overhead report 🧳

Note: This is a synthetic benchmark with a minimal express app and does not necessarily reflect the real-world performance impact in an application.
⚠️ Warning: Base artifact is not the latest one, because the latest workflow run is not done yet. This may lead to incorrect results. Try to re-run all tests to get up to date results.

Scenario	Requests/s	% of Baseline	Prev. Requests/s	Change %
GET Baseline	8,877	-	9,257	-4%
GET With Sentry	1,383	16%	1,365	+1%
GET With Sentry (error only)	6,060	68%	6,221	-3%
POST Baseline	1,190	-	1,215	-2%
POST With Sentry	507	43%	553	-8%
POST With Sentry (error only)	1,051	88%	1,068	-2%
MYSQL Baseline	3,304	-	3,342	-1%
MYSQL With Sentry	439	13%	444	-1%
MYSQL With Sentry (error only)	2,671	81%	2,719	-2%

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mydea · 2025-09-24T13:13:05Z

packages/core/src/utils/anthropic-ai/index.ts

-    if (isStreamRequested || isStreamingMethod) {
-      return startSpanManual(
+      if (isStreamRequested || isStreamingMethod) {
+        const messageStream = target.apply(context, args);


m: I think (this is also what cursor is raising I believe) that this should move into the startSpanManual callback, so this is properly encapsulated by that span.

Ah yea, this should move down. Thanks.

mydea · 2025-09-24T13:14:10Z

packages/core/src/utils/anthropic-ai/index.ts

+                  },
+                },
+              });
+              span.end();


l/m: We should check if the span is not yet ended here, because it could be ended already from the main code path and throw afterwards in theory, I suppose?

mydea · 2025-09-24T13:15:44Z

packages/core/src/utils/anthropic-ai/streaming.ts

 */
-
-function processEvent(
+export function processEvent(


does this need to be exported?

Nope, leftover. Removed.

mydea · 2025-09-24T13:16:00Z

packages/core/src/utils/anthropic-ai/streaming.ts

 */
-
-interface StreamingState {
+export interface StreamingState {


does this need to be exported?

Nope, leftover from a previous approach 😅

mydea · 2025-09-24T13:16:05Z

packages/core/src/utils/anthropic-ai/streaming.ts

- * each event from the input stream unchanged.
+ * Finalizes span attributes when stream processing completes
+ */
+export function finalizeStreamSpan(state: StreamingState, span: Span, recordOutputs: boolean): void {


does this need to be exported?

Nope, leftover. Removed.

mydea · 2025-09-25T08:03:39Z

packages/core/src/utils/anthropic-ai/streaming.ts

+    });
+  }
+
+  if (span.isRecording()) {


l: We could also just check isRecording() at the top of the function and early return if not, setting attributes is a noop in that case anyhow :)

Updated, thanks!

mydea

nice, great catch and improvement here that there are these two paths, and nice tests 🚀

…am api

…ere it can end

….stream`

cursor · 2025-09-25T11:47:04Z

dev-packages/node-integration-tests/suites/tracing/anthropic/test.ts

+        op: 'gen_ai.messages',
+        origin: 'auto.ai.anthropic',
+        status: 'ok',
+      }),


Bug: Stream Attribute Mismatch in Test

The test for the messages.stream span incorrectly expects gen_ai.request.stream: true. This attribute is only set when an explicit stream parameter is passed, which messages.stream does not use as it's inherently streaming. The instrumentation correctly reflects this by omitting the attribute for messages.stream calls.

Not true, we add this in both cases.

andreiborza requested a review from mydea September 24, 2025 12:41

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andreiborza requested a review from mydea September 25, 2025 07:55

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andreiborza added 7 commits September 25, 2025 13:42

fix(core): Prevent instrumentAnthropicAiClient breaking MessageStre…

b33939e

…am api

Move target.apply down into startSpanManual

bf90b41

Remove unnecessary exports

23dae8b

Ensure span is recording before ending as there are multiple paths wh…

8267cfb

…ere it can end

Differentiate between handling of stream: true and `client.messages…

35a1a02

….stream`

Refactor

2c68a7c

Move recording check up and early return

894aa11

andreiborza force-pushed the ab/fix-anthropic-streaming branch from 9bf91c6 to 894aa11 Compare September 25, 2025 11:42

cursor bot reviewed Sep 25, 2025

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andreiborza merged commit f4df972 into develop Sep 25, 2025
188 checks passed

andreiborza deleted the ab/fix-anthropic-streaming branch September 25, 2025 13:46

github-actions bot mentioned this pull request Sep 29, 2025

Anthropic message stream events unhandled #17734

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This was referenced Sep 29, 2025

Bump @sentry/react from 8.55.0 to 10.16.0 Pouria-FOSSA/dependabot-metadata-test#65

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Bump @sentry/react from 8.55.0 to 10.17.0 Pouria-FOSSA/dependabot-metadata-test#66

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fix(core): Prevent instrumentAnthropicAiClient breaking MessageStream api #17754

fix(core): Prevent instrumentAnthropicAiClient breaking MessageStream api #17754

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size-limit report 📦

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Bug: Stream Attribute Mismatch in Test

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fix(core): Prevent `instrumentAnthropicAiClient` breaking MessageStream api #17754

fix(core): Prevent `instrumentAnthropicAiClient` breaking MessageStream api #17754

andreiborza commented Sep 24, 2025 •

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