diff --git a/packages/core/src/tracing/index.ts b/packages/core/src/tracing/index.ts
index 9b56045b37f3..57303947249b 100644
--- a/packages/core/src/tracing/index.ts
+++ b/packages/core/src/tracing/index.ts
@@ -1,5 +1,10 @@
 export { registerSpanErrorInstrumentation } from './errors';
-export { setCapturedScopesOnSpan, getCapturedScopesOnSpan } from './utils';
+export {
+  setCapturedScopesOnSpan,
+  getCapturedScopesOnSpan,
+  markSpanForOtelSourceInference,
+  spanShouldInferOtelSource,
+} from './utils';
 export { startIdleSpan, TRACING_DEFAULTS } from './idleSpan';
 export { SentrySpan } from './sentrySpan';
 export { SentryNonRecordingSpan } from './sentryNonRecordingSpan';
diff --git a/packages/core/src/tracing/sentrySpan.ts b/packages/core/src/tracing/sentrySpan.ts
index 84c78e73356d..8387c788d5fd 100644
--- a/packages/core/src/tracing/sentrySpan.ts
+++ b/packages/core/src/tracing/sentrySpan.ts
@@ -46,7 +46,7 @@ import { getDynamicSamplingContextFromSpan } from './dynamicSamplingContext';
 import { logSpanEnd } from './logSpans';
 import { timedEventsToMeasurements } from './measurement';
 import { hasSpanStreamingEnabled } from './spans/hasSpanStreamingEnabled';
-import { getCapturedScopesOnSpan } from './utils';
+import { getCapturedScopesOnSpan, spanShouldInferOtelSource } from './utils';
 
 const MAX_SPAN_COUNT = 1000;
 
@@ -200,7 +200,14 @@ export class SentrySpan implements Span {
    */
   public updateName(name: string): this {
     this._name = name;
-    this.setAttribute(SEMANTIC_ATTRIBUTE_SENTRY_SOURCE, 'custom');
+    // Renaming a span marks its name as explicitly chosen, so we stamp `custom`.
+    // The exception is spans created by SentryTraceProvider: those are branded for
+    // OTel-style source inference at span end (mirroring OTel SDK spans, which have
+    // no Sentry source concept), so instrumentations renaming them must not pin
+    // `custom` — applyOtelSpanData infers the correct source (e.g. 'route', 'task').
+    if (!spanShouldInferOtelSource(this)) {
+      this.setAttribute(SEMANTIC_ATTRIBUTE_SENTRY_SOURCE, 'custom');
+    }
     return this;
   }
 
diff --git a/packages/core/src/tracing/utils.ts b/packages/core/src/tracing/utils.ts
index 0c0417a71a90..9de3a6f4ae77 100644
--- a/packages/core/src/tracing/utils.ts
+++ b/packages/core/src/tracing/utils.ts
@@ -6,11 +6,21 @@ import { derefWeakRef, makeWeakRef, type MaybeWeakRef } from '../utils/weakRef';
 const SCOPE_ON_START_SPAN_FIELD = '_sentryScope';
 const ISOLATION_SCOPE_ON_START_SPAN_FIELD = '_sentryIsolationScope';
 
+// Brand marking a span whose `sentry.source` should be inferred OTel-style at span end (by
+// `applyOtelSpanData`) rather than pinned. `SentryTraceProvider` sets it on the spans it creates
+// so they behave like OTel SDK spans, which carry no Sentry source concept. We use `Symbol.for`
+// so the key is shared across duplicated copies of `@sentry/core`.
+const OTEL_SOURCE_INFERENCE_SPAN_FIELD = Symbol.for('sentry.otelSourceInference');
+
 type SpanWithScopes = Span & {
   [SCOPE_ON_START_SPAN_FIELD]?: Scope;
   [ISOLATION_SCOPE_ON_START_SPAN_FIELD]?: MaybeWeakRef<Scope>;
 };
 
+type SpanWithOtelSourceInference = Span & {
+  [OTEL_SOURCE_INFERENCE_SPAN_FIELD]?: boolean;
+};
+
 /** Store the scope & isolation scope for a span, which can the be used when it is finished. */
 export function setCapturedScopesOnSpan(span: Span | undefined, scope: Scope, isolationScope: Scope): void {
   if (span) {
@@ -33,3 +43,17 @@ export function getCapturedScopesOnSpan(span: Span): { scope?: Scope; isolationS
     isolationScope: derefWeakRef(spanWithScopes[ISOLATION_SCOPE_ON_START_SPAN_FIELD]),
   };
 }
+
+/**
+ * Mark a span as eligible for OTel-style `sentry.source` inference at span end.
+ * Set by `SentryTraceProvider` on the spans it creates; read by `SentrySpan.updateName()` and
+ * `applyOtelSpanData()`.
+ */
+export function markSpanForOtelSourceInference(span: Span): void {
+  addNonEnumerableProperty(span, OTEL_SOURCE_INFERENCE_SPAN_FIELD, true);
+}
+
+/** Whether a span is marked for OTel-style `sentry.source` inference (see {@link markSpanForOtelSourceInference}). */
+export function spanShouldInferOtelSource(span: Span): boolean {
+  return (span as SpanWithOtelSourceInference)[OTEL_SOURCE_INFERENCE_SPAN_FIELD] === true;
+}
diff --git a/packages/core/test/lib/tracing/sentrySpan.test.ts b/packages/core/test/lib/tracing/sentrySpan.test.ts
index 76b7186cd28f..dfb7840b4125 100644
--- a/packages/core/test/lib/tracing/sentrySpan.test.ts
+++ b/packages/core/test/lib/tracing/sentrySpan.test.ts
@@ -4,6 +4,7 @@ import { setCurrentClient } from '../../../src/sdk';
 import { SEMANTIC_ATTRIBUTE_SENTRY_SOURCE } from '../../../src/semanticAttributes';
 import { SentrySpan } from '../../../src/tracing/sentrySpan';
 import { SPAN_STATUS_ERROR } from '../../../src/tracing/spanstatus';
+import { markSpanForOtelSourceInference } from '../../../src/tracing/utils';
 import type { SpanJSON } from '../../../src/types/span';
 import { spanToJSON, TRACE_FLAG_NONE, TRACE_FLAG_SAMPLED } from '../../../src/utils/spanUtils';
 import { timestampInSeconds } from '../../../src/utils/time';
@@ -37,6 +38,27 @@ describe('SentrySpan', () => {
       expect(spanJson.description).toEqual('new name');
       expect(spanJson.data[SEMANTIC_ATTRIBUTE_SENTRY_SOURCE]).toEqual('custom');
     });
+
+    it('sets the source to custom when calling updateName on a span without a source', () => {
+      const span = new SentrySpan({ name: 'original name' });
+
+      span.updateName('new name');
+
+      const spanJson = spanToJSON(span);
+      expect(spanJson.description).toEqual('new name');
+      expect(spanJson.data[SEMANTIC_ATTRIBUTE_SENTRY_SOURCE]).toEqual('custom');
+    });
+
+    it('does not set the source when calling updateName on a span marked for OTel source inference', () => {
+      const span = new SentrySpan({ name: 'original name' });
+      markSpanForOtelSourceInference(span);
+
+      span.updateName('new name');
+
+      const spanJson = spanToJSON(span);
+      expect(spanJson.description).toEqual('new name');
+      expect(spanJson.data[SEMANTIC_ATTRIBUTE_SENTRY_SOURCE]).toBeUndefined();
+    });
   });
 
   describe('setters', () => {