diff --git a/dev-packages/node-integration-tests/suites/tracing/anthropic/instrument-with-truncation.mjs b/dev-packages/node-integration-tests/suites/tracing/anthropic/instrument-with-truncation.mjs
new file mode 100644
index 000000000000..2adcdd009640
--- /dev/null
+++ b/dev-packages/node-integration-tests/suites/tracing/anthropic/instrument-with-truncation.mjs
@@ -0,0 +1,19 @@
+import * as Sentry from '@sentry/node';
+import { loggingTransport } from '@sentry-internal/node-integration-tests';
+
+Sentry.init({
+  dsn: 'https://public@dsn.ingest.sentry.io/1337',
+  release: '1.0',
+  tracesSampleRate: 1.0,
+  dataCollection: { genAI: { inputs: true, outputs: true } },
+  transport: loggingTransport,
+  integrations: [Sentry.anthropicAIIntegration({ enableTruncation: true })],
+  beforeSendTransaction: event => {
+    // Filter out mock express server transactions
+    if (event.transaction.includes('/anthropic/v1/')) {
+      return null;
+    }
+    return event;
+  },
+  streamGenAiSpans: true,
+});
diff --git a/dev-packages/node-integration-tests/suites/tracing/anthropic/scenario-media-truncation.mjs b/dev-packages/node-integration-tests/suites/tracing/anthropic/scenario-media-truncation.mjs
index 7df934404ff9..ce5253cc34d7 100644
--- a/dev-packages/node-integration-tests/suites/tracing/anthropic/scenario-media-truncation.mjs
+++ b/dev-packages/node-integration-tests/suites/tracing/anthropic/scenario-media-truncation.mjs
@@ -46,7 +46,7 @@ async function run() {
       apiKey: 'mock-api-key',
     });
 
-    const client = instrumentAnthropicAiClient(mockClient);
+    const client = instrumentAnthropicAiClient(mockClient, { enableTruncation: true, recordInputs: true });
 
     // Send the image showing the number 3
     // Put the image in the last message so it doesn't get dropped
diff --git a/dev-packages/node-integration-tests/suites/tracing/anthropic/scenario-message-truncation.mjs b/dev-packages/node-integration-tests/suites/tracing/anthropic/scenario-message-truncation.mjs
index 49cee7e3067d..15711d019e2a 100644
--- a/dev-packages/node-integration-tests/suites/tracing/anthropic/scenario-message-truncation.mjs
+++ b/dev-packages/node-integration-tests/suites/tracing/anthropic/scenario-message-truncation.mjs
@@ -46,7 +46,7 @@ async function run() {
       apiKey: 'mock-api-key',
     });
 
-    const client = instrumentAnthropicAiClient(mockClient);
+    const client = instrumentAnthropicAiClient(mockClient, { enableTruncation: true, recordInputs: true });
 
     // Test 1: Given an array of messages only the last message should be kept
     // The last message should be truncated to fit within the 20KB limit
diff --git a/dev-packages/node-integration-tests/suites/tracing/anthropic/test.ts b/dev-packages/node-integration-tests/suites/tracing/anthropic/test.ts
index e29ce5514494..96760bb10e9f 100644
--- a/dev-packages/node-integration-tests/suites/tracing/anthropic/test.ts
+++ b/dev-packages/node-integration-tests/suites/tracing/anthropic/test.ts
@@ -606,7 +606,7 @@ describe('Anthropic integration', () => {
   createEsmAndCjsTests(
     __dirname,
     'scenario-message-truncation.mjs',
-    'instrument-with-pii.mjs',
+    'instrument-with-truncation.mjs',
     (createRunner, test) => {
       test('truncates messages when they exceed byte limit - keeps only last message and crops it', async () => {
         await createRunner()
@@ -659,51 +659,56 @@ describe('Anthropic integration', () => {
     },
   );
 
-  createEsmAndCjsTests(__dirname, 'scenario-media-truncation.mjs', 'instrument-with-pii.mjs', (createRunner, test) => {
-    test('truncates media attachment, keeping all other details', async () => {
-      const expectedMediaMessages = JSON.stringify([
-        {
-          role: 'user',
-          content: [
-            {
-              type: 'image',
-              source: {
-                type: 'base64',
-                media_type: 'image/png',
-                data: '[Blob substitute]',
+  createEsmAndCjsTests(
+    __dirname,
+    'scenario-media-truncation.mjs',
+    'instrument-with-truncation.mjs',
+    (createRunner, test) => {
+      test('truncates media attachment, keeping all other details', async () => {
+        const expectedMediaMessages = JSON.stringify([
+          {
+            role: 'user',
+            content: [
+              {
+                type: 'image',
+                source: {
+                  type: 'base64',
+                  media_type: 'image/png',
+                  data: '[Blob substitute]',
+                },
               },
-            },
-          ],
-        },
-      ]);
-      await createRunner()
-        .ignore('event')
-        .expect({
-          transaction: {
-            transaction: 'main',
+            ],
           },
-        })
-        .expect({
-          span: container => {
-            expect(container.items).toHaveLength(1);
-            const [firstSpan] = container.items;
+        ]);
+        await createRunner()
+          .ignore('event')
+          .expect({
+            transaction: {
+              transaction: 'main',
+            },
+          })
+          .expect({
+            span: container => {
+              expect(container.items).toHaveLength(1);
+              const [firstSpan] = container.items;
 
-            // [0] messages.create with media attachment — image data replaced, other fields preserved
-            expect(firstSpan!.name).toBe('chat claude-3-haiku-20240307');
-            expect(firstSpan!.status).toBe('ok');
-            expect(firstSpan!.attributes[GEN_AI_INPUT_MESSAGES_ATTRIBUTE].value).toBe(expectedMediaMessages);
-            expect(firstSpan!.attributes[GEN_AI_OPERATION_NAME_ATTRIBUTE].value).toBe('chat');
-            expect(firstSpan!.attributes['sentry.op'].value).toBe('gen_ai.chat');
-            expect(firstSpan!.attributes['sentry.origin'].value).toBe('auto.ai.anthropic');
-            expect(firstSpan!.attributes[GEN_AI_SYSTEM_ATTRIBUTE].value).toBe('anthropic');
-            expect(firstSpan!.attributes[GEN_AI_REQUEST_MODEL_ATTRIBUTE].value).toBe('claude-3-haiku-20240307');
-            expect(firstSpan!.attributes[GEN_AI_INPUT_MESSAGES_ORIGINAL_LENGTH_ATTRIBUTE].value).toBe(2);
-          },
-        })
-        .start()
-        .completed();
-    });
-  });
+              // [0] messages.create with media attachment — image data replaced, other fields preserved
+              expect(firstSpan!.name).toBe('chat claude-3-haiku-20240307');
+              expect(firstSpan!.status).toBe('ok');
+              expect(firstSpan!.attributes[GEN_AI_INPUT_MESSAGES_ATTRIBUTE].value).toBe(expectedMediaMessages);
+              expect(firstSpan!.attributes[GEN_AI_OPERATION_NAME_ATTRIBUTE].value).toBe('chat');
+              expect(firstSpan!.attributes['sentry.op'].value).toBe('gen_ai.chat');
+              expect(firstSpan!.attributes['sentry.origin'].value).toBe('auto.ai.anthropic');
+              expect(firstSpan!.attributes[GEN_AI_SYSTEM_ATTRIBUTE].value).toBe('anthropic');
+              expect(firstSpan!.attributes[GEN_AI_REQUEST_MODEL_ATTRIBUTE].value).toBe('claude-3-haiku-20240307');
+              expect(firstSpan!.attributes[GEN_AI_INPUT_MESSAGES_ORIGINAL_LENGTH_ATTRIBUTE].value).toBe(2);
+            },
+          })
+          .start()
+          .completed();
+      });
+    },
+  );
 
   createEsmAndCjsTests(
     __dirname,
diff --git a/dev-packages/node-integration-tests/suites/tracing/google-genai/instrument-with-truncation.mjs b/dev-packages/node-integration-tests/suites/tracing/google-genai/instrument-with-truncation.mjs
new file mode 100644
index 000000000000..895e7d2ffbad
--- /dev/null
+++ b/dev-packages/node-integration-tests/suites/tracing/google-genai/instrument-with-truncation.mjs
@@ -0,0 +1,19 @@
+import * as Sentry from '@sentry/node';
+import { loggingTransport } from '@sentry-internal/node-integration-tests';
+
+Sentry.init({
+  dsn: 'https://public@dsn.ingest.sentry.io/1337',
+  release: '1.0',
+  tracesSampleRate: 1.0,
+  dataCollection: { genAI: { inputs: true, outputs: true } },
+  transport: loggingTransport,
+  integrations: [Sentry.googleGenAIIntegration({ enableTruncation: true })],
+  beforeSendTransaction: event => {
+    // Filter out mock express server transactions
+    if (event.transaction.includes('/v1beta/')) {
+      return null;
+    }
+    return event;
+  },
+  streamGenAiSpans: true,
+});
diff --git a/dev-packages/node-integration-tests/suites/tracing/google-genai/scenario-message-truncation.mjs b/dev-packages/node-integration-tests/suites/tracing/google-genai/scenario-message-truncation.mjs
index 595728e06531..e6146214d7fe 100644
--- a/dev-packages/node-integration-tests/suites/tracing/google-genai/scenario-message-truncation.mjs
+++ b/dev-packages/node-integration-tests/suites/tracing/google-genai/scenario-message-truncation.mjs
@@ -41,7 +41,7 @@ async function run() {
       apiKey: 'mock-api-key',
     });
 
-    const client = instrumentGoogleGenAIClient(mockClient);
+    const client = instrumentGoogleGenAIClient(mockClient, { enableTruncation: true, recordInputs: true });
 
     // Test 1: Given an array of messages only the last message should be kept
     // The last message should be truncated to fit within the 20KB limit
diff --git a/dev-packages/node-integration-tests/suites/tracing/google-genai/test.ts b/dev-packages/node-integration-tests/suites/tracing/google-genai/test.ts
index 2aad9237cd22..a172fdaa27a5 100644
--- a/dev-packages/node-integration-tests/suites/tracing/google-genai/test.ts
+++ b/dev-packages/node-integration-tests/suites/tracing/google-genai/test.ts
@@ -347,7 +347,7 @@ describe('Google GenAI integration', () => {
   createEsmAndCjsTests(
     __dirname,
     'scenario-message-truncation.mjs',
-    'instrument-with-pii.mjs',
+    'instrument-with-truncation.mjs',
     (createRunner, test) => {
       test('truncates messages when they exceed byte limit - keeps only last message and crops it', async () => {
         await createRunner()
diff --git a/dev-packages/node-integration-tests/suites/tracing/langchain/instrument-with-truncation.mjs b/dev-packages/node-integration-tests/suites/tracing/langchain/instrument-with-truncation.mjs
new file mode 100644
index 000000000000..f402bce82071
--- /dev/null
+++ b/dev-packages/node-integration-tests/suites/tracing/langchain/instrument-with-truncation.mjs
@@ -0,0 +1,19 @@
+import * as Sentry from '@sentry/node';
+import { loggingTransport } from '@sentry-internal/node-integration-tests';
+
+Sentry.init({
+  dsn: 'https://public@dsn.ingest.sentry.io/1337',
+  release: '1.0',
+  tracesSampleRate: 1.0,
+  dataCollection: { genAI: { inputs: true, outputs: true } },
+  transport: loggingTransport,
+  integrations: [Sentry.langChainIntegration({ enableTruncation: true })],
+  beforeSendTransaction: event => {
+    // Filter out mock express server transactions
+    if (event.transaction.includes('/v1/messages') || event.transaction.includes('/v1/embeddings')) {
+      return null;
+    }
+    return event;
+  },
+  streamGenAiSpans: true,
+});
diff --git a/dev-packages/node-integration-tests/suites/tracing/langchain/test.ts b/dev-packages/node-integration-tests/suites/tracing/langchain/test.ts
index 3e3ba9490c86..729be314e5fb 100644
--- a/dev-packages/node-integration-tests/suites/tracing/langchain/test.ts
+++ b/dev-packages/node-integration-tests/suites/tracing/langchain/test.ts
@@ -199,7 +199,7 @@ describe('LangChain integration', () => {
   createEsmAndCjsTests(
     __dirname,
     'scenario-message-truncation.mjs',
-    'instrument-with-pii.mjs',
+    'instrument-with-truncation.mjs',
     (createRunner, test) => {
       test('truncates messages when they exceed byte limit', async () => {
         await createRunner()
diff --git a/dev-packages/node-integration-tests/suites/tracing/langchain/v1/instrument-with-truncation.mjs b/dev-packages/node-integration-tests/suites/tracing/langchain/v1/instrument-with-truncation.mjs
new file mode 100644
index 000000000000..fd4ea4c13751
--- /dev/null
+++ b/dev-packages/node-integration-tests/suites/tracing/langchain/v1/instrument-with-truncation.mjs
@@ -0,0 +1,19 @@
+import * as Sentry from '@sentry/node';
+import { loggingTransport } from '@sentry-internal/node-integration-tests';
+
+Sentry.init({
+  dsn: 'https://public@dsn.ingest.sentry.io/1337',
+  release: '1.0',
+  tracesSampleRate: 1.0,
+  dataCollection: { genAI: { inputs: true, outputs: true } },
+  transport: loggingTransport,
+  integrations: [Sentry.langChainIntegration({ enableTruncation: true })],
+  beforeSendTransaction: event => {
+    // Filter out mock express server transactions
+    if (event.transaction.includes('/v1/messages') || event.transaction.includes('/v1/chat/completions')) {
+      return null;
+    }
+    return event;
+  },
+  streamGenAiSpans: true,
+});
diff --git a/dev-packages/node-integration-tests/suites/tracing/langchain/v1/test.ts b/dev-packages/node-integration-tests/suites/tracing/langchain/v1/test.ts
index 15bd37a3cccb..26f0f14cecb1 100644
--- a/dev-packages/node-integration-tests/suites/tracing/langchain/v1/test.ts
+++ b/dev-packages/node-integration-tests/suites/tracing/langchain/v1/test.ts
@@ -216,7 +216,7 @@ conditionalTest({ min: 20 })('LangChain integration (v1)', () => {
   createEsmAndCjsTests(
     __dirname,
     'scenario-message-truncation.mjs',
-    'instrument-with-pii.mjs',
+    'instrument-with-truncation.mjs',
     (createRunner, test) => {
       test('truncates messages when they exceed byte limit', async () => {
         await createRunner()
diff --git a/dev-packages/node-integration-tests/suites/tracing/openai/instrument-with-truncation.mjs b/dev-packages/node-integration-tests/suites/tracing/openai/instrument-with-truncation.mjs
new file mode 100644
index 000000000000..abb1e1efdc28
--- /dev/null
+++ b/dev-packages/node-integration-tests/suites/tracing/openai/instrument-with-truncation.mjs
@@ -0,0 +1,18 @@
+import * as Sentry from '@sentry/node';
+import { loggingTransport } from '@sentry-internal/node-integration-tests';
+
+Sentry.init({
+  dsn: 'https://public@dsn.ingest.sentry.io/1337',
+  release: '1.0',
+  tracesSampleRate: 1.0,
+  dataCollection: { genAI: { inputs: true, outputs: true } },
+  transport: loggingTransport,
+  integrations: [Sentry.openAIIntegration({ enableTruncation: true })],
+  beforeSendTransaction: event => {
+    if (event.transaction.includes('/openai/')) {
+      return null;
+    }
+    return event;
+  },
+  streamGenAiSpans: true,
+});
diff --git a/dev-packages/node-integration-tests/suites/tracing/openai/test.ts b/dev-packages/node-integration-tests/suites/tracing/openai/test.ts
index 6f716faefe5d..ad9811a37c5f 100644
--- a/dev-packages/node-integration-tests/suites/tracing/openai/test.ts
+++ b/dev-packages/node-integration-tests/suites/tracing/openai/test.ts
@@ -1174,7 +1174,7 @@ describe('OpenAI integration', () => {
   createEsmAndCjsTests(
     __dirname,
     'truncation/scenario-message-truncation-completions.mjs',
-    'instrument-with-pii.mjs',
+    'instrument-with-truncation.mjs',
     (createRunner, test) => {
       test('truncates messages when they exceed byte limit - keeps only last message and crops it', async () => {
         await createRunner()
@@ -1278,7 +1278,7 @@ describe('OpenAI integration', () => {
   createEsmAndCjsTests(
     __dirname,
     'truncation/scenario-message-truncation-responses.mjs',
-    'instrument-with-pii.mjs',
+    'instrument-with-truncation.mjs',
     (createRunner, test) => {
       test('truncates string inputs when they exceed byte limit', async () => {
         await createRunner()
@@ -1603,7 +1603,7 @@ describe('OpenAI integration', () => {
     });
   });
 
-  createEsmAndCjsTests(__dirname, 'scenario-vision.mjs', 'instrument-with-pii.mjs', (createRunner, test) => {
+  createEsmAndCjsTests(__dirname, 'scenario-vision.mjs', 'instrument-with-truncation.mjs', (createRunner, test) => {
     test('redacts inline base64 image data in vision requests', async () => {
       await createRunner()
         .ignore('event')
diff --git a/dev-packages/node-integration-tests/suites/tracing/openai/truncation/scenario-message-truncation-completions.mjs b/dev-packages/node-integration-tests/suites/tracing/openai/truncation/scenario-message-truncation-completions.mjs
index 7b0cdd730aa3..f443ab3a47fe 100644
--- a/dev-packages/node-integration-tests/suites/tracing/openai/truncation/scenario-message-truncation-completions.mjs
+++ b/dev-packages/node-integration-tests/suites/tracing/openai/truncation/scenario-message-truncation-completions.mjs
@@ -45,7 +45,7 @@ async function run() {
       apiKey: 'mock-api-key',
     });
 
-    const client = instrumentOpenAiClient(mockClient);
+    const client = instrumentOpenAiClient(mockClient, { enableTruncation: true, recordInputs: true });
 
     // Test 1: Given an array of messages only the last message should be kept
     // The last message should be truncated to fit within the 20KB limit
diff --git a/dev-packages/node-integration-tests/suites/tracing/openai/truncation/scenario-message-truncation-responses.mjs b/dev-packages/node-integration-tests/suites/tracing/openai/truncation/scenario-message-truncation-responses.mjs
index aebd3341eb33..692f5fd87ca7 100644
--- a/dev-packages/node-integration-tests/suites/tracing/openai/truncation/scenario-message-truncation-responses.mjs
+++ b/dev-packages/node-integration-tests/suites/tracing/openai/truncation/scenario-message-truncation-responses.mjs
@@ -77,7 +77,7 @@ async function run() {
       apiKey: 'mock-api-key',
     });
 
-    const client = instrumentOpenAiClient(mockClient);
+    const client = instrumentOpenAiClient(mockClient, { enableTruncation: true, recordInputs: true });
 
     // Create 1 large message that gets truncated to fit within the 20KB limit
     const largeContent = 'A'.repeat(25000) + 'B'.repeat(25000); // ~50KB gets truncated to include only As
diff --git a/dev-packages/node-integration-tests/suites/tracing/vercelai/instrument-with-truncation.mjs b/dev-packages/node-integration-tests/suites/tracing/vercelai/instrument-with-truncation.mjs
new file mode 100644
index 000000000000..7afab89bece4
--- /dev/null
+++ b/dev-packages/node-integration-tests/suites/tracing/vercelai/instrument-with-truncation.mjs
@@ -0,0 +1,12 @@
+import * as Sentry from '@sentry/node';
+import { loggingTransport } from '@sentry-internal/node-integration-tests';
+
+Sentry.init({
+  dsn: 'https://public@dsn.ingest.sentry.io/1337',
+  release: '1.0',
+  tracesSampleRate: 1.0,
+  dataCollection: { genAI: { inputs: true, outputs: true } },
+  transport: loggingTransport,
+  integrations: [Sentry.vercelAIIntegration({ enableTruncation: true })],
+  streamGenAiSpans: true,
+});
diff --git a/dev-packages/node-integration-tests/suites/tracing/vercelai/test.ts b/dev-packages/node-integration-tests/suites/tracing/vercelai/test.ts
index 1372a54cdeb1..350207b16af0 100644
--- a/dev-packages/node-integration-tests/suites/tracing/vercelai/test.ts
+++ b/dev-packages/node-integration-tests/suites/tracing/vercelai/test.ts
@@ -446,7 +446,7 @@ describe('Vercel AI integration', () => {
   createEsmAndCjsTests(
     __dirname,
     'scenario-message-truncation.mjs',
-    'instrument-with-pii.mjs',
+    'instrument-with-truncation.mjs',
     (createRunner, test) => {
       test('truncates messages when they exceed byte limit', async () => {
         await createRunner()
diff --git a/packages/core/src/tracing/ai/utils.ts b/packages/core/src/tracing/ai/utils.ts
index 2c152b3fd8f2..82ac952e4b9a 100644
--- a/packages/core/src/tracing/ai/utils.ts
+++ b/packages/core/src/tracing/ai/utils.ts
@@ -60,11 +60,22 @@ export function resolveAIRecordingOptions<T extends AIRecordingOptions>(options?
 /**
  * Resolves whether truncation should be enabled.
  * If the user explicitly set `enableTruncation`, that value is used.
- * Otherwise, truncation is disabled when span streaming is active.
+ * Otherwise, truncation is disabled whenever gen_ai spans are sent through the span streaming / v2
+ * span path, i.e. full span streaming (`traceLifecycle: 'stream'`) or `streamGenAiSpans`. That path
+ * is not subject to the transaction payload-size limits that truncation works around, so the full
+ * message data can be retained.
  */
 export function shouldEnableTruncation(enableTruncation: boolean | undefined): boolean {
+  if (enableTruncation !== undefined) {
+    return enableTruncation;
+  }
+
   const client = getClient();
-  return enableTruncation ?? !(client && hasSpanStreamingEnabled(client));
+  if (!client) {
+    return true;
+  }
+
+  return !hasSpanStreamingEnabled(client) && !client.getOptions().streamGenAiSpans;
 }
 
 /**
diff --git a/packages/core/src/types/options.ts b/packages/core/src/types/options.ts
index a6029ee86e2f..f40a79c04ecf 100644
--- a/packages/core/src/types/options.ts
+++ b/packages/core/src/types/options.ts
@@ -569,6 +569,11 @@ export interface ClientOptions<TO extends BaseTransportOptions = BaseTransportOp
    *
    * This enables streaming gen_ai spans, avoiding payload size limits of usual transactions.
    *
+   * Because the v2 span format is not subject to the transaction payload-size limits that gen_ai message
+   * truncation exists to work around, enabling this option also disables gen_ai input truncation (and the
+   * inline-media redaction that rides along with it) by default. Set `enableTruncation: true` on the
+   * respective AI integration to opt back into truncation.
+   *
    * @default false
    */
   streamGenAiSpans?: boolean;
diff --git a/packages/core/test/lib/tracing/ai/utils.test.ts b/packages/core/test/lib/tracing/ai/utils.test.ts
index c310bd4a0475..cc3bcec3cf31 100644
--- a/packages/core/test/lib/tracing/ai/utils.test.ts
+++ b/packages/core/test/lib/tracing/ai/utils.test.ts
@@ -1,6 +1,10 @@
 import { afterEach, beforeEach, describe, expect, it } from 'vitest';
 import { getCurrentScope, getGlobalScope, getIsolationScope, setCurrentClient } from '../../../../src';
-import { resolveAIRecordingOptions, wrapPromiseWithMethods } from '../../../../src/tracing/ai/utils';
+import {
+  resolveAIRecordingOptions,
+  shouldEnableTruncation,
+  wrapPromiseWithMethods,
+} from '../../../../src/tracing/ai/utils';
 import { getDefaultTestClientOptions, TestClient } from '../../../mocks/client';
 
 describe('resolveAIRecordingOptions', () => {
@@ -83,6 +87,55 @@ describe('resolveAIRecordingOptions', () => {
   });
 });
 
+describe('shouldEnableTruncation', () => {
+  beforeEach(() => {
+    getCurrentScope().clear();
+    getIsolationScope().clear();
+    getGlobalScope().clear();
+  });
+
+  afterEach(() => {
+    getCurrentScope().clear();
+    getIsolationScope().clear();
+    getGlobalScope().clear();
+  });
+
+  function setupClient(options: Parameters<typeof getDefaultTestClientOptions>[0] = {}): void {
+    const client = new TestClient(getDefaultTestClientOptions({ tracesSampleRate: 1, ...options }));
+    setCurrentClient(client);
+    client.init();
+  }
+
+  it('defaults to true when no client is set', () => {
+    expect(shouldEnableTruncation(undefined)).toBe(true);
+  });
+
+  it('defaults to true with a default client (no streaming)', () => {
+    setupClient();
+    expect(shouldEnableTruncation(undefined)).toBe(true);
+  });
+
+  it('defaults to false when streamGenAiSpans is enabled', () => {
+    setupClient({ streamGenAiSpans: true });
+    expect(shouldEnableTruncation(undefined)).toBe(false);
+  });
+
+  it('defaults to false when span streaming is enabled (traceLifecycle: stream)', () => {
+    setupClient({ traceLifecycle: 'stream' });
+    expect(shouldEnableTruncation(undefined)).toBe(false);
+  });
+
+  it('explicit enableTruncation: true overrides streamGenAiSpans', () => {
+    setupClient({ streamGenAiSpans: true });
+    expect(shouldEnableTruncation(true)).toBe(true);
+  });
+
+  it('explicit enableTruncation: false overrides the default', () => {
+    setupClient();
+    expect(shouldEnableTruncation(false)).toBe(false);
+  });
+});
+
 describe('wrapPromiseWithMethods', () => {
   /**
    * Creates a mock APIPromise that mimics the behavior of OpenAI/Anthropic SDK APIPromise.