diff --git a/packages/core/src/utils/openaiLogger.test.ts b/packages/core/src/utils/openaiLogger.test.ts
index b93f5c73028..283ac44b7cb 100644
--- a/packages/core/src/utils/openaiLogger.test.ts
+++ b/packages/core/src/utils/openaiLogger.test.ts
@@ -195,6 +195,52 @@ describe('OpenAILogger', () => {
       );
     });
 
+    it('should include a subagent suffix without the session id', async () => {
+      const logger = new OpenAILogger(testTempDir);
+      await logger.initialize();
+
+      const request = {
+        model: 'claude-opus-4-7',
+        messages: [{ role: 'user', content: 'test' }],
+      };
+      const response = { id: 'test-id', choices: [] };
+
+      const logPath = await logger.logInteraction(
+        request,
+        response,
+        undefined,
+        'e097d32b-82d6-422a-afa6-f6184565a8ab#Explore-g2tss0#7',
+      );
+
+      const basename = path.basename(logPath);
+      expect(basename).toMatch(
+        /openai-\d{4}-\d{2}-\d{2}T\d{2}-\d{2}-\d{2}\.\d{3}Z-[a-f0-9]{8}-subagent-Explore-g2tss0\.json/,
+      );
+      expect(basename).not.toContain('e097d32b');
+    });
+
+    it('should not include a suffix for main-session prompt ids', async () => {
+      const logger = new OpenAILogger(testTempDir);
+      await logger.initialize();
+
+      const request = {
+        model: 'claude-opus-4-7',
+        messages: [{ role: 'user', content: 'test' }],
+      };
+      const response = { id: 'test-id', choices: [] };
+
+      const logPath = await logger.logInteraction(
+        request,
+        response,
+        undefined,
+        'e097d32b-82d6-422a-afa6-f6184565a8ab########0',
+      );
+
+      expect(path.basename(logPath)).toMatch(
+        /openai-\d{4}-\d{2}-\d{2}T\d{2}-\d{2}-\d{2}\.\d{3}Z-[a-f0-9]{8}\.json/,
+      );
+    });
+
     it('should write correct log data structure', async () => {
       const logger = new OpenAILogger(testTempDir);
       await logger.initialize();
diff --git a/packages/core/src/utils/openaiLogger.ts b/packages/core/src/utils/openaiLogger.ts
index 374a2d343a4..0807292427d 100644
--- a/packages/core/src/utils/openaiLogger.ts
+++ b/packages/core/src/utils/openaiLogger.ts
@@ -13,16 +13,38 @@ import { isInternalPromptId } from './internalPromptIds.js';
 
 const debugLogger = createDebugLogger('OPENAI_LOGGER');
 
-function sanitizePromptIdForFilename(
-  promptId: string | undefined,
+function sanitizeDiagnosticSuffix(
+  suffix: string | undefined,
 ): string | undefined {
-  if (!promptId || !isInternalPromptId(promptId)) return undefined;
-  const sanitized = promptId
+  if (!suffix) return undefined;
+  const sanitized = suffix
     .replace(/[^a-zA-Z0-9._-]+/g, '-')
     .replace(/^-+|-+$/g, '');
   return sanitized || undefined;
 }
 
+function extractSubagentSuffix(promptId: string): string | undefined {
+  const parts = promptId.split('#');
+  if (parts.length !== 3) return undefined;
+
+  const [, subagentId, turn] = parts;
+  if (!subagentId || !turn || !/^\d+$/.test(turn)) {
+    return undefined;
+  }
+
+  return `subagent-${subagentId}`;
+}
+
+function promptIdSuffixForFilename(
+  promptId: string | undefined,
+): string | undefined {
+  if (!promptId) return undefined;
+  if (isInternalPromptId(promptId)) {
+    return sanitizeDiagnosticSuffix(promptId);
+  }
+  return sanitizeDiagnosticSuffix(extractSubagentSuffix(promptId));
+}
+
 /**
  * Logger specifically for OpenAI API requests and responses
  */
@@ -75,8 +97,8 @@ export class OpenAILogger {
    * @param request The request sent to OpenAI
    * @param response The response received from OpenAI
    * @param error Optional error if the request failed
-   * @param promptId Optional prompt id; internal prompt ids are appended to
-   *                 the filename after timestamp and id.
+   * @param promptId Optional prompt id; internal and subagent prompt ids are
+   *                 appended to the filename after timestamp and id.
    * @returns The file path where the log was written
    */
   async logInteraction(
@@ -91,7 +113,7 @@ export class OpenAILogger {
 
     const timestamp = new Date().toISOString().replace(/:/g, '-');
     const id = uuidv4().slice(0, 8);
-    const promptIdSuffix = sanitizePromptIdForFilename(promptId);
+    const promptIdSuffix = promptIdSuffixForFilename(promptId);
     const filename = promptIdSuffix
       ? `openai-${timestamp}-${id}-${promptIdSuffix}.json`
       : `openai-${timestamp}-${id}.json`;