diff --git a/src/agents/failover-error.test.ts b/src/agents/failover-error.test.ts
index ec7e7a195ee..6add16356a7 100644
--- a/src/agents/failover-error.test.ts
+++ b/src/agents/failover-error.test.ts
@@ -39,6 +39,9 @@ describe("failover-error", () => {
     expect(resolveFailoverReasonFromError({ message: "Unhandled stop reason: abort" })).toBe(
       "timeout",
     );
+    expect(resolveFailoverReasonFromError({ message: "Unhandled stop reason: error" })).toBe(
+      "timeout",
+    );
     expect(resolveFailoverReasonFromError({ message: "stop reason: abort" })).toBe("timeout");
     expect(resolveFailoverReasonFromError({ message: "reason: abort" })).toBe("timeout");
   });
diff --git a/src/agents/failover-error.ts b/src/agents/failover-error.ts
index 7b9f5194fd3..7a9d5ca354c 100644
--- a/src/agents/failover-error.ts
+++ b/src/agents/failover-error.ts
@@ -6,7 +6,7 @@ import {
 } from "./pi-embedded-helpers.js";
 
 const TIMEOUT_HINT_RE =
-  /timeout|timed out|deadline exceeded|context deadline exceeded|stop reason:\s*abort|reason:\s*abort|unhandled stop reason:\s*abort/i;
+  /timeout|timed out|deadline exceeded|context deadline exceeded|stop reason:\s*abort|reason:\s*abort|unhandled stop reason:\s*(?:abort|error)/i;
 const ABORT_TIMEOUT_RE = /request was aborted|request aborted/i;
 
 export class FailoverError extends Error {
diff --git a/src/agents/model-fallback.test.ts b/src/agents/model-fallback.test.ts
index 0b527392ef1..c40e3649eb4 100644
--- a/src/agents/model-fallback.test.ts
+++ b/src/agents/model-fallback.test.ts
@@ -743,6 +743,14 @@ describe("runWithModelFallback", () => {
     });
   });
 
+  it("falls back on unhandled stop reason error responses", async () => {
+    await expectFallsBackToHaiku({
+      provider: "openai",
+      model: "gpt-4.1-mini",
+      firstError: new Error("Unhandled stop reason: error"),
+    });
+  });
+
   it("falls back when message says aborted but error is a timeout", async () => {
     await expectFallsBackToHaiku({
       provider: "openai",
diff --git a/src/agents/pi-embedded-helpers.isbillingerrormessage.test.ts b/src/agents/pi-embedded-helpers.isbillingerrormessage.test.ts
index 21751d15dc5..0cf9df4d7f7 100644
--- a/src/agents/pi-embedded-helpers.isbillingerrormessage.test.ts
+++ b/src/agents/pi-embedded-helpers.isbillingerrormessage.test.ts
@@ -423,7 +423,12 @@ describe("isFailoverErrorMessage", () => {
   });
 
   it("matches abort stop-reason timeout variants", () => {
-    const samples = ["Unhandled stop reason: abort", "stop reason: abort", "reason: abort"];
+    const samples = [
+      "Unhandled stop reason: abort",
+      "Unhandled stop reason: error",
+      "stop reason: abort",
+      "reason: abort",
+    ];
     for (const sample of samples) {
       expect(isTimeoutErrorMessage(sample)).toBe(true);
       expect(classifyFailoverReason(sample)).toBe("timeout");
diff --git a/src/agents/pi-embedded-helpers/errors.ts b/src/agents/pi-embedded-helpers/errors.ts
index aa64450df6b..852ba227d5e 100644
--- a/src/agents/pi-embedded-helpers/errors.ts
+++ b/src/agents/pi-embedded-helpers/errors.ts
@@ -643,7 +643,7 @@ const ERROR_PATTERNS = {
     /without sending (?:any )?chunks?/i,
     /\bstop reason:\s*abort\b/i,
     /\breason:\s*abort\b/i,
-    /\bunhandled stop reason:\s*abort\b/i,
+    /\bunhandled stop reason:\s*(?:abort|error)\b/i,
   ],
   billing: [
     /["']?(?:status|code)["']?\s*[:=]\s*402\b|\bhttp\s*402\b|\berror(?:\s+code)?\s*[:=]?\s*402\b|\b(?:got|returned|received)\s+(?:a\s+)?402\b|^\s*402\s+payment/i,