diff --git a/src/agents/pi-embedded-helpers.isbillingerrormessage.test.ts b/src/agents/pi-embedded-helpers.isbillingerrormessage.test.ts
index 8c0a0b1994d..13f3ea1d388 100644
--- a/src/agents/pi-embedded-helpers.isbillingerrormessage.test.ts
+++ b/src/agents/pi-embedded-helpers.isbillingerrormessage.test.ts
@@ -853,11 +853,72 @@ describe("classifyFailoverReason", () => {
     expect(classifyFailoverReason("key has been disabled")).toBe("auth_permanent");
     expect(classifyFailoverReason("account has been deactivated")).toBe("auth_permanent");
   });
-  it("classifies JSON api_error internal server failures as timeout", () => {
+  it("classifies JSON api_error with transient signal as timeout", () => {
     expect(
       classifyFailoverReason(
         '{"type":"error","error":{"type":"api_error","message":"Internal server error"}}',
       ),
     ).toBe("timeout");
+    // MiniMax non-standard message
+    expect(
+      classifyFailoverReason('{"type":"api_error","message":"unknown error, 520 (1000)"}'),
+    ).toBe("timeout");
+    // Overloaded variant
+    expect(
+      classifyFailoverReason(
+        '{"type":"error","error":{"type":"api_error","message":"Service temporarily unavailable"}}',
+      ),
+    ).toBe("timeout");
+  });
+  it("does not classify non-transient api_error payloads as timeout", () => {
+    // Context overflow - not transient
+    expect(
+      classifyFailoverReason(
+        '{"type":"error","error":{"type":"api_error","message":"Request size exceeds model context window"}}',
+      ),
+    ).not.toBe("timeout");
+    // Schema/validation error - not transient
+    expect(
+      classifyFailoverReason(
+        '{"type":"error","error":{"type":"api_error","message":"messages.1.content.1.tool_use.id should match pattern"}}',
+      ),
+    ).not.toBe("timeout");
+    // Generic unknown api_error without transient wording - should not be retried
+    expect(
+      classifyFailoverReason(
+        '{"type":"error","error":{"type":"api_error","message":"invalid input format"}}',
+      ),
+    ).not.toBe("timeout");
+  });
+  it("does not shadow billing errors that carry api_error type", () => {
+    // A provider may wrap a billing error in a JSON payload with "type":"api_error".
+    // The billing classifier must win over the broad api_error transient match.
+    expect(
+      classifyFailoverReason(
+        '{"type":"error","error":{"type":"api_error","message":"insufficient credits"}}',
+      ),
+    ).toBe("billing");
+    expect(
+      classifyFailoverReason(
+        '{"type":"error","error":{"type":"api_error","message":"Payment required"}}',
+      ),
+    ).toBe("billing");
+  });
+  it("does not shadow auth errors that carry api_error type", () => {
+    expect(
+      classifyFailoverReason(
+        '{"type":"error","error":{"type":"api_error","message":"invalid api key"}}',
+      ),
+    ).toBe("auth");
+    expect(
+      classifyFailoverReason(
+        '{"type":"error","error":{"type":"api_error","message":"unauthorized"}}',
+      ),
+    ).toBe("auth");
+    expect(
+      classifyFailoverReason(
+        '{"type":"error","error":{"type":"api_error","message":"permission_error"}}',
+      ),
+    ).toBe("auth_permanent");
   });
 });
diff --git a/src/agents/pi-embedded-helpers/errors.ts b/src/agents/pi-embedded-helpers/errors.ts
index 7719ecb41a0..3019a184fcd 100644
--- a/src/agents/pi-embedded-helpers/errors.ts
+++ b/src/agents/pi-embedded-helpers/errors.ts
@@ -670,14 +670,34 @@ export function isBillingAssistantError(msg: AssistantMessage | undefined): bool
   return isBillingErrorMessage(msg.errorMessage ?? "");
 }
 
+// Transient signal patterns for api_error payloads. Only treat an api_error as
+// retryable when the message text itself indicates a transient server issue.
+// Non-transient api_error payloads (context overflow, validation/schema errors)
+// must NOT be classified as timeout.
+const API_ERROR_TRANSIENT_SIGNALS_RE =
+  /internal server error|overload|temporarily unavailable|service unavailable|unknown error|server error|bad gateway|gateway timeout|upstream error|backend error|try again later|temporarily.+unable/i;
+
 function isJsonApiInternalServerError(raw: string): boolean {
   if (!raw) {
     return false;
   }
   const value = raw.toLowerCase();
-  // Anthropic often wraps transient 500s in JSON payloads like:
+  // Providers wrap transient 5xx errors in JSON payloads like:
   // {"type":"error","error":{"type":"api_error","message":"Internal server error"}}
-  return value.includes('"type":"api_error"') && value.includes("internal server error");
+  // Non-standard providers (e.g. MiniMax) may use different message text:
+  // {"type":"api_error","message":"unknown error, 520 (1000)"}
+  if (!value.includes('"type":"api_error"')) {
+    return false;
+  }
+  // Billing and auth errors can also carry "type":"api_error". Exclude them so
+  // the more specific classifiers further down the chain handle them correctly.
+  if (isBillingErrorMessage(raw) || isAuthErrorMessage(raw) || isAuthPermanentErrorMessage(raw)) {
+    return false;
+  }
+  // Only match when the message contains a transient signal. api_error payloads
+  // with non-transient messages (e.g. context overflow, schema validation) should
+  // fall through to more specific classifiers or remain unclassified.
+  return API_ERROR_TRANSIENT_SIGNALS_RE.test(raw);
 }
 
 export function parseImageDimensionError(raw: string): {
@@ -830,24 +850,27 @@ export function classifyFailoverReason(raw: string): FailoverReason | null {
     // Treat remaining transient 5xx provider failures as retryable transport issues.
     return "timeout";
   }
-  if (isJsonApiInternalServerError(raw)) {
-    return "timeout";
-  }
-  if (isCloudCodeAssistFormatError(raw)) {
-    return "format";
-  }
+  // Billing and auth classifiers run before the broad isJsonApiInternalServerError
+  // check so that provider errors like {"type":"api_error","message":"insufficient
+  // balance"} are correctly classified as "billing"/"auth" rather than "timeout".
   if (isBillingErrorMessage(raw)) {
     return "billing";
   }
-  if (isTimeoutErrorMessage(raw)) {
-    return "timeout";
-  }
   if (isAuthPermanentErrorMessage(raw)) {
     return "auth_permanent";
   }
   if (isAuthErrorMessage(raw)) {
     return "auth";
   }
+  if (isJsonApiInternalServerError(raw)) {
+    return "timeout";
+  }
+  if (isCloudCodeAssistFormatError(raw)) {
+    return "format";
+  }
+  if (isTimeoutErrorMessage(raw)) {
+    return "timeout";
+  }
   return null;
 }