diff --git a/src/agents/failover-error.test.ts b/src/agents/failover-error.test.ts
index 3bf27c21cff..4e4379bf5da 100644
--- a/src/agents/failover-error.test.ts
+++ b/src/agents/failover-error.test.ts
@@ -18,6 +18,10 @@ const GEMINI_RESOURCE_EXHAUSTED_MESSAGE =
   "RESOURCE_EXHAUSTED: Resource has been exhausted (e.g. check quota).";
 // OpenRouter 402 billing example: https://openrouter.ai/docs/api-reference/errors
 const OPENROUTER_CREDITS_MESSAGE = "Payment Required: insufficient credits";
+// Issue-backed Anthropic/OpenAI-compatible insufficient_quota payload under HTTP 400:
+// https://github.com/openclaw/openclaw/issues/23440
+const INSUFFICIENT_QUOTA_PAYLOAD =
+  '{"type":"error","error":{"type":"insufficient_quota","message":"Your account has insufficient quota balance to run this request."}}';
 // AWS Bedrock 429 ThrottlingException / 503 ServiceUnavailable:
 // https://docs.aws.amazon.com/bedrock/latest/userguide/troubleshooting-api-error-codes.html
 const BEDROCK_THROTTLING_EXCEPTION_MESSAGE =
@@ -100,6 +104,15 @@ describe("failover-error", () => {
     ).toBe("timeout");
   });
 
+  it("treats 400 insufficient_quota payloads as billing instead of format", () => {
+    expect(
+      resolveFailoverReasonFromError({
+        status: 400,
+        message: INSUFFICIENT_QUOTA_PAYLOAD,
+      }),
+    ).toBe("billing");
+  });
+
   it("infers format errors from error messages", () => {
     expect(
       resolveFailoverReasonFromError({
diff --git a/src/agents/model-fallback.test.ts b/src/agents/model-fallback.test.ts
index 2c58a42c99a..93310d51f8e 100644
--- a/src/agents/model-fallback.test.ts
+++ b/src/agents/model-fallback.test.ts
@@ -179,6 +179,10 @@ const OPENAI_RATE_LIMIT_MESSAGE =
 // Anthropic overloaded_error example shape: https://docs.anthropic.com/en/api/errors
 const ANTHROPIC_OVERLOADED_PAYLOAD =
   '{"type":"error","error":{"type":"overloaded_error","message":"Overloaded"},"request_id":"req_test"}';
+// Issue-backed Anthropic/OpenAI-compatible insufficient_quota payload under HTTP 400:
+// https://github.com/openclaw/openclaw/issues/23440
+const INSUFFICIENT_QUOTA_PAYLOAD =
+  '{"type":"error","error":{"type":"insufficient_quota","message":"Your account has insufficient quota balance to run this request."}}';
 // Internal OpenClaw compatibility marker, not a provider API contract.
 const MODEL_COOLDOWN_MESSAGE = "model_cooldown: All credentials for model gpt-5 are cooling down";
 // SDK/transport compatibility marker, not a provider API contract.
@@ -399,6 +403,25 @@ describe("runWithModelFallback", () => {
     });
   });
 
+  it("records 400 insufficient_quota payloads as billing during fallback", async () => {
+    const cfg = makeCfg();
+    const run = vi
+      .fn()
+      .mockRejectedValueOnce(Object.assign(new Error(INSUFFICIENT_QUOTA_PAYLOAD), { status: 400 }))
+      .mockResolvedValueOnce("ok");
+
+    const result = await runWithModelFallback({
+      cfg,
+      provider: "openai",
+      model: "gpt-4.1-mini",
+      run,
+    });
+
+    expect(result.result).toBe("ok");
+    expect(result.attempts).toHaveLength(1);
+    expect(result.attempts[0]?.reason).toBe("billing");
+  });
+
   it("falls back to configured primary for override credential validation errors", async () => {
     const cfg = makeCfg();
     const run = createOverrideFailureRun({
diff --git a/src/agents/pi-embedded-helpers.isbillingerrormessage.test.ts b/src/agents/pi-embedded-helpers.isbillingerrormessage.test.ts
index 1ca99e8a993..dd8a38d2814 100644
--- a/src/agents/pi-embedded-helpers.isbillingerrormessage.test.ts
+++ b/src/agents/pi-embedded-helpers.isbillingerrormessage.test.ts
@@ -28,6 +28,10 @@ const ANTHROPIC_OVERLOADED_PAYLOAD =
   '{"type":"error","error":{"type":"overloaded_error","message":"Overloaded"},"request_id":"req_test"}';
 // OpenRouter 402 billing example: https://openrouter.ai/docs/api-reference/errors
 const OPENROUTER_CREDITS_MESSAGE = "Payment Required: insufficient credits";
+// Issue-backed Anthropic/OpenAI-compatible insufficient_quota payload under HTTP 400:
+// https://github.com/openclaw/openclaw/issues/23440
+const INSUFFICIENT_QUOTA_PAYLOAD =
+  '{"type":"error","error":{"type":"insufficient_quota","message":"Your account has insufficient quota balance to run this request."}}';
 // Together AI error code examples: https://docs.together.ai/docs/error-codes
 const TOGETHER_PAYMENT_REQUIRED_MESSAGE =
   "402 Payment Required: The account associated with this API key has reached its maximum allowed monthly spending limit.";
@@ -531,6 +535,7 @@ describe("classifyFailoverReason", () => {
     ).toBe("rate_limit");
     expect(classifyFailoverReason("all credentials for model x are cooling down")).toBeNull();
     expect(classifyFailoverReason("invalid request format")).toBe("format");
+    expect(classifyFailoverReason(INSUFFICIENT_QUOTA_PAYLOAD)).toBe("billing");
     expect(classifyFailoverReason("deadline exceeded")).toBe("timeout");
     expect(classifyFailoverReason("request ended without sending any chunks")).toBe("timeout");
     expect(classifyFailoverReason("Connection error.")).toBe("timeout");
diff --git a/src/agents/pi-embedded-helpers/errors.ts b/src/agents/pi-embedded-helpers/errors.ts
index 58ad24f953a..e4944b0731c 100644
--- a/src/agents/pi-embedded-helpers/errors.ts
+++ b/src/agents/pi-embedded-helpers/errors.ts
@@ -283,6 +283,11 @@ export function classifyFailoverReasonFromHttpStatus(
     return "rate_limit";
   }
   if (status === 400) {
+    // Some providers return quota/balance errors under HTTP 400, so do not
+    // let the generic format fallback mask an explicit billing signal.
+    if (message && isBillingErrorMessage(message)) {
+      return "billing";
+    }
     return "format";
   }
   return null;
diff --git a/src/agents/pi-embedded-helpers/failover-matches.ts b/src/agents/pi-embedded-helpers/failover-matches.ts
index d1e266ff53d..abbd6e769fa 100644
--- a/src/agents/pi-embedded-helpers/failover-matches.ts
+++ b/src/agents/pi-embedded-helpers/failover-matches.ts
@@ -44,6 +44,7 @@ const ERROR_PATTERNS = {
     /["']?(?: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,
     "payment required",
     "insufficient credits",
+    /insufficient[_ ]quota/i,
     "credit balance",
     "plans & billing",
     "insufficient balance",