diff --git a/changelog.d/fixes/12800-cliproxyapi-unknown-provider.md b/changelog.d/fixes/12800-cliproxyapi-unknown-provider.md
new file mode 100644
index 0000000000..cc0a6e2f21
--- /dev/null
+++ b/changelog.d/fixes/12800-cliproxyapi-unknown-provider.md
@@ -0,0 +1 @@
+- fix(routing): recognize CLIProxyAPI's 'unknown provider for model' 400 as fallback-worthy (#12800)
diff --git a/open-sse/services/accountFallback.ts b/open-sse/services/accountFallback.ts
index 1d9e79cbb1..5d947d429a 100644
--- a/open-sse/services/accountFallback.ts
+++ b/open-sse/services/accountFallback.ts
@@ -376,7 +376,7 @@ export const MODEL_ACCESS_DENIED_PATTERNS = [
   /\bunsupported\s+model\b/i,
   /\baccess.*denied.*model\b/i,
   /\bmodel.*access.*denied\b/i,
-  /\bplease select a different model\b/i,
+  /\bplease select a different model\b/i, /\bunknown\s+provider\s+for\s+model\b/i,
   // "...access to the requested model" / "model ... access" — bounded lookahead
   // (no nested quantifiers) so it stays ReDoS-safe while requiring BOTH an
   // access/permission word and "model" so a pure auth error never matches.
@@ -416,7 +416,7 @@ const PROVIDER_MODEL_UNSUPPORTED_PATTERNS = [
   /\bmodel\b[\s\S]{0,80}?\b(?:does\s+not\s+support|doesn't\s+support|unsupported)\b/i,
   /\b(?:does\s+not\s+support|doesn't\s+support|unsupported)\b[\s\S]{0,80}?\bmodel\b/i,
   /\bunsupported\s+model\b/i,
-  /\bplease select a different model\b/i,
+  /\bplease select a different model\b/i, /\bunknown\s+provider\s+for\s+model\b/i,
 ];
 
 /**
diff --git a/tests/unit/cliproxyapi-unknown-provider-400-12800.test.ts b/tests/unit/cliproxyapi-unknown-provider-400-12800.test.ts
new file mode 100644
index 0000000000..f0871e581b
--- /dev/null
+++ b/tests/unit/cliproxyapi-unknown-provider-400-12800.test.ts
@@ -0,0 +1,26 @@
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+
+import {
+  MODEL_ACCESS_DENIED_PATTERNS,
+  isProviderModelUnsupported400,
+} from "../../open-sse/services/accountFallback.ts";
+
+const CLIPROXYAPI_ERROR_TEXT = "unknown provider for model Qwen/Qwen3.6-27B-TEE";
+
+describe("#12800 — CLIProxyAPI 'unknown provider for model X' classification", () => {
+  it("MODEL_ACCESS_DENIED_PATTERNS should recognize it as a model-access-denied 400", () => {
+    const matches = MODEL_ACCESS_DENIED_PATTERNS.some((p) => p.test(CLIPROXYAPI_ERROR_TEXT));
+    assert.equal(matches, true);
+  });
+
+  it("isProviderModelUnsupported400() should recognize it as provider-wide unsupported", () => {
+    const result = isProviderModelUnsupported400(400, CLIPROXYAPI_ERROR_TEXT);
+    assert.equal(result, true);
+  });
+
+  it("should not match a genuine auth/credential error", () => {
+    const authText = "invalid api key for model Qwen/Qwen3.6-27B-TEE";
+    assert.equal(isProviderModelUnsupported400(400, authText), false);
+  });
+});