diff --git a/src/adapters/cursor/discovery.ts b/src/adapters/cursor/discovery.ts
index dd77472723..718323b6a2 100644
--- a/src/adapters/cursor/discovery.ts
+++ b/src/adapters/cursor/discovery.ts
@@ -214,10 +214,23 @@ export function filterCursorConfiguredModelsByLiveDiscovery<T extends { id: stri
   liveIds: readonly string[],
 ): T[] {
   return configured.filter(model =>
-    isCursorRouterModelId(model.id) || isCursorModelAvailableForAccount(model.id, liveIds),
+    !CURSOR_KNOWN_UNCALLABLE_MODEL_IDS.has(model.id)
+    && (isCursorRouterModelId(model.id) || isCursorModelAvailableForAccount(model.id, liveIds)),
   );
 }
 
+/**
+ * Models GetUsableModels advertises but whose every Run returns not_found (catalog honesty,
+ * devlog 260826_cursor_responses_gap 060). Live probes 2026-08-26: cursor/claude-opus-5 failed
+ * 100% ("Cursor Connect error not_found") while its -fast and -thinking siblings — separate
+ * wire families — succeed. Quarantined here, in the shared filter, so live, cached, stale, and
+ * static serving paths all agree. Custom user provider overrides are not routed through this
+ * canonical seed and stay untouched.
+ */
+export const CURSOR_KNOWN_UNCALLABLE_MODEL_IDS: ReadonlySet<string> = new Set([
+  "claude-opus-5",
+]);
+
 export const CURSOR_STATIC_MODELS: readonly CursorModelInfo[] = normalizeCursorModels([
   // Context windows and the model lineup mirror Cursor's public models/pricing docs plus the jawcode
   // SOT (../jawcode/packages/ai/src/models.json, `cursor` provider), which mirrors the real
@@ -245,7 +258,8 @@ export const CURSOR_STATIC_MODELS: readonly CursorModelInfo[] = normalizeCursorM
   { id: "claude-opus-4-7-fast", contextWindow: CONTEXT_200K, supportsReasoningEffort: true },
   { id: "claude-opus-4-8-fast", contextWindow: CONTEXT_200K, supportsReasoningEffort: true },
   { id: "claude-opus-4-8", contextWindow: CONTEXT_200K, supportsReasoningEffort: true },
-  { id: "claude-opus-5", contextWindow: CONTEXT_200K, supportsReasoningEffort: true },
+  // claude-opus-5 (bare) removed from the seed: GetUsableModels lists it but every Run returns
+  // not_found (quarantined via CURSOR_KNOWN_UNCALLABLE_MODEL_IDS; -fast/-thinking families stay).
   { id: "claude-opus-5-fast", contextWindow: CONTEXT_200K, supportsReasoningEffort: true },
   { id: "claude-fable-5", contextWindow: CONTEXT_200K, supportsReasoningEffort: true },
 
diff --git a/tests/cursor-uncallable-quarantine.test.ts b/tests/cursor-uncallable-quarantine.test.ts
new file mode 100644
index 0000000000..99bc3957a0
--- /dev/null
+++ b/tests/cursor-uncallable-quarantine.test.ts
@@ -0,0 +1,33 @@
+import { describe, expect, test } from "bun:test";
+import {
+  CURSOR_KNOWN_UNCALLABLE_MODEL_IDS,
+  CURSOR_STATIC_MODELS,
+  filterCursorConfiguredModelsByLiveDiscovery,
+} from "../src/adapters/cursor/discovery";
+
+describe("cursor uncallable-model quarantine (devlog 260826 060)", () => {
+  test("static seed no longer carries bare claude-opus-5", () => {
+    expect(CURSOR_STATIC_MODELS.some(model => model.id === "claude-opus-5")).toBe(false);
+  });
+
+  test("siblings from other wire families survive", () => {
+    expect(CURSOR_STATIC_MODELS.some(model => model.id === "claude-opus-5-fast")).toBe(true);
+  });
+
+  test("live filter drops quarantined ids even when GetUsableModels lists them", () => {
+    const configured = [{ id: "claude-opus-5" }, { id: "claude-opus-5-fast" }, { id: "grok-4.6" }];
+    const live = ["claude-opus-5-high", "claude-opus-5-high-fast", "grok-4.6-high"];
+    const filtered = filterCursorConfiguredModelsByLiveDiscovery(configured, live);
+    expect(filtered.map(model => model.id)).toEqual(["claude-opus-5-fast", "grok-4.6"]);
+  });
+
+  test("quarantine applies with an empty live list too (stale/static degradation path)", () => {
+    const configured = [{ id: "claude-opus-5" }, { id: "auto" }];
+    const filtered = filterCursorConfiguredModelsByLiveDiscovery(configured, []);
+    expect(filtered.some(model => model.id === "claude-opus-5")).toBe(false);
+  });
+
+  test("quarantine set stays narrow", () => {
+    expect([...CURSOR_KNOWN_UNCALLABLE_MODEL_IDS]).toEqual(["claude-opus-5"]);
+  });
+});