diff --git a/src/codex/catalog/parsing.ts b/src/codex/catalog/parsing.ts
index 0293b4bd04..94241e8a75 100644
--- a/src/codex/catalog/parsing.ts
+++ b/src/codex/catalog/parsing.ts
@@ -406,7 +406,12 @@ export function ensureStrictCatalogFields(
   if (typeof entry.supports_reasoning_summaries !== "boolean") entry.supports_reasoning_summaries = false;
   if (typeof entry.default_reasoning_summary !== "string") entry.default_reasoning_summary = "none";
   if (typeof entry.support_verbosity !== "boolean") entry.support_verbosity = true;
-  if (typeof entry.default_verbosity !== "string") entry.default_verbosity = "low";
+  // A row that has declared it does NOT support verbosity must not also ship a default for the
+  // control it just disowned: Codex seeds its picker from `default_verbosity`, so leaving the
+  // strict-fields fallback in place re-creates the dead toggle the explicit opt-out removed.
+  // Scoped to an explicit `false`, so rows that never declare a capability keep the default.
+  if (entry.support_verbosity === false) delete entry.default_verbosity;
+  else if (typeof entry.default_verbosity !== "string") entry.default_verbosity = "low";
   if (typeof entry.apply_patch_tool_type !== "string") entry.apply_patch_tool_type = "freeform";
   if (!entry.truncation_policy || typeof entry.truncation_policy !== "object" || Array.isArray(entry.truncation_policy)) {
     entry.truncation_policy = { mode: "tokens", limit: 10000 };
diff --git a/tests/catalog-verbosity-default.test.ts b/tests/catalog-verbosity-default.test.ts
new file mode 100644
index 0000000000..75a07cca66
--- /dev/null
+++ b/tests/catalog-verbosity-default.test.ts
@@ -0,0 +1,90 @@
+import { afterEach, describe, expect, test } from "bun:test";
+import { buildCatalogEntries, gatherRoutedModels as gatherRoutedModelsDirect, upstreamNativeEntry } from "../src/codex/catalog";
+import { withStubbedProviderFetch } from "./helpers/catalog-provider-fetch";
+import { resetCatalogRuntimeStateForTests, resetOpenAiApiCatalogWarningStateForTests } from "../src/codex/catalog";
+import { clearModelCache } from "../src/codex/model-cache";
+
+const gatherRoutedModels: typeof gatherRoutedModelsDirect = (config, options) =>
+  gatherRoutedModelsDirect(withStubbedProviderFetch(config), options);
+
+afterEach(() => {
+  globalThis.fetch = originalFetch;
+  clearModelCache();
+  resetOpenAiApiCatalogWarningStateForTests();
+  resetCatalogRuntimeStateForTests();
+});
+
+const originalFetch = globalThis.fetch;
+
+/**
+ * A serialized row that declares `support_verbosity: false` must not also carry a
+ * `default_verbosity`. Codex seeds its picker from `default_verbosity`, so leaving the
+ * strict-fields fallback in place re-creates the dead toggle that the explicit opt-out
+ * (#2578 architecture) removed. All field names here are the SERIALIZED Codex spellings —
+ * `supports_verbosity` does not exist in this format, which is exactly how an earlier
+ * assertion passed while every routed row advertised the control.
+ */
+describe("catalog — default_verbosity is dropped when verbosity is unsupported", () => {
+  test("GREEN: an opted-out routed row carries no verbosity default", async () => {
+    const models = await gatherRoutedModels({
+      providers: {
+        xai: {
+          adapter: "openai-chat",
+          baseUrl: "https://api.x.ai/v1",
+          authMode: "oauth",
+          liveModels: false,
+          models: ["grok-4.6"],
+        },
+      },
+    });
+    const entries = buildCatalogEntries(null, [], models);
+    const xai = entries.find(e => e.slug === "xai/grok-4.6");
+    expect(xai?.support_verbosity).toBe(false);
+    expect(xai?.default_verbosity).toBeUndefined();
+  });
+
+  test("GREEN: a Kiro opted-out row carries no verbosity default either", async () => {
+    const models = await gatherRoutedModels({
+      providers: {
+        kiro: {
+          adapter: "kiro",
+          baseUrl: "https://runtime.us-east-1.kiro.dev",
+          authMode: "oauth",
+          liveModels: false,
+          models: ["gpt-5.6-sol"],
+        },
+      },
+    });
+    const entries = buildCatalogEntries(null, [], models);
+    const kiro = entries.find(e => e.slug === "kiro/gpt-5.6-sol");
+    expect(kiro?.support_verbosity).toBe(false);
+    expect(kiro?.default_verbosity).toBeUndefined();
+  });
+
+  test("CONTROL: rows that never declare a capability keep the permissive default", async () => {
+    const models = await gatherRoutedModels({
+      providers: {
+        plain: {
+          adapter: "openai-responses",
+          baseUrl: "https://plain.example.test/v1",
+          authMode: "key",
+          liveModels: false,
+          models: ["plain-model"],
+        },
+      },
+    });
+    const entries = buildCatalogEntries(null, [], models);
+    const plain = entries.find(e => e.slug === "plain/plain-model");
+    expect(plain?.support_verbosity).toBe(true);
+    expect(plain?.default_verbosity).toBe("low");
+  });
+
+  test("CONTROL: a native OpenAI row keeps verbosity and its default", () => {
+    const template = upstreamNativeEntry("gpt-5.6-sol");
+    expect(template).not.toBeNull();
+    const entries = buildCatalogEntries(template, ["gpt-5.6-sol"], []);
+    const native = entries.find(e => e.slug === "gpt-5.6-sol");
+    expect(native?.support_verbosity).toBe(true);
+    expect(native?.default_verbosity).toBe("low");
+  });
+});