diff --git a/packages/core/src/__tests__/llm-connections.test.ts b/packages/core/src/__tests__/llm-connections.test.ts
index 1674479ed8..a258cb84e1 100644
--- a/packages/core/src/__tests__/llm-connections.test.ts
+++ b/packages/core/src/__tests__/llm-connections.test.ts
@@ -301,3 +301,30 @@ test('a quarantined model id is vetoed even when enabled and present in the inve
     id: 'nemotron-3-ultra-free',
   });
 });
+
+test('a quarantined stored default is dropped from the picker, not re-added as a missing-default row', () => {
+  // The retired `x-preview-f-free` was picker-visible before the quarantine, so
+  // an upgrade connection can carry it as `defaultModel` and enabled. `models`
+  // and `enabledModelIds` are filtered against `brokenModelIds`, but the raw
+  // `defaultModel` used to pass through unfiltered and `makeMissingDefaultEntry`
+  // re-added it as a selectable `provider_default` row — visible and pickable
+  // while `authorizeConnectionModel` vetoed the same id. The picker and the send
+  // authority must agree: neither offers it, and the live model still renders.
+  const connection = {
+    connectionId: 'connection-opencode-free',
+    slug: 'opencode-free',
+    name: 'OpenCode Free',
+    providerType: 'opencode-free' as ProviderType,
+    enabled: true,
+    defaultModel: 'x-preview-f-free',
+    enabledModelIds: ['x-preview-f-free', 'nemotron-3-ultra-free'],
+    models: [{ id: 'x-preview-f-free' }, { id: 'nemotron-3-ultra-free' }],
+    modelSource: 'fetched' as const,
+    createdAt: 1,
+    updatedAt: 1,
+  };
+  const models = buildChatModelChoices([connection]).map(({ model }) => model);
+  assert.ok(!models.includes('x-preview-f-free'), 'quarantined default must not be offered');
+  assert.ok(models.includes('nemotron-3-ultra-free'), 'live enabled model still renders');
+  assert.equal(authorizeConnectionModel(connection, 'x-preview-f-free'), undefined);
+});
diff --git a/packages/core/src/__tests__/provider-catalog-contract.test.ts b/packages/core/src/__tests__/provider-catalog-contract.test.ts
index ef03f43fa2..2db51dde6a 100644
--- a/packages/core/src/__tests__/provider-catalog-contract.test.ts
+++ b/packages/core/src/__tests__/provider-catalog-contract.test.ts
@@ -213,3 +213,32 @@ describe('provider catalog contract — fallback lifecycle', () => {
     assert.deepEqual(regressed, []);
   });
 });
+
+describe('opencode-free retired-model quarantine', () => {
+  const opencodeFree = PROVIDER_REGISTRY['opencode-free'];
+
+  // Ox Alpha Free (x-preview-f-free) was retired upstream on OpenCode Zen while
+  // models.dev still snapshots it free+active, so the derivation would keep
+  // offering it as a default-enabled, picker-visible row. Remove this assertion
+  // together with the OPENCODE_FREE_BROKEN_MODEL_IDS entry once the snapshot
+  // marks it deprecated (or upstream serves it again).
+  it('quarantines x-preview-f-free out of the offered free models', () => {
+    assert.ok(opencodeFree.brokenModelIds?.includes('x-preview-f-free'));
+    assert.ok(!(opencodeFree.fallbackModels ?? []).includes('x-preview-f-free'));
+    assert.ok(!(opencodeFree.defaultEnabledModelIds ?? []).includes('x-preview-f-free'));
+  });
+
+  // Mechanism guard, independent of which ids the deny-list holds: a quarantined
+  // id must never leak back into the offered candidates through either path.
+  it('never offers a quarantined broken id as a free candidate', () => {
+    const broken = new Set(opencodeFree.brokenModelIds ?? []);
+    const offered = [
+      ...(opencodeFree.fallbackModels ?? []),
+      ...(opencodeFree.defaultEnabledModelIds ?? []),
+    ];
+    assert.deepEqual(
+      offered.filter((id) => broken.has(id)),
+      [],
+    );
+  });
+});
diff --git a/packages/core/src/model-catalog.ts b/packages/core/src/model-catalog.ts
index 72a56c67a4..ed2a5c7751 100644
--- a/packages/core/src/model-catalog.ts
+++ b/packages/core/src/model-catalog.ts
@@ -264,10 +264,21 @@ export function buildConnectionModelCatalogEntries(
   const fallbackModels = [...(catalogFallbackModels ?? defaults.fallbackModels)].filter(
     (id) => !broken.has(id),
   );
+  // A quarantined id persisted as this connection's `defaultModel` must not
+  // re-enter the catalog either. `models` and `enabledModelIds` are filtered
+  // below, but a broken default reaches `makeMissingDefaultEntry` unfiltered and
+  // would be re-added as a selectable `provider_default` row — picker-visible
+  // and default-capable while `authorizeConnectionModel` vetoes the same id. A
+  // reachable persisted state: the id was picker-visible before the quarantine.
+  // Dropping it leaves the connection with no valid default (readiness reports
+  // `missing_model`), which is what a model that can no longer send warrants.
+  const defaultModel = broken.has((connection.defaultModel ?? '').trim())
+    ? undefined
+    : connection.defaultModel;
   return buildModelCatalogEntries({
     providerType: connection.providerType,
     connectionSlug: connection.slug,
-    defaultModel: connection.defaultModel,
+    defaultModel,
     models: connection.models?.filter(({ id }) => !broken.has(id)),
     modelSource: connection.modelSource,
     modelsFetchedAt: connection.modelsFetchedAt,
diff --git a/packages/core/src/provider-registry.ts b/packages/core/src/provider-registry.ts
index 36c3c44d0a..b14019357b 100644
--- a/packages/core/src/provider-registry.ts
+++ b/packages/core/src/provider-registry.ts
@@ -673,7 +673,16 @@ const opencodeGoModelIds = toolCallingModelIds(
 // probes, max_tokens 8–200) — a failure shape that even "the send settles it"
 // cannot surface, which is why these ids are also vetoed in
 // `authorizeConnectionModel` rather than merely dropped from this derivation.
-const OPENCODE_FREE_BROKEN_MODEL_IDS = new Set(['muse-spark-1.2-contributor-free']);
+// 2026-08-30 x-preview-f-free (Ox Alpha Free): retired upstream — dropped from
+// the anonymous /models listing and every completion returns HTTP 401
+// {"type":"ModelError","message":"Model x-preview-f-free is not supported"}.
+// models.dev still snapshots it as free+active, so the derivation kept offering
+// it as a default-enabled, picker-visible row until this quarantine. Remove
+// once the snapshot marks it deprecated (or upstream serves it again).
+const OPENCODE_FREE_BROKEN_MODEL_IDS = new Set([
+  'muse-spark-1.2-contributor-free',
+  'x-preview-f-free',
+]);
 const opencodeFreeModelIds = toolCallingModelIds(
   'OpenCode Free',
   Object.fromEntries(