feat(ui): run the Anthropic Family preset's reasoning tier on Opus 5 at high thinking (#38490)

The preset put Fable 5 in REASONING, sitting above Opus in a Haiku to Sonnet to
Opus ladder even though Fable is the lighter model. Run Opus 5 there instead, at
high thinking, so the tier above COMPLEX is the same model thinking harder rather
than a different and lighter one.

This is the first bundled preset to carry tier_model_configs. The round trip was
already built and unit tested, but nothing between the bundled JSON and the
create payload asserted on it, so add that coverage here.

ui/litellm-dashboard/src/autorouter_presets.json

@@ -1,13 +1,16 @@
 {
   "anthropic_family": {
     "label": "Anthropic Family",
-    "description": "Routes across the Claude model family: Haiku for simple queries, Sonnet for medium, Opus for complex and reasoning-heavy requests.",
+    "description": "Routes across the Claude model family: Haiku for simple queries, Sonnet for medium, Opus for complex, Opus at high thinking for reasoning.",
     "complexity_router_config": {
       "tiers": {
         "SIMPLE": ["claude-haiku-4-5"],
         "MEDIUM": ["claude-sonnet-5"],
         "COMPLEX": ["claude-opus-5"],
-        "REASONING": ["claude-fable-5"]
+        "REASONING": ["claude-opus-5"]
+      },
+      "tier_model_configs": {
+        "REASONING": [{ "model_name": "claude-opus-5", "litellm_params": { "reasoning_effort": "high" } }]
       },
       "classifier_type": "heuristic",
       "escalation_keywords": ["LITELLM ESCALATE"],

ui/litellm-dashboard/src/components/add_model/add_auto_router_tab.test.tsx

@@ -592,6 +592,28 @@ describe("AddAutoRouterTab", () => {
       });
     });
 
+    // Every step between the bundled JSON and the payload drops these params silently.
+    it("carries a preset's per-tier reasoning effort through to the create payload", async () => {
+      const user = userEvent.setup();
+      mockFetchAvailableModels.mockResolvedValue(ALL_FAMILY_MODELS);
+
+      renderWithProviders(<Harness />);
+      await waitForPresetEnabled("Anthropic Family");
+      await selectTemplate("Anthropic Family");
+
+      await user.type(screen.getByPlaceholderText(/smart_router/i), "anthropic-router");
+      await user.click(screen.getByRole("button", { name: /add auto router/i }));
+
+      await waitFor(() => expect(handleAddAutoRouterSubmit).toHaveBeenCalled());
+      expect(vi.mocked(handleAddAutoRouterSubmit).mock.calls.at(-1)?.[0]).toMatchObject({
+        complexity_router_config: {
+          tier_model_configs: {
+            REASONING: [{ model_name: "claude-opus-5", litellm_params: { reasoning_effort: "high" } }],
+          },
+        },
+      });
+    });
+
     // Bugbot-found bug: submitBlockedReason disables the button for this, but Form's onFinish
     // (wired to the same handler as the button) fires whenever the form itself is submitted,
     // independent of the button's own disabled state. Without submitRecommendedRouter re-checking

ui/litellm-dashboard/src/lib/autorouter_presets.test.ts

@@ -99,6 +99,36 @@ describe("autorouter_presets", () => {
     );
   });
 
+  // Opus serves both tiers, so the effort is all that separates them and losing it fails silently.
+  it("pins the anthropic preset's reasoning tier to Opus at high thinking", () => {
+    const config = getPresetByKey("anthropic_family")!.complexity_router_config;
+    expect(config.tiers.COMPLEX).toEqual(["claude-opus-5"]);
+    expect(config.tiers.REASONING).toEqual(["claude-opus-5"]);
+    expect(config.tier_model_configs).toEqual({
+      REASONING: [{ model_name: "claude-opus-5", litellm_params: { reasoning_effort: "high" } }],
+    });
+  });
+
+  // serializeTierModelConfigs filters on the tier's models, so a stray name drops silently.
+  it("never names a model in tier_model_configs that its own tier does not hold", () => {
+    for (const preset of getAllPresets()) {
+      const { tiers, tier_model_configs: configs } = preset.complexity_router_config;
+      for (const [tier, entries] of Object.entries(configs ?? {})) {
+        for (const entry of entries) {
+          expect(tiers[tier as keyof typeof tiers] ?? [], `${preset.key}.${tier}`).toContain(entry.model_name);
+        }
+      }
+    }
+  });
+
+  it("prefills the anthropic preset's effort through to tier_model_params", () => {
+    const preset = getPresetByKey("anthropic_family")!;
+    const prefill = buildPresetPrefill(preset.complexity_router_config, groupsOnly(getRequiredModelsInPreset(preset)));
+    expect(prefill.complexityRouterConfig.tier_model_params).toEqual({
+      REASONING: { "claude-opus-5": { reasoning_effort: "high" } },
+    });
+  });
+
   it("pins the gemini preset to concrete model ids, never Google's hot-swapping -latest aliases", () => {
     const gemini = getPresetByKey("gemini_family")!;
     const config = gemini.complexity_router_config;