diff --git a/ui/litellm-dashboard/src/lib/autorouter_presets.test.ts b/ui/litellm-dashboard/src/lib/autorouter_presets.test.ts
index 01c61ba6130..a2d23473fb9 100644
--- a/ui/litellm-dashboard/src/lib/autorouter_presets.test.ts
+++ b/ui/litellm-dashboard/src/lib/autorouter_presets.test.ts
@@ -11,6 +11,7 @@ import {
   buildPresetPrefill,
   buildModelAvailability,
   deploymentRefsFromModelInfo,
+  normalizeModelName,
 } from "./autorouter_presets";
 import { DEFAULT_MATCH_THRESHOLD } from "@/components/add_model/SemanticKeywordMatching";
 import { DEFAULT_ESCALATION_KEYWORDS } from "@/components/add_model/EscalationKeywords";
@@ -28,6 +29,29 @@ describe("autorouter_presets", () => {
     }
   });
 
+  // buildPresetPrefill resolves every model reference through normalizeModelName, so two spellings
+  // of the same model in one tier (e.g. "claude-sonnet-4-5" and "claude-sonnet-4.5") collapse to one
+  // key. For tier_model_configs that silently drops one model's litellm_params; catch it in the
+  // bundled data itself, since nothing else validates preset authoring.
+  it("never spells the same model two ways within a single tier", () => {
+    for (const preset of getAllPresets()) {
+      const { tiers, tier_model_configs: configs } = preset.complexity_router_config;
+      for (const tier of Object.keys(tiers) as (keyof typeof tiers)[]) {
+        const fromTierList = tiers[tier] ?? [];
+        const fromConfigs = (configs?.[tier] ?? []).map((entry) => entry.model_name);
+        const names = new Set([...fromTierList, ...fromConfigs]);
+        const byNormalized = new Map<string, string[]>();
+        for (const name of names) {
+          const key = normalizeModelName(name);
+          byNormalized.set(key, [...(byNormalized.get(key) ?? []), name]);
+        }
+        for (const spellings of byNormalized.values()) {
+          expect(new Set(spellings).size, `${preset.key}.${tier}: ${spellings.join(", ")}`).toBe(1);
+        }
+      }
+    }
+  });
+
   it("resolves a preset by its stable JSON key, not its display label", () => {
     expect(getPresetByKey("anthropic_family")?.label).toBe("Anthropic Family");
     expect(getPresetByKey("does_not_exist")).toBeUndefined();
@@ -544,5 +568,73 @@ describe("autorouter_presets", () => {
       const prefill = buildPresetPrefill(config, groupsOnly(["claude-sonnet-4.5"]));
       expect(prefill.complexityRouterConfig.tiers.SIMPLE).toEqual(["claude-sonnet-4.5"]);
     });
+
+    it("prefills the per-model litellm_params a preset carries in tier_model_configs", () => {
+      const config = {
+        tiers: { SIMPLE: ["gpt-5-nano"], MEDIUM: [], COMPLEX: [], REASONING: ["o3"] },
+        tier_model_configs: {
+          REASONING: [{ model_name: "o3", litellm_params: { reasoning_effort: "high" } }],
+        },
+        classifier_type: "heuristic" as const,
+        session_affinity: false,
+        deployment_affinity: true,
+      };
+      const prefill = buildPresetPrefill(config, groupsOnly(["gpt-5-nano", "o3"]));
+      expect(prefill.complexityRouterConfig.tier_model_params).toEqual({
+        REASONING: { o3: { reasoning_effort: "high" } },
+      });
+    });
+
+    // The params key on the preset's own spelling while the tier entry gets rewritten to the
+    // caller's. Leaving the key alone names a model the tier no longer holds, and
+    // serializeTierModelConfigs then drops the params on submit without saying so.
+    it("rewrites a param key to the same registered spelling its tier entry was rewritten to", () => {
+      const config = {
+        tiers: { SIMPLE: [], MEDIUM: [], COMPLEX: [], REASONING: ["claude-sonnet-4-5"] },
+        tier_model_configs: {
+          REASONING: [{ model_name: "claude-sonnet-4-5", litellm_params: { reasoning_effort: "high" } }],
+        },
+        classifier_type: "heuristic" as const,
+        session_affinity: false,
+        deployment_affinity: true,
+      };
+      const prefill = buildPresetPrefill(config, groupsOnly(["claude-sonnet-4.5"]));
+      expect(prefill.complexityRouterConfig.tier_model_params).toEqual({
+        REASONING: { "claude-sonnet-4.5": { reasoning_effort: "high" } },
+      });
+    });
+
+    // Two spellings of one model in a tier collapse to a single registered key, and one model can
+    // only hold one param set downstream. Merging keeps whatever only one spelling set instead of
+    // dropping that spelling's params wholesale.
+    it("merges rather than drops params when two spellings resolve to the same registered model", () => {
+      const config = {
+        tiers: { SIMPLE: [], MEDIUM: [], COMPLEX: [], REASONING: ["claude-sonnet-4-5", "claude-sonnet-4.5"] },
+        tier_model_configs: {
+          REASONING: [
+            { model_name: "claude-sonnet-4-5", litellm_params: { reasoning_effort: "high", temperature: 0.2 } },
+            { model_name: "claude-sonnet-4.5", litellm_params: { reasoning_effort: "low" } },
+          ],
+        },
+        classifier_type: "heuristic" as const,
+      };
+      const prefill = buildPresetPrefill(config, groupsOnly(["claude-sonnet-4.5"]));
+      // temperature survives from the spelling that would otherwise have been overwritten;
+      // reasoning_effort, set by both, resolves last-wins.
+      expect(prefill.complexityRouterConfig.tier_model_params).toEqual({
+        REASONING: { "claude-sonnet-4.5": { reasoning_effort: "low", temperature: 0.2 } },
+      });
+    });
+
+    it("leaves tier_model_params undefined for a preset that carries no per-model params", () => {
+      const config = {
+        tiers: { SIMPLE: ["gpt-5-nano"], MEDIUM: [], COMPLEX: [], REASONING: [] },
+        classifier_type: "heuristic" as const,
+        session_affinity: false,
+        deployment_affinity: true,
+      };
+      const prefill = buildPresetPrefill(config, groupsOnly(["gpt-5-nano"]));
+      expect(prefill.complexityRouterConfig.tier_model_params).toBeUndefined();
+    });
   });
 });
diff --git a/ui/litellm-dashboard/src/lib/autorouter_presets.ts b/ui/litellm-dashboard/src/lib/autorouter_presets.ts
index fd1ca7a13c2..a35b868db5e 100644
--- a/ui/litellm-dashboard/src/lib/autorouter_presets.ts
+++ b/ui/litellm-dashboard/src/lib/autorouter_presets.ts
@@ -12,6 +12,11 @@ import {
 } from "@/components/add_model/ComplexityRouterConfig";
 import { KeywordTierRule } from "@/components/add_model/KeywordTierRules";
 import { hydrateKeywordTierRules } from "@/components/add_model/complexity_router_keywords";
+import {
+  TierModelParams,
+  TierModelParamsByTier,
+  hydrateTierModelParams,
+} from "@/components/add_model/complexity_router_tiers";
 import { DEFAULT_ESCALATION_KEYWORDS } from "@/components/add_model/EscalationKeywords";
 import { DEFAULT_MATCH_THRESHOLD } from "@/components/add_model/SemanticKeywordMatching";
 import presetsRaw from "@/autorouter_presets.json";
@@ -54,7 +59,7 @@ export const getRequiredModels = (
 // differing only in that separator. Canonicalizing on "-" (the presets' own convention) lets both
 // spellings match without doing anything looser - two DIFFERENT model names never collide here,
 // only the punctuation within one version number does.
-const normalizeModelName = (model: string): string => model.replace(/(\d)\.(\d)/g, "$1-$2");
+export const normalizeModelName = (model: string): string => model.replace(/(\d)\.(\d)/g, "$1-$2");
 
 export interface DeploymentModelRef {
   modelGroup: string;
@@ -244,6 +249,25 @@ export const buildPresetPrefill = (
 ): PresetPrefill => {
   const resolve = (model: string): string => resolveAvailableModel(model, availability) ?? model;
   const resolveTier = (models: string[]): string[] => models.map(resolve);
+  // Params key on the model name the preset spells while every tier entry is rewritten to the
+  // caller's registered spelling, so the keys have to be rewritten the same way. Otherwise
+  // serializeTierModelConfigs drops them for naming a model the tier no longer holds.
+  //
+  // Two spellings in one tier can resolve to the same registered model, and one model holds one
+  // param set here and in the payload, so a collision has to collapse. Merge rather than replace:
+  // params only one spelling set still survive, and a key both set resolves last-wins, matching
+  // how hydrateTierModelParams already collapses two entries spelled identically.
+  const resolveParamKeys = (params: TierModelParamsByTier | undefined): TierModelParamsByTier | undefined =>
+    params &&
+    Object.fromEntries(
+      Object.entries(params).map(([tier, byModel]) => [
+        tier,
+        Object.entries(byModel).reduce<Record<string, TierModelParams>>((byResolved, [model, litellmParams]) => {
+          const resolved = resolve(model);
+          return { ...byResolved, [resolved]: { ...byResolved[resolved], ...litellmParams } };
+        }, {}),
+      ]),
+    );
 
   return {
     complexityRouterConfig: {
@@ -253,6 +277,7 @@ export const buildPresetPrefill = (
         COMPLEX: resolveTier(config.tiers.COMPLEX),
         REASONING: resolveTier(config.tiers.REASONING),
       },
+      tier_model_params: resolveParamKeys(hydrateTierModelParams(config.tiers, config.tier_model_configs)),
       tier_labels: hydrateTierLabels(config.tier_labels),
       classifier_type: config.classifier_type,
       classifier_llm_config: config.classifier_llm_config && {