diff --git a/packages/contracts/src/model.test.ts b/packages/contracts/src/model.test.ts
index 2f31b6ebe35a5c12c7f6c9dbdec74a051fb39d63..137167daa577a9b3aff5e77d9201a805a483c203 100644
--- a/packages/contracts/src/model.test.ts
+++ b/packages/contracts/src/model.test.ts
@@ -1,6 +1,16 @@
 import { describe, expect, it } from "vitest";
 
-import { DEFAULT_MODEL, MODEL_OPTIONS, normalizeModelSlug, resolveModelSlug } from "./model";
+import {
+  DEFAULT_MODEL,
+  DEFAULT_MODEL_BY_PROVIDER,
+  MODEL_OPTIONS,
+  MODEL_OPTIONS_BY_PROVIDER,
+  getDefaultModel,
+  getModelOptions,
+  normalizeModelSlug,
+  resolveModelSlug,
+  resolveModelSlugForProvider,
+} from "./model";
 
 describe("normalizeModelSlug", () => {
   it("maps known aliases to canonical slugs", () => {
@@ -19,6 +29,11 @@ describe("normalizeModelSlug", () => {
     expect(normalizeModelSlug("gpt-5.2")).toBe("gpt-5.2");
     expect(normalizeModelSlug("gpt-5.2-codex")).toBe("gpt-5.2-codex");
   });
+
+  it("uses provider-specific aliases", () => {
+    expect(normalizeModelSlug("sonnet", "claudeCode")).toBe("claude-sonnet-4-5");
+    expect(normalizeModelSlug("opus-4.1", "claudeCode")).toBe("claude-opus-4-1");
+  });
 });
 
 describe("resolveModelSlug", () => {
@@ -37,4 +52,20 @@ describe("resolveModelSlug", () => {
       expect(resolveModelSlug(model.slug)).toBe(model.slug);
     }
   });
+
+  it("supports provider-aware resolution", () => {
+    expect(resolveModelSlugForProvider("claudeCode", undefined)).toBe(
+      DEFAULT_MODEL_BY_PROVIDER.claudeCode,
+    );
+    expect(resolveModelSlugForProvider("claudeCode", "sonnet")).toBe("claude-sonnet-4-5");
+    expect(resolveModelSlugForProvider("claudeCode", "gpt-5.3-codex")).toBe(
+      DEFAULT_MODEL_BY_PROVIDER.claudeCode,
+    );
+  });
+
+  it("keeps codex defaults for backward compatibility", () => {
+    expect(getDefaultModel()).toBe(DEFAULT_MODEL);
+    expect(getModelOptions()).toEqual(MODEL_OPTIONS);
+    expect(getModelOptions("claudeCode")).toEqual(MODEL_OPTIONS_BY_PROVIDER.claudeCode);
+  });
 });
diff --git a/packages/contracts/src/model.ts b/packages/contracts/src/model.ts
index cf019e98bd611795c3fab42d257507c64c1f9bfb..3626e4c5a78e256c5c9267148e3227fa9350b84b 100644
--- a/packages/contracts/src/model.ts
+++ b/packages/contracts/src/model.ts
@@ -1,23 +1,72 @@
-export const MODEL_OPTIONS = [
-  { slug: "gpt-5.3-codex", name: "GPT-5.3 Codex" },
-  { slug: "gpt-5.3-codex-spark", name: "GPT-5.3 Codex Spark" },
-  { slug: "gpt-5.2-codex", name: "GPT-5.2 Codex" },
-  { slug: "gpt-5.2", name: "GPT-5.2" },
-] as const;
-
-export type BuiltInModelSlug = (typeof MODEL_OPTIONS)[number]["slug"];
-export type ModelSlug = string;
-
-export const DEFAULT_MODEL = "gpt-5.3-codex";
-
-export const MODEL_SLUG_ALIASES: Record<string, BuiltInModelSlug> = {
-  "5.3": "gpt-5.3-codex",
-  "gpt-5.3": "gpt-5.3-codex",
-  "5.3-spark": "gpt-5.3-codex-spark",
-  "gpt-5.3-spark": "gpt-5.3-codex-spark",
+import type { ProviderKind } from "./orchestration";
+
+type ModelOption = {
+  readonly slug: string;
+  readonly name: string;
+};
+
+export const MODEL_OPTIONS_BY_PROVIDER = {
+  codex: [
+    { slug: "gpt-5.3-codex", name: "GPT-5.3 Codex" },
+    { slug: "gpt-5.3-codex-spark", name: "GPT-5.3 Codex Spark" },
+    { slug: "gpt-5.2-codex", name: "GPT-5.2 Codex" },
+    { slug: "gpt-5.2", name: "GPT-5.2" },
+  ],
+  claudeCode: [
+    { slug: "claude-sonnet-4-5", name: "Claude Sonnet 4.5" },
+    { slug: "claude-opus-4-1", name: "Claude Opus 4.1" },
+    { slug: "claude-haiku-3-5", name: "Claude Haiku 3.5" },
+  ],
+} as const satisfies Record<ProviderKind, readonly ModelOption[]>;
+
+export type ModelSlug = (typeof MODEL_OPTIONS_BY_PROVIDER)[ProviderKind][number]["slug"];
+
+export const DEFAULT_MODEL_BY_PROVIDER: Record<ProviderKind, ModelSlug> = {
+  codex: "gpt-5.3-codex",
+  claudeCode: "claude-sonnet-4-5",
+};
+
+// Backward compatibility for existing Codex-only call sites.
+export const MODEL_OPTIONS = MODEL_OPTIONS_BY_PROVIDER.codex;
+export const DEFAULT_MODEL = DEFAULT_MODEL_BY_PROVIDER.codex;
+
+export const MODEL_SLUG_ALIASES_BY_PROVIDER: Record<ProviderKind, Record<string, ModelSlug>> = {
+  codex: {
+    "5.3": "gpt-5.3-codex",
+    "gpt-5.3": "gpt-5.3-codex",
+    "5.3-spark": "gpt-5.3-codex-spark",
+    "gpt-5.3-spark": "gpt-5.3-codex-spark",
+  },
+  claudeCode: {
+    sonnet: "claude-sonnet-4-5",
+    "sonnet-4.5": "claude-sonnet-4-5",
+    "claude-sonnet-4.5": "claude-sonnet-4-5",
+    opus: "claude-opus-4-1",
+    "opus-4.1": "claude-opus-4-1",
+    "claude-opus-4.1": "claude-opus-4-1",
+    haiku: "claude-haiku-3-5",
+    "haiku-3.5": "claude-haiku-3-5",
+    "claude-haiku-3.5": "claude-haiku-3-5",
+  },
+};
+
+const MODEL_SLUG_SET_BY_PROVIDER: Record<ProviderKind, ReadonlySet<ModelSlug>> = {
+  codex: new Set(MODEL_OPTIONS_BY_PROVIDER.codex.map((option) => option.slug)),
+  claudeCode: new Set(MODEL_OPTIONS_BY_PROVIDER.claudeCode.map((option) => option.slug)),
 };
 
-export function normalizeModelSlug(model: string | null | undefined): ModelSlug | null {
+export function getModelOptions(provider: ProviderKind = "codex") {
+  return MODEL_OPTIONS_BY_PROVIDER[provider];
+}
+
+export function getDefaultModel(provider: ProviderKind = "codex"): ModelSlug {
+  return DEFAULT_MODEL_BY_PROVIDER[provider];
+}
+
+export function normalizeModelSlug(
+  model: string | null | undefined,
+  provider: ProviderKind = "codex",
+): ModelSlug | null {
   if (typeof model !== "string") {
     return null;
   }
@@ -27,12 +76,28 @@ export function normalizeModelSlug(model: string | null | undefined): ModelSlug
     return null;
   }
 
-  return MODEL_SLUG_ALIASES[trimmed] ?? trimmed;
+  return MODEL_SLUG_ALIASES_BY_PROVIDER[provider][trimmed] ?? (trimmed as ModelSlug);
 }
 
-export function resolveModelSlug(model: string | null | undefined): ModelSlug {
-  const normalized = normalizeModelSlug(model);
-  return normalized ?? DEFAULT_MODEL;
+export function resolveModelSlug(
+  model: string | null | undefined,
+  provider: ProviderKind = "codex",
+): ModelSlug {
+  const normalized = normalizeModelSlug(model, provider);
+  if (!normalized) {
+    return DEFAULT_MODEL_BY_PROVIDER[provider];
+  }
+
+  return MODEL_SLUG_SET_BY_PROVIDER[provider].has(normalized)
+    ? normalized
+    : DEFAULT_MODEL_BY_PROVIDER[provider];
+}
+
+export function resolveModelSlugForProvider(
+  provider: ProviderKind,
+  model: string | null | undefined,
+): ModelSlug {
+  return resolveModelSlug(model, provider);
 }
 
 export const REASONING_OPTIONS = ["xhigh", "high", "medium", "low"] as const;