diff --git a/src/commands/google-gemini-model-default.ts b/src/commands/google-gemini-model-default.ts
index a343a29fb3b..385f1cc849d 100644
--- a/src/commands/google-gemini-model-default.ts
+++ b/src/commands/google-gemini-model-default.ts
@@ -1,44 +1,11 @@
 import type { OpenClawConfig } from "../config/config.js";
-import type { AgentModelListConfig } from "../config/types.js";
+import { applyAgentDefaultPrimaryModel } from "./model-default.js";
 
 export const GOOGLE_GEMINI_DEFAULT_MODEL = "google/gemini-3-pro-preview";
 
-function resolvePrimaryModel(model?: AgentModelListConfig | string): string | undefined {
-  if (typeof model === "string") {
-    return model;
-  }
-  if (model && typeof model === "object" && typeof model.primary === "string") {
-    return model.primary;
-  }
-  return undefined;
-}
-
 export function applyGoogleGeminiModelDefault(cfg: OpenClawConfig): {
   next: OpenClawConfig;
   changed: boolean;
 } {
-  const current = resolvePrimaryModel(cfg.agents?.defaults?.model)?.trim();
-  if (current === GOOGLE_GEMINI_DEFAULT_MODEL) {
-    return { next: cfg, changed: false };
-  }
-
-  return {
-    next: {
-      ...cfg,
-      agents: {
-        ...cfg.agents,
-        defaults: {
-          ...cfg.agents?.defaults,
-          model:
-            cfg.agents?.defaults?.model && typeof cfg.agents.defaults.model === "object"
-              ? {
-                  ...cfg.agents.defaults.model,
-                  primary: GOOGLE_GEMINI_DEFAULT_MODEL,
-                }
-              : { primary: GOOGLE_GEMINI_DEFAULT_MODEL },
-        },
-      },
-    },
-    changed: true,
-  };
+  return applyAgentDefaultPrimaryModel({ cfg, model: GOOGLE_GEMINI_DEFAULT_MODEL });
 }
diff --git a/src/commands/model-default.test.ts b/src/commands/model-default.test.ts
new file mode 100644
index 00000000000..dab27ae31e6
--- /dev/null
+++ b/src/commands/model-default.test.ts
@@ -0,0 +1,23 @@
+import { describe, expect, it } from "vitest";
+import type { OpenClawConfig } from "../config/config.js";
+import { applyAgentDefaultPrimaryModel } from "./model-default.js";
+
+describe("applyAgentDefaultPrimaryModel", () => {
+  it("does not mutate when already set", () => {
+    const cfg = { agents: { defaults: { model: { primary: "a/b" } } } } as OpenClawConfig;
+    const result = applyAgentDefaultPrimaryModel({ cfg, model: "a/b" });
+    expect(result.changed).toBe(false);
+    expect(result.next).toBe(cfg);
+  });
+
+  it("normalizes legacy models", () => {
+    const cfg = { agents: { defaults: { model: { primary: "legacy" } } } } as OpenClawConfig;
+    const result = applyAgentDefaultPrimaryModel({
+      cfg,
+      model: "a/b",
+      legacyModels: new Set(["legacy"]),
+    });
+    expect(result.changed).toBe(false);
+    expect(result.next).toBe(cfg);
+  });
+});
diff --git a/src/commands/model-default.ts b/src/commands/model-default.ts
new file mode 100644
index 00000000000..ce121973da3
--- /dev/null
+++ b/src/commands/model-default.ts
@@ -0,0 +1,45 @@
+import type { OpenClawConfig } from "../config/config.js";
+import type { AgentModelListConfig } from "../config/types.js";
+
+export function resolvePrimaryModel(model?: AgentModelListConfig | string): string | undefined {
+  if (typeof model === "string") {
+    return model;
+  }
+  if (model && typeof model === "object" && typeof model.primary === "string") {
+    return model.primary;
+  }
+  return undefined;
+}
+
+export function applyAgentDefaultPrimaryModel(params: {
+  cfg: OpenClawConfig;
+  model: string;
+  legacyModels?: Set<string>;
+}): { next: OpenClawConfig; changed: boolean } {
+  const current = resolvePrimaryModel(params.cfg.agents?.defaults?.model)?.trim();
+  const normalizedCurrent = current && params.legacyModels?.has(current) ? params.model : current;
+  if (normalizedCurrent === params.model) {
+    return { next: params.cfg, changed: false };
+  }
+
+  return {
+    next: {
+      ...params.cfg,
+      agents: {
+        ...params.cfg.agents,
+        defaults: {
+          ...params.cfg.agents?.defaults,
+          model:
+            params.cfg.agents?.defaults?.model &&
+            typeof params.cfg.agents.defaults.model === "object"
+              ? {
+                  ...params.cfg.agents.defaults.model,
+                  primary: params.model,
+                }
+              : { primary: params.model },
+        },
+      },
+    },
+    changed: true,
+  };
+}
diff --git a/src/commands/opencode-zen-model-default.ts b/src/commands/opencode-zen-model-default.ts
index 9f3d4b45654..9efb9c17ade 100644
--- a/src/commands/opencode-zen-model-default.ts
+++ b/src/commands/opencode-zen-model-default.ts
@@ -1,5 +1,5 @@
 import type { OpenClawConfig } from "../config/config.js";
-import type { AgentModelListConfig } from "../config/types.js";
+import { applyAgentDefaultPrimaryModel } from "./model-default.js";
 
 export const OPENCODE_ZEN_DEFAULT_MODEL = "opencode/claude-opus-4-6";
 const LEGACY_OPENCODE_ZEN_DEFAULT_MODELS = new Set([
@@ -7,46 +7,13 @@ const LEGACY_OPENCODE_ZEN_DEFAULT_MODELS = new Set([
   "opencode-zen/claude-opus-4-5",
 ]);
 
-function resolvePrimaryModel(model?: AgentModelListConfig | string): string | undefined {
-  if (typeof model === "string") {
-    return model;
-  }
-  if (model && typeof model === "object" && typeof model.primary === "string") {
-    return model.primary;
-  }
-  return undefined;
-}
-
 export function applyOpencodeZenModelDefault(cfg: OpenClawConfig): {
   next: OpenClawConfig;
   changed: boolean;
 } {
-  const current = resolvePrimaryModel(cfg.agents?.defaults?.model)?.trim();
-  const normalizedCurrent =
-    current && LEGACY_OPENCODE_ZEN_DEFAULT_MODELS.has(current)
-      ? OPENCODE_ZEN_DEFAULT_MODEL
-      : current;
-  if (normalizedCurrent === OPENCODE_ZEN_DEFAULT_MODEL) {
-    return { next: cfg, changed: false };
-  }
-
-  return {
-    next: {
-      ...cfg,
-      agents: {
-        ...cfg.agents,
-        defaults: {
-          ...cfg.agents?.defaults,
-          model:
-            cfg.agents?.defaults?.model && typeof cfg.agents.defaults.model === "object"
-              ? {
-                  ...cfg.agents.defaults.model,
-                  primary: OPENCODE_ZEN_DEFAULT_MODEL,
-                }
-              : { primary: OPENCODE_ZEN_DEFAULT_MODEL },
-        },
-      },
-    },
-    changed: true,
-  };
+  return applyAgentDefaultPrimaryModel({
+    cfg,
+    model: OPENCODE_ZEN_DEFAULT_MODEL,
+    legacyModels: LEGACY_OPENCODE_ZEN_DEFAULT_MODELS,
+  });
 }