diff --git a/src/config/defaults.ts b/src/config/defaults.ts
index d68be922f..a576a0221 100644
--- a/src/config/defaults.ts
+++ b/src/config/defaults.ts
@@ -211,18 +211,16 @@ export function applyModelDefaults(cfg: OpenClawConfig): OpenClawConfig {
   }
 
   const existingAgent = nextCfg.agents?.defaults;
-  if (!existingAgent) return mutated ? nextCfg : cfg;
-  const existingModels = existingAgent.models ?? {};
-  if (Object.keys(existingModels).length === 0) return mutated ? nextCfg : cfg;
+  const existingModels = existingAgent?.models ?? {};
 
   const nextModels: Record<string, { alias?: string }> = {
     ...existingModels,
   };
 
+  // Always apply default model aliases, creating entries if they don't exist
   for (const [alias, target] of Object.entries(DEFAULT_MODEL_ALIASES)) {
     const entry = nextModels[target];
-    if (!entry) continue;
-    if (entry.alias !== undefined) continue;
+    if (entry?.alias !== undefined) continue; // User already defined an alias
     nextModels[target] = { ...entry, alias };
     mutated = true;
   }
diff --git a/src/config/model-alias-defaults.test.ts b/src/config/model-alias-defaults.test.ts
index 82bff85da..890db53a1 100644
--- a/src/config/model-alias-defaults.test.ts
+++ b/src/config/model-alias-defaults.test.ts
@@ -4,6 +4,34 @@ import { applyModelDefaults } from "./defaults.js";
 import type { OpenClawConfig } from "./types.js";
 
 describe("applyModelDefaults", () => {
+  it("adds default aliases even when no user models are configured", () => {
+    // Regression test: previously applyModelDefaults returned early when
+    // agents.defaults.models was empty, causing cron jobs using aliases
+    // like "sonnet" to fail with "Unknown model" errors.
+    const cfg = {} satisfies MoltbotConfig;
+    const next = applyModelDefaults(cfg);
+
+    expect(next.agents?.defaults?.models?.["anthropic/claude-opus-4-5"]?.alias).toBe("opus");
+    expect(next.agents?.defaults?.models?.["anthropic/claude-sonnet-4-5"]?.alias).toBe("sonnet");
+    expect(next.agents?.defaults?.models?.["openai/gpt-5.2"]?.alias).toBe("gpt");
+    expect(next.agents?.defaults?.models?.["openai/gpt-5-mini"]?.alias).toBe("gpt-mini");
+    expect(next.agents?.defaults?.models?.["google/gemini-3-pro-preview"]?.alias).toBe("gemini");
+    expect(next.agents?.defaults?.models?.["google/gemini-3-flash-preview"]?.alias).toBe(
+      "gemini-flash",
+    );
+  });
+
+  it("adds default aliases when agents.defaults exists but models is empty", () => {
+    const cfg = {
+      agents: {
+        defaults: {},
+      },
+    } satisfies MoltbotConfig;
+    const next = applyModelDefaults(cfg);
+
+    expect(next.agents?.defaults?.models?.["anthropic/claude-sonnet-4-5"]?.alias).toBe("sonnet");
+  });
+
   it("adds default aliases when models are present", () => {
     const cfg = {
       agents: {