diff --git a/src/hooks/think-mode/index.test.ts b/src/hooks/think-mode/index.test.ts
index e135412db4..911c4dce61 100644
--- a/src/hooks/think-mode/index.test.ts
+++ b/src/hooks/think-mode/index.test.ts
@@ -153,3 +153,50 @@ describe("createThinkModeHook", () => {
     expect(output.message.model).toBeUndefined()
   })
 })
+
+describe("think-mode: regression tests for issue #2382", () => {
+  const sessionID = "regression-2382"
+
+  beforeEach(() => {
+    clearThinkModeState(sessionID)
+  })
+
+  it("does NOT upgrade gpt-5-nano on Korean think-mode trigger text", async () => {
+    const hook = createThinkModeHook()
+    const input = createHookInput({
+      sessionID,
+      providerID: "opencode",
+      modelID: "gpt-5-nano",
+    })
+    const output = createHookOutput(
+      "너와 인공지능 엔진에게 이미지와 참조 자료를 어떻게 전달할지 고민하고 있었는데"
+    )
+
+    // when
+    await hook["chat.message"](input, output)
+
+    expect(output.message.variant).toBeUndefined()
+    expect(output.message.model).toBeUndefined()
+  })
+
+  it("still upgrades claude-sonnet-4-6 on the same Korean think-mode trigger text", async () => {
+    const hook = createThinkModeHook()
+    const input = createHookInput({
+      sessionID,
+      providerID: "anthropic",
+      modelID: "claude-sonnet-4-6",
+    })
+    const output = createHookOutput(
+      "너와 인공지능 엔진에게 이미지와 참조 자료를 어떻게 전달할지 고민하고 있었는데"
+    )
+
+    // when
+    await hook["chat.message"](input, output)
+
+    expect(output.message.variant).toBe("high")
+    expect(output.message.model).toEqual({
+      providerID: "anthropic",
+      modelID: "claude-sonnet-4-6-high",
+    })
+  })
+})
diff --git a/src/hooks/think-mode/switcher.test.ts b/src/hooks/think-mode/switcher.test.ts
index e56ec5823d..670717e0f3 100644
--- a/src/hooks/think-mode/switcher.test.ts
+++ b/src/hooks/think-mode/switcher.test.ts
@@ -69,6 +69,13 @@ describe("think-mode switcher", () => {
         expect(getHighVariant("llama-3-70b")).toBeNull()
         expect(getHighVariant("mistral-large")).toBeNull()
       })
+
+      it("should return null for gpt-5-nano (no reasoning variant on Zen)", () => {
+        // given gpt-5-nano — a lightweight model with no high variant on OpenCode Zen
+        // see: https://github.com/code-yeongyu/oh-my-openagent/issues/2382
+        expect(getHighVariant("gpt-5-nano")).toBeNull()
+        expect(getHighVariant("opencode/gpt-5-nano")).toBeNull()
+      })
     })
   })
 
diff --git a/src/hooks/think-mode/switcher.ts b/src/hooks/think-mode/switcher.ts
index f458d9b663..fe4ff28645 100644
--- a/src/hooks/think-mode/switcher.ts
+++ b/src/hooks/think-mode/switcher.ts
@@ -50,9 +50,11 @@ const HIGH_VARIANT_MAP: Record<string, string> = {
    "gemini-3-1-pro-low": "gemini-3-1-pro-high",
    "gemini-3-flash": "gemini-3-flash-high",
   // GPT-5
+  // NOTE: gpt-5-nano is intentionally excluded — it is a lightweight nano model
+  // that does not have a reasoning/high-effort variant on the OpenCode Zen provider.
+  // Mapping it to gpt-5-nano-high causes a "Model not found" error.
   "gpt-5": "gpt-5-high",
   "gpt-5-mini": "gpt-5-mini-high",
-  "gpt-5-nano": "gpt-5-nano-high",
   "gpt-5-pro": "gpt-5-pro-high",
   "gpt-5-chat-latest": "gpt-5-chat-latest-high",
   // GPT-5.1