diff --git a/docs/integration/heicode-am-contract.md b/docs/integration/heicode-am-contract.md
index ce992d82..d092bae7 100644
--- a/docs/integration/heicode-am-contract.md
+++ b/docs/integration/heicode-am-contract.md
@@ -79,7 +79,7 @@ HM 把用户绑定的资源按**资源类型 + provider**解成固定 env 名(
 | database | postgres | `POSTGRES_HOST` `POSTGRES_PORT` `POSTGRES_DATABASE` `POSTGRES_USER` · `POSTGRES_PASSWORD`(密) |
 | storage | azure blob | `AZURE_BLOB_ACCOUNT_NAME` `AZURE_BLOB_CONTAINER` · `AZURE_BLOB_ACCOUNT_KEY`(密) |
 
-另外随启动注入(模型网关):`OPENAI_BASE_URL`(= HM `/v1`)、`MODEL_NAME`。**`OPENAI_API_KEY` 不在启动时注入** —— 由客户端在 A2A 请求里带 `api_key`(你们文档 §7);后续若走 V2 解密路径再调整。
+另外随启动注入(模型网关):`OPENAI_BASE_URL`(= HM `/v1`)、`MODEL_NAME`(**默认 `gpt-5.4`**,可用 env `AGENT_RUNTIME_DEFAULT_MODEL` 覆盖;模板 frontmatter 里的 `opus/sonnet` 只是角色提示,**不会**当作网关模型传)。**`OPENAI_API_KEY` 不在启动时注入** —— 由客户端在 A2A 请求里带 `api_key`(你们文档 §7);后续若走 V2 解密路径再调整。
 
 - 缺失的可选字段不会出现在 env 里(agent 自行容错)。
 - 同类型资源 HM 限制只挂一个(避免 env 名冲突)。
diff --git a/heicode/controller/agent_template_runtime.go b/heicode/controller/agent_template_runtime.go
index 13dc1669..4ace5ec0 100644
--- a/heicode/controller/agent_template_runtime.go
+++ b/heicode/controller/agent_template_runtime.go
@@ -148,9 +148,17 @@ func amStartTemplateAgent(ctx context.Context, args amStartArgs) (amStartResult,
 	if strings.TrimSpace(args.AgentDefinition) != "" {
 		env["AGENT_INSTRUCTION_TEXT"] = args.AgentDefinition
 	}
-	if args.Model != "" {
-		env["MODEL_NAME"] = args.Model
+	// MODEL_NAME must be a real model on the HM gateway. Template frontmatter
+	// carries a Claude-style tier hint (opus/sonnet/haiku) which is NOT a gateway
+	// model — fall back to the gateway default (gpt-5.4, env-overridable).
+	modelName := common.GetEnvOrDefaultString("AGENT_RUNTIME_DEFAULT_MODEL", "gpt-5.4")
+	switch strings.ToLower(strings.TrimSpace(args.Model)) {
+	case "", "opus", "sonnet", "haiku", "claude":
+		// keep the gateway default
+	default:
+		modelName = strings.TrimSpace(args.Model)
 	}
+	env["MODEL_NAME"] = modelName
 	env["OPENAI_BASE_URL"] = publicV1BaseURL()
 	// NOTE: OPENAI_API_KEY is intentionally NOT injected here — the desktop
 	// client passes its own api_key per A2A request (CODING_A2A §7). A future
diff --git a/heicode/controller/agent_template_test.go b/heicode/controller/agent_template_test.go
index f56c0f16..837717e9 100644
--- a/heicode/controller/agent_template_test.go
+++ b/heicode/controller/agent_template_test.go
@@ -169,12 +169,33 @@ func TestAMStartTemplateAgent_RoundTrip(t *testing.T) {
 	require.Contains(t, gotBody, "AGENT_ROLE_NAME")
 	require.Contains(t, gotBody, "OPENAI_BASE_URL")
 	require.Contains(t, gotBody, "manager_deployment_id")
+	require.Contains(t, gotBody, `"MODEL_NAME":"gpt-5.4"`) // real gateway model
 	// response parsed
 	require.Equal(t, "ns-1", res.RuntimeID)
 	require.Equal(t, "https://abc.agents.example", res.Subdomain)
 	require.Equal(t, "running", res.Status) // defaulted
 }
 
+func TestAMStartTemplateAgent_ModelDefaultsToGateway(t *testing.T) {
+	var gotBody string
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		b, _ := io.ReadAll(r.Body)
+		gotBody = string(b)
+		_, _ = w.Write([]byte(`{"success":true,"data":{"namespace":"ns"}}`))
+	}))
+	defer srv.Close()
+	t.Setenv("AGENT_RUNTIME_BASE_URL", srv.URL)
+
+	// template frontmatter model "opus" is a Claude tier, not a gateway model.
+	_, err := amStartTemplateAgent(context.Background(), amStartArgs{
+		ManagerDeploymentID: "dep_1", UserID: "22", TemplateKey: "architect",
+		AgentDefinition: "x", Model: "opus",
+	})
+	require.NoError(t, err)
+	require.Contains(t, gotBody, `"MODEL_NAME":"gpt-5.4"`) // defaulted, not "opus"
+	require.NotContains(t, gotBody, `"MODEL_NAME":"opus"`)
+}
+
 func TestAMGetAgentStatus_RoundTrip(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		require.Equal(t, "/agents/rt-1", r.URL.Path)