diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7e0f2912c88..4b1fc1900bd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -59,6 +59,7 @@ Docs: https://docs.openclaw.ai
 
 ### Fixes
 
+- Gateway/watch: suppress sync-I/O trace output during `pnpm gateway:watch --benchmark` unless explicitly requested, so CPU profiling no longer floods the terminal with stack traces.
 - Agents/OpenAI: default direct OpenAI Responses models to the SSE transport instead of WebSocket auto-selection, preventing pi runtime chat turns from hanging on servers where the WebSocket path stalls while the OpenAI HTTP stream works. Thanks @vincentkoc.
 - Channels/plugins: key bundled package-state probes, env/config presence, and read-only command defaults by channel id instead of manifest plugin id, preserving setup and native-command detection for channel plugins whose package id differs from the channel alias. Thanks @vincentkoc.
 - Docker: prune package-excluded plugin dist directories from runtime images unless the build explicitly opts that plugin in, so official external plugins such as Feishu stay install-on-demand instead of shipping partial metadata without compiled runtime output. Fixes #77424. Thanks @vincentkoc.
diff --git a/docs/help/debugging.md b/docs/help/debugging.md
index 073cfed9ce2..1e24d01dfc3 100644
--- a/docs/help/debugging.md
+++ b/docs/help/debugging.md
@@ -157,6 +157,9 @@ Use `--benchmark-dir <path>` when you want profiles somewhere else.
 Use `--benchmark-no-force` when you want the benchmarked child to skip the
 default `--force` port cleanup and fail fast if the Gateway port is already in
 use.
+Benchmark mode suppresses sync-I/O trace spam by default. Set
+`OPENCLAW_TRACE_SYNC_IO=1` with `--benchmark` when you explicitly want both CPU
+profiles and Node sync-I/O stack traces.
 
 The tmux wrapper carries common non-secret runtime selectors such as
 `OPENCLAW_PROFILE`, `OPENCLAW_CONFIG_PATH`, `OPENCLAW_STATE_DIR`,
diff --git a/scripts/gateway-watch-tmux.mjs b/scripts/gateway-watch-tmux.mjs
index b7f4b95dbe3..0aab8cd034f 100644
--- a/scripts/gateway-watch-tmux.mjs
+++ b/scripts/gateway-watch-tmux.mjs
@@ -97,6 +97,7 @@ const resolveGatewayWatchBenchmarkArgs = ({ args = [], env = process.env } = {})
   if (benchmarkFlagSeen) {
     nextEnv[RUN_NODE_CPU_PROF_DIR_ENV] =
       benchmarkDir || nextEnv[RUN_NODE_CPU_PROF_DIR_ENV] || DEFAULT_BENCHMARK_PROFILE_DIR;
+    nextEnv.OPENCLAW_TRACE_SYNC_IO ??= "0";
   }
   return {
     args: benchmarkNoForceSeen
diff --git a/src/infra/gateway-watch-tmux.test.ts b/src/infra/gateway-watch-tmux.test.ts
index 1e271eae8c1..99045a54cc1 100644
--- a/src/infra/gateway-watch-tmux.test.ts
+++ b/src/infra/gateway-watch-tmux.test.ts
@@ -89,6 +89,7 @@ describe("gateway-watch tmux wrapper", () => {
     expect(code).toBe(0);
     const command = spawnSync.mock.calls[1]?.[1]?.[6] as string;
     expect(command).toContain("'OPENCLAW_RUN_NODE_CPU_PROF_DIR=.artifacts/gateway-watch-profiles'");
+    expect(command).toContain("'OPENCLAW_TRACE_SYNC_IO=0'");
     expect(command).not.toContain("--benchmark");
     expect(command).toContain("'gateway'");
     expect(command).toContain("'--force'");
@@ -97,6 +98,31 @@ describe("gateway-watch tmux wrapper", () => {
     );
   });
 
+  it("preserves explicit sync I/O tracing in benchmark mode", () => {
+    const stdout = createOutput();
+    const stderr = createOutput();
+    const spawnSync = vi
+      .fn()
+      .mockReturnValueOnce({ status: 1, stdout: "", stderr: "" })
+      .mockReturnValueOnce({ status: 0, stdout: "", stderr: "" })
+      .mockReturnValueOnce({ status: 0, stdout: "", stderr: "" })
+      .mockReturnValueOnce({ status: 0, stdout: "", stderr: "" });
+
+    const code = runGatewayWatchTmuxMain({
+      args: ["gateway", "--force", "--benchmark"],
+      cwd: "/repo",
+      env: { OPENCLAW_TRACE_SYNC_IO: "1", SHELL: "/bin/zsh" },
+      nodePath: "/node",
+      spawnSync,
+      stderr: stderr.stream,
+      stdout: stdout.stream,
+    });
+
+    expect(code).toBe(0);
+    const command = spawnSync.mock.calls[1]?.[1]?.[6] as string;
+    expect(command).toContain("'OPENCLAW_TRACE_SYNC_IO=1'");
+  });
+
   it("can remove --force from benchmarked watch runs", () => {
     const stdout = createOutput();
     const stderr = createOutput();