diff --git a/src/cli/update-cli/update-command.ts b/src/cli/update-cli/update-command.ts
index 8106db65048..7df3b7ecacb 100644
--- a/src/cli/update-cli/update-command.ts
+++ b/src/cli/update-cli/update-command.ts
@@ -1422,7 +1422,9 @@ async function runPackageInstallUpdate(params: {
             OPENCLAW_UPDATE_IN_PROGRESS: "1",
             [UPDATE_DEFER_CONFIGURED_PLUGIN_INSTALL_REPAIR_ENV]: "1",
             [UPDATE_PARENT_SUPPORTS_DOCTOR_CONFIG_WRITE_ENV]: "1",
-            OPENCLAW_COMPATIBILITY_HOST_VERSION: candidateHostVersion,
+            ...(candidateHostVersion === null
+              ? {}
+              : { OPENCLAW_COMPATIBILITY_HOST_VERSION: candidateHostVersion }),
           },
           timeoutMs: params.timeoutMs,
           progress: params.progress,
diff --git a/src/infra/update-runner.ts b/src/infra/update-runner.ts
index da7817bda81..4c96082f1f9 100644
--- a/src/infra/update-runner.ts
+++ b/src/infra/update-runner.ts
@@ -1487,7 +1487,9 @@ export async function runGatewayUpdate(opts: UpdateRunnerOptions = {}): Promise<
           env: {
             OPENCLAW_UPDATE_IN_PROGRESS: "1",
             [UPDATE_PARENT_SUPPORTS_DOCTOR_CONFIG_WRITE_ENV]: "1",
-            OPENCLAW_COMPATIBILITY_HOST_VERSION: candidateHostVersion,
+            ...(candidateHostVersion === null
+              ? {}
+              : { OPENCLAW_COMPATIBILITY_HOST_VERSION: candidateHostVersion }),
           },
           progress,
           stepIndex: 0,