diff --git a/docs/drivers/OpcUaClient.md b/docs/drivers/OpcUaClient.md
index d189f57c..85f6168d 100644
--- a/docs/drivers/OpcUaClient.md
+++ b/docs/drivers/OpcUaClient.md
@@ -53,6 +53,8 @@ for every field (security policy/mode, auth type, session timeout, keep-alive,
 browse root, node/depth caps). `ReconnectPeriod` was **deleted** (#676 — unused since #670 removed the SDK reconnect
 handler, and the AdminUI no longer shows it); stored configs that still carry `reconnectPeriod` keep parsing in the
 factory, the Test-Connect probe and the browse picker (unknown keys are skipped), and the form drops it on the next save.
+`ProbeTimeoutSeconds` (default 15, AdminUI "Probe timeout") caps the Test-Connect probe's deadline — it can shorten
+the budget the host hands the probe, never extend it (review 2026-10-21 O-4; it used to be authored and consumed by nothing).
 
 ### Endpoint address: the configured host and port win (#676)
 
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient/OpcUaClientDriverProbe.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient/OpcUaClientDriverProbe.cs
index 748ff0c3..e4695e7a 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient/OpcUaClientDriverProbe.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient/OpcUaClientDriverProbe.cs
@@ -51,7 +51,8 @@ public sealed class OpcUaClientDriverProbe : IDriverProbe
 
         // Bound the whole probe (both phases) by the caller timeout, independent of `ct` — a
         // stalled OPC UA endpoint that accepts TCP but never answers GetEndpoints must not block
-        // the probe when the caller passes CancellationToken.None.
+        // the probe when the caller passes CancellationToken.None. The config's ProbeTimeoutSeconds caps it (O-4).
+        timeout = EffectiveTimeout(timeout, opts.ProbeTimeoutSeconds);
         using var cts = CancellationTokenSource.CreateLinkedTokenSource(ct);
         cts.CancelAfter(timeout);
 
@@ -106,6 +107,23 @@ public sealed class OpcUaClientDriverProbe : IDriverProbe
         }
     }
 
+    /// <summary>
+    ///     R06:O-4 — the deadline the probe actually runs under: the caller's budget, tightened by the config's
+    ///     <see cref="OpcUaClientDriverOptions.ProbeTimeoutSeconds"/> when that is positive and shorter (it can only
+    ///     shorten the budget — the caller's own deadline fires regardless). A non-positive caller budget is floored
+    ///     to 1 s so the probe runs briefly rather than cancelling before it starts. Same rule as the Galaxy probe.
+    /// </summary>
+    /// <param name="callerTimeout">The budget the host handed the probe.</param>
+    /// <param name="configuredSeconds">The config's <c>ProbeTimeoutSeconds</c>; ignored when not positive.</param>
+    /// <returns>The effective probe deadline.</returns>
+    internal static TimeSpan EffectiveTimeout(TimeSpan callerTimeout, int configuredSeconds)
+    {
+        var caller = callerTimeout > TimeSpan.Zero ? callerTimeout : TimeSpan.FromSeconds(1);
+        if (configuredSeconds <= 0) return caller;
+        var configured = TimeSpan.FromSeconds(configuredSeconds);
+        return configured < caller ? configured : caller;
+    }
+
     /// <summary>
     ///     Builds a minimal <see cref="ApplicationConfiguration"/> suitable for unauthenticated
     ///     discovery (GetEndpoints). No PKI stores, no session certificate — discovery traffic
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientProbeTimeoutTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientProbeTimeoutTests.cs
new file mode 100644
index 00000000..584952b1
--- /dev/null
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientProbeTimeoutTests.cs
@@ -0,0 +1,54 @@
+using System.Diagnostics;
+using System.Net;
+using System.Net.Sockets;
+using Shouldly;
+using Xunit;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests;
+
+/// <summary>
+///     Review 2026-10-21 R06:O-4 — <c>ProbeTimeoutSeconds</c> was authored by the AdminUI and parsed, but consumed
+///     by nothing: the Test Connect probe ran on the caller's budget alone. It now caps the probe deadline (it can
+///     shorten the caller's budget, never extend it) — the same rule as the Galaxy probe.
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class OpcUaClientProbeTimeoutTests
+{
+    /// <summary>The effective deadline is the shorter of the caller's budget and the configured cap.</summary>
+    [Theory]
+    [InlineData(10, 30, 10)]   // caller shorter → caller wins
+    [InlineData(10, 2, 2)]     // config shorter → config caps
+    [InlineData(10, 0, 10)]    // unset config → caller
+    [InlineData(10, -1, 10)]   // nonsense config → caller
+    [InlineData(0, 5, 1)]      // no caller budget → 1 s floor beats a longer config
+    public void EffectiveTimeout_is_the_shorter_of_caller_and_config(int callerSeconds, int configSeconds, int expectedSeconds)
+        => OpcUaClientDriverProbe.EffectiveTimeout(TimeSpan.FromSeconds(callerSeconds), configSeconds)
+            .ShouldBe(TimeSpan.FromSeconds(expectedSeconds));
+
+    /// <summary>
+    ///     Against a port that accepts TCP but never speaks OPC UA, a 1 s configured cap returns long before the
+    ///     caller's 30 s budget — the discovery handshake does the waiting, so this exercises the real deadline path.
+    /// </summary>
+    [Fact]
+    public async Task Configured_cap_shortens_the_probe_against_a_silent_listener()
+    {
+        var listener = new TcpListener(IPAddress.Loopback, 0);
+        listener.Start();
+        try
+        {
+            var port = ((IPEndPoint)listener.LocalEndpoint).Port;
+            var config = $$"""{ "endpointUrl": "opc.tcp://127.0.0.1:{{port}}", "probeTimeoutSeconds": 1 }""";
+
+            var sw = Stopwatch.StartNew();
+            var result = await new OpcUaClientDriverProbe().ProbeAsync(config, TimeSpan.FromSeconds(30), TestContext.Current.CancellationToken);
+            sw.Stop();
+
+            result.Ok.ShouldBeFalse();
+            sw.Elapsed.ShouldBeLessThan(TimeSpan.FromSeconds(15), $"the 1 s configured cap must bound the probe (message: {result.Message})");
+        }
+        finally
+        {
+            listener.Stop();
+        }
+    }
+}