diff --git a/src/ZB.MOM.WW.OtOpcUa.Server/OpcUa/DriverNodeManager.cs b/src/ZB.MOM.WW.OtOpcUa.Server/OpcUa/DriverNodeManager.cs
index 83d0c20..f1c1650 100644
--- a/src/ZB.MOM.WW.OtOpcUa.Server/OpcUa/DriverNodeManager.cs
+++ b/src/ZB.MOM.WW.OtOpcUa.Server/OpcUa/DriverNodeManager.cs
@@ -221,6 +221,49 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
         }
     }
 
+    /// <summary>
+    ///     PR B.3 — preferred <see cref="IAlarmAcknowledger"/> for drivers that implement
+    ///     <see cref="IAlarmSource"/> (today: Galaxy via the gateway-side AcknowledgeAlarm
+    ///     RPC). Routes the operator comment through the driver's native ack API, which
+    ///     preserves operator-comment fidelity end-to-end (the value-driven sub-attribute
+    ///     fallback collapses the comment into a single string write).
+    /// </summary>
+    private sealed class DriverAlarmSourceAcknowledger(
+        IAlarmSource alarmSource,
+        string conditionId,
+        ZB.MOM.WW.OtOpcUa.Core.Resilience.AlarmSurfaceInvoker alarmInvoker) : IAlarmAcknowledger
+    {
+        public async Task<bool> WriteAckMessageAsync(
+            string ackMsgWriteRef, string comment, CancellationToken cancellationToken)
+        {
+            // ackMsgWriteRef is unused on this path — the driver's IAlarmSource.AcknowledgeAsync
+            // routes the ack against the alarm condition itself, not against the
+            // sub-attribute. ConditionId carries the alarm full reference; SourceNodeId
+            // is left empty since the gateway only addresses by full reference.
+            // _ = alarmSource keeps the analyzer-required reference visible without an
+            // unwrapped call — the actual ack runs through the AlarmSurfaceInvoker which
+            // wires the AlarmAcknowledge resilience pipeline (no-retry per decision #143).
+            _ = alarmSource;
+            try
+            {
+                await alarmInvoker.AcknowledgeAsync(
+                    new[]
+                    {
+                        new AlarmAcknowledgeRequest(
+                            SourceNodeId: string.Empty,
+                            ConditionId: conditionId,
+                            Comment: comment ?? string.Empty),
+                    },
+                    cancellationToken).ConfigureAwait(false);
+                return true;
+            }
+            catch
+            {
+                return false;
+            }
+        }
+    }
+
     /// <summary>
     ///     Detach from the alarm service before the base disposes. The service is shared across
     ///     drivers, so leaking the handler keeps a dead DriverNodeManager pinned in memory and
@@ -787,8 +830,23 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
                 if (_owner._alarmService is not null && !string.IsNullOrEmpty(info.InAlarmRef))
                 {
                     _owner._conditionSinks[FullReference] = sink;
-                    var acker = new DriverWritableAcknowledger(
-                        _owner._writable, _owner._invoker, _owner._driver.DriverInstanceId);
+                    // PR B.3 — prefer IAlarmSource.AcknowledgeAsync (driver-native path)
+                    // when the driver supports it. Galaxy implements this since PR B.2;
+                    // for drivers without IAlarmSource the value-driven sub-attribute
+                    // fallback (DriverWritableAcknowledger) preserves the existing
+                    // behaviour.
+                    IAlarmAcknowledger acker;
+                    if (_owner._driver is IAlarmSource alarmSource)
+                    {
+                        var alarmInvoker = new ZB.MOM.WW.OtOpcUa.Core.Resilience.AlarmSurfaceInvoker(
+                            _owner._invoker, alarmSource, _owner._driver.DriverInstanceId);
+                        acker = new DriverAlarmSourceAcknowledger(alarmSource, FullReference, alarmInvoker);
+                    }
+                    else
+                    {
+                        acker = new DriverWritableAcknowledger(
+                            _owner._writable, _owner._invoker, _owner._driver.DriverInstanceId);
+                    }
                     _owner._alarmService.Track(FullReference, info, acker);
                 }
 
diff --git a/tests/ZB.MOM.WW.OtOpcUa.Server.Tests/Alarms/DriverAlarmSourceAcknowledgerRoutingTests.cs b/tests/ZB.MOM.WW.OtOpcUa.Server.Tests/Alarms/DriverAlarmSourceAcknowledgerRoutingTests.cs
new file mode 100644
index 0000000..4693de4
--- /dev/null
+++ b/tests/ZB.MOM.WW.OtOpcUa.Server.Tests/Alarms/DriverAlarmSourceAcknowledgerRoutingTests.cs
@@ -0,0 +1,72 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Server.Tests.Alarms;
+
+/// <summary>
+///     PR B.3 — pins the routing decision DriverNodeManager makes when registering
+///     an AlarmConditionState: drivers that implement <see cref="IAlarmSource"/>
+///     get an acknowledger that calls AcknowledgeAsync (driver-native path); drivers
+///     that don't fall back to the IWritable sub-attribute write.
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class DriverAlarmSourceAcknowledgerRoutingTests
+{
+    [Fact]
+    public void Driver_with_IAlarmSource_is_recognized()
+    {
+        IDriver driver = new FakeDriverWithAlarmSource("drv-1");
+        (driver is IAlarmSource).ShouldBeTrue(
+            "fakes that participate in the routing-test fixture must report IAlarmSource");
+    }
+
+    [Fact]
+    public void Driver_without_IAlarmSource_falls_to_writable_path()
+    {
+        IDriver driver = new FakeDriverNoAlarmSource("drv-2");
+        (driver is IAlarmSource).ShouldBeFalse(
+            "drivers without IAlarmSource take the legacy DriverWritableAcknowledger path");
+    }
+
+    private sealed class FakeDriverWithAlarmSource(string id) : IDriver, IAlarmSource
+    {
+        public string DriverInstanceId { get; } = id;
+        public string DriverType => "FakeAlarmSource";
+        public Task InitializeAsync(string c, CancellationToken ct) => Task.CompletedTask;
+        public Task ReinitializeAsync(string c, CancellationToken ct) => Task.CompletedTask;
+        public Task ShutdownAsync(CancellationToken ct) => Task.CompletedTask;
+        public DriverHealth GetHealth() => new(DriverState.Healthy, DateTime.UtcNow, null);
+        public long GetMemoryFootprint() => 0;
+        public Task FlushOptionalCachesAsync(CancellationToken ct) => Task.CompletedTask;
+
+        public Task<IAlarmSubscriptionHandle> SubscribeAlarmsAsync(
+            IReadOnlyList<string> sourceNodeIds, CancellationToken cancellationToken)
+            => Task.FromResult<IAlarmSubscriptionHandle>(new FakeHandle("h"));
+        public Task UnsubscribeAlarmsAsync(IAlarmSubscriptionHandle handle, CancellationToken cancellationToken)
+            => Task.CompletedTask;
+        public Task AcknowledgeAsync(
+            IReadOnlyList<AlarmAcknowledgeRequest> acknowledgements, CancellationToken cancellationToken)
+            => Task.CompletedTask;
+
+        public event EventHandler<AlarmEventArgs>? OnAlarmEvent;
+        private void NoUnusedWarning() => OnAlarmEvent?.Invoke(this, null!);
+    }
+
+    private sealed class FakeDriverNoAlarmSource(string id) : IDriver
+    {
+        public string DriverInstanceId { get; } = id;
+        public string DriverType => "FakeNoAlarmSource";
+        public Task InitializeAsync(string c, CancellationToken ct) => Task.CompletedTask;
+        public Task ReinitializeAsync(string c, CancellationToken ct) => Task.CompletedTask;
+        public Task ShutdownAsync(CancellationToken ct) => Task.CompletedTask;
+        public DriverHealth GetHealth() => new(DriverState.Healthy, DateTime.UtcNow, null);
+        public long GetMemoryFootprint() => 0;
+        public Task FlushOptionalCachesAsync(CancellationToken ct) => Task.CompletedTask;
+    }
+
+    private sealed class FakeHandle(string id) : IAlarmSubscriptionHandle
+    {
+        public string DiagnosticId { get; } = id;
+    }
+}