diff --git a/clients/dotnet/MxGateway.Client.Tests/FakeGatewayTransport.cs b/clients/dotnet/MxGateway.Client.Tests/FakeGatewayTransport.cs
index 554d6a1..c21f2a4 100644
--- a/clients/dotnet/MxGateway.Client.Tests/FakeGatewayTransport.cs
+++ b/clients/dotnet/MxGateway.Client.Tests/FakeGatewayTransport.cs
@@ -47,9 +47,9 @@ internal sealed class FakeGatewayTransport(MxGatewayClientOptions options) : IMx
     public List<(AcknowledgeAlarmRequest Request, CallOptions CallOptions)> AcknowledgeAlarmCalls { get; } = [];
 
     /// <summary>
-    /// Gets the list of captured QueryActiveAlarmsAsync calls.
+    /// Gets the list of captured StreamAlarmsAsync calls.
     /// </summary>
-    public List<(QueryActiveAlarmsRequest Request, CallOptions CallOptions)> QueryActiveAlarmsCalls { get; } = [];
+    public List<(StreamAlarmsRequest Request, CallOptions CallOptions)> StreamAlarmsCalls { get; } = [];
 
     /// <summary>
     /// Gets the queue of exceptions to throw from AcknowledgeAlarmAsync.
@@ -223,7 +223,6 @@ internal sealed class FakeGatewayTransport(MxGatewayClientOptions options) : IMx
             ? _acknowledgeReplies.Dequeue()
             : new AcknowledgeAlarmReply
             {
-                SessionId = request.SessionId,
                 CorrelationId = request.ClientCorrelationId,
                 ProtocolStatus = new ProtocolStatus { Code = ProtocolStatusCode.Ok },
                 Status = new MxStatusProxy { Success = 1, Category = MxStatusCategory.Ok },
@@ -231,20 +230,23 @@ internal sealed class FakeGatewayTransport(MxGatewayClientOptions options) : IMx
     }
 
     /// <summary>
-    /// Records the query call and yields each enqueued snapshot.
+    /// Records the call and yields each enqueued snapshot as an active-alarm
+    /// feed message, then a snapshot-complete sentinel.
     /// </summary>
-    public async IAsyncEnumerable<ActiveAlarmSnapshot> QueryActiveAlarmsAsync(
-        QueryActiveAlarmsRequest request,
+    public async IAsyncEnumerable<AlarmFeedMessage> StreamAlarmsAsync(
+        StreamAlarmsRequest request,
         CallOptions callOptions)
     {
-        QueryActiveAlarmsCalls.Add((request, callOptions));
+        StreamAlarmsCalls.Add((request, callOptions));
 
         foreach (ActiveAlarmSnapshot snapshot in _activeAlarmSnapshots)
         {
             callOptions.CancellationToken.ThrowIfCancellationRequested();
             await Task.Yield();
-            yield return snapshot;
+            yield return new AlarmFeedMessage { ActiveAlarm = snapshot };
         }
+
+        yield return new AlarmFeedMessage { SnapshotComplete = true };
     }
 
     /// <summary>Enqueues an acknowledge reply.</summary>
@@ -253,7 +255,7 @@ internal sealed class FakeGatewayTransport(MxGatewayClientOptions options) : IMx
         _acknowledgeReplies.Enqueue(reply);
     }
 
-    /// <summary>Enqueues a snapshot to be yielded from QueryActiveAlarmsAsync.</summary>
+    /// <summary>Enqueues a snapshot yielded from StreamAlarmsAsync as an active-alarm message.</summary>
     public void AddActiveAlarmSnapshot(ActiveAlarmSnapshot snapshot)
     {
         _activeAlarmSnapshots.Add(snapshot);
diff --git a/clients/dotnet/MxGateway.Client.Tests/MxGatewayClientAlarmsTests.cs b/clients/dotnet/MxGateway.Client.Tests/MxGatewayClientAlarmsTests.cs
index 3423c2b..9e43b60 100644
--- a/clients/dotnet/MxGateway.Client.Tests/MxGatewayClientAlarmsTests.cs
+++ b/clients/dotnet/MxGateway.Client.Tests/MxGatewayClientAlarmsTests.cs
@@ -5,9 +5,9 @@ using MxGateway.Contracts.Proto;
 namespace MxGateway.Client.Tests;
 
 /// <summary>
-///     PR E.2 — pins the .NET SDK surface for the new alarm RPCs:
+///     Pins the .NET SDK surface for the alarm RPCs:
 ///     <see cref="MxGatewayClient.AcknowledgeAlarmAsync"/> and
-///     <see cref="MxGatewayClient.QueryActiveAlarmsAsync"/>.
+///     <see cref="MxGatewayClient.StreamAlarmsAsync"/>.
 /// </summary>
 public sealed class MxGatewayClientAlarmsTests
 {
@@ -17,7 +17,6 @@ public sealed class MxGatewayClientAlarmsTests
         FakeGatewayTransport transport = CreateTransport();
         transport.AddAcknowledgeReply(new AcknowledgeAlarmReply
         {
-            SessionId = "session-fixture",
             CorrelationId = "corr-1",
             ProtocolStatus = new ProtocolStatus { Code = ProtocolStatusCode.Ok },
             Status = new MxStatusProxy
@@ -31,7 +30,6 @@ public sealed class MxGatewayClientAlarmsTests
 
         AcknowledgeAlarmReply reply = await client.AcknowledgeAlarmAsync(new AcknowledgeAlarmRequest
         {
-            SessionId = "session-fixture",
             ClientCorrelationId = "corr-1",
             AlarmFullReference = "Tank01.Level.HiHi",
             Comment = "investigating",
@@ -64,7 +62,6 @@ public sealed class MxGatewayClientAlarmsTests
             client.AcknowledgeAlarmAsync(
                 new AcknowledgeAlarmRequest
                 {
-                    SessionId = "session-fixture",
                     AlarmFullReference = "Tank01.Level.HiHi",
                     Comment = string.Empty,
                     OperatorUser = "alice",
@@ -87,7 +84,6 @@ public sealed class MxGatewayClientAlarmsTests
         var ex = await Assert.ThrowsAsync<RpcException>(
             () => client.AcknowledgeAlarmAsync(new AcknowledgeAlarmRequest
             {
-                SessionId = "session-fixture",
                 AlarmFullReference = "Tank01.Level.HiHi",
                 Comment = string.Empty,
                 OperatorUser = "alice",
@@ -113,7 +109,6 @@ public sealed class MxGatewayClientAlarmsTests
         var ex = await Assert.ThrowsAsync<MxGatewayAuthenticationException>(
             () => client.AcknowledgeAlarmAsync(new AcknowledgeAlarmRequest
             {
-                SessionId = "session-fixture",
                 AlarmFullReference = "Tank01.Level.HiHi",
                 Comment = string.Empty,
                 OperatorUser = "alice",
@@ -122,50 +117,47 @@ public sealed class MxGatewayClientAlarmsTests
     }
 
     [Fact]
-    public async Task QueryActiveAlarmsAsync_StreamsEnqueuedSnapshots()
+    public async Task StreamAlarmsAsync_StreamsSnapshotThenSnapshotComplete()
     {
         FakeGatewayTransport transport = CreateTransport();
         transport.AddActiveAlarmSnapshot(MakeSnapshot("Tank01.Level.HiHi", AlarmConditionState.Active));
         transport.AddActiveAlarmSnapshot(MakeSnapshot("Tank02.Level.HiHi", AlarmConditionState.ActiveAcked));
         await using MxGatewayClient client = CreateClient(transport);
 
-        List<ActiveAlarmSnapshot> snapshots = [];
-        await foreach (ActiveAlarmSnapshot snapshot in client.QueryActiveAlarmsAsync(new QueryActiveAlarmsRequest
+        List<AlarmFeedMessage> messages = [];
+        await foreach (AlarmFeedMessage message in client.StreamAlarmsAsync(new StreamAlarmsRequest()))
         {
-            SessionId = "session-fixture",
-        }))
-        {
-            snapshots.Add(snapshot);
+            messages.Add(message);
         }
 
-        Assert.Equal(2, snapshots.Count);
-        Assert.Equal("Tank01.Level.HiHi", snapshots[0].AlarmFullReference);
-        Assert.Equal(AlarmConditionState.Active, snapshots[0].CurrentState);
-        Assert.Equal(AlarmConditionState.ActiveAcked, snapshots[1].CurrentState);
-        Assert.Single(transport.QueryActiveAlarmsCalls);
+        Assert.Equal(3, messages.Count);
+        Assert.Equal("Tank01.Level.HiHi", messages[0].ActiveAlarm.AlarmFullReference);
+        Assert.Equal(AlarmConditionState.Active, messages[0].ActiveAlarm.CurrentState);
+        Assert.Equal(AlarmConditionState.ActiveAcked, messages[1].ActiveAlarm.CurrentState);
+        Assert.True(messages[2].SnapshotComplete);
+        Assert.Single(transport.StreamAlarmsCalls);
     }
 
     [Fact]
-    public async Task QueryActiveAlarmsAsync_PassesFilterPrefix()
+    public async Task StreamAlarmsAsync_PassesFilterPrefix()
     {
         FakeGatewayTransport transport = CreateTransport();
         await using MxGatewayClient client = CreateClient(transport);
 
-        await foreach (ActiveAlarmSnapshot _ in client.QueryActiveAlarmsAsync(new QueryActiveAlarmsRequest
+        await foreach (AlarmFeedMessage _ in client.StreamAlarmsAsync(new StreamAlarmsRequest
         {
-            SessionId = "session-fixture",
             AlarmFilterPrefix = "Tank01.",
         }))
         {
-            // no snapshots enqueued; just verifying the request passes through
+            // only the snapshot-complete sentinel; verifying the request passes through
         }
 
-        var call = Assert.Single(transport.QueryActiveAlarmsCalls);
+        var call = Assert.Single(transport.StreamAlarmsCalls);
         Assert.Equal("Tank01.", call.Request.AlarmFilterPrefix);
     }
 
     [Fact]
-    public async Task QueryActiveAlarmsAsync_HonorsCancellationDuringEnumeration()
+    public async Task StreamAlarmsAsync_HonorsCancellationDuringEnumeration()
     {
         FakeGatewayTransport transport = CreateTransport();
         transport.AddActiveAlarmSnapshot(MakeSnapshot("Tank01.Level.HiHi", AlarmConditionState.Active));
@@ -175,8 +167,8 @@ public sealed class MxGatewayClientAlarmsTests
         using CancellationTokenSource cancellation = new();
         await Assert.ThrowsAsync<OperationCanceledException>(async () =>
         {
-            await foreach (ActiveAlarmSnapshot _ in client.QueryActiveAlarmsAsync(
-                new QueryActiveAlarmsRequest { SessionId = "session-fixture" },
+            await foreach (AlarmFeedMessage _ in client.StreamAlarmsAsync(
+                new StreamAlarmsRequest(),
                 cancellation.Token))
             {
                 cancellation.Cancel();
diff --git a/clients/dotnet/MxGateway.Client/GrpcMxGatewayClientTransport.cs b/clients/dotnet/MxGateway.Client/GrpcMxGatewayClientTransport.cs
index ef967da..7cfa56f 100644
--- a/clients/dotnet/MxGateway.Client/GrpcMxGatewayClientTransport.cs
+++ b/clients/dotnet/MxGateway.Client/GrpcMxGatewayClientTransport.cs
@@ -134,8 +134,8 @@ internal sealed class GrpcMxGatewayClientTransport(
     }
 
     /// <inheritdoc />
-    public async IAsyncEnumerable<ActiveAlarmSnapshot> QueryActiveAlarmsAsync(
-        QueryActiveAlarmsRequest request,
+    public async IAsyncEnumerable<AlarmFeedMessage> StreamAlarmsAsync(
+        StreamAlarmsRequest request,
         CallOptions callOptions,
         [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken = default)
     {
@@ -143,12 +143,12 @@ internal sealed class GrpcMxGatewayClientTransport(
             ? cancellationToken
             : callOptions.CancellationToken;
 
-        using AsyncServerStreamingCall<ActiveAlarmSnapshot> call = RawClient.QueryActiveAlarms(request, callOptions);
+        using AsyncServerStreamingCall<AlarmFeedMessage> call = RawClient.StreamAlarms(request, callOptions);
 
-        IAsyncStreamReader<ActiveAlarmSnapshot> responseStream = call.ResponseStream;
+        IAsyncStreamReader<AlarmFeedMessage> responseStream = call.ResponseStream;
         while (true)
         {
-            ActiveAlarmSnapshot? snapshot;
+            AlarmFeedMessage? message;
             try
             {
                 if (!await responseStream.MoveNext(effectiveCancellationToken).ConfigureAwait(false))
@@ -156,22 +156,22 @@ internal sealed class GrpcMxGatewayClientTransport(
                     break;
                 }
 
-                snapshot = responseStream.Current;
+                message = responseStream.Current;
             }
             catch (RpcException exception)
             {
                 throw RpcExceptionMapper.Map(exception, effectiveCancellationToken);
             }
 
-            yield return snapshot;
+            yield return message;
         }
     }
 
     /// <inheritdoc />
-    IAsyncEnumerable<ActiveAlarmSnapshot> IMxGatewayClientTransport.QueryActiveAlarmsAsync(
-        QueryActiveAlarmsRequest request,
+    IAsyncEnumerable<AlarmFeedMessage> IMxGatewayClientTransport.StreamAlarmsAsync(
+        StreamAlarmsRequest request,
         CallOptions callOptions)
     {
-        return QueryActiveAlarmsAsync(request, callOptions);
+        return StreamAlarmsAsync(request, callOptions);
     }
 }
diff --git a/clients/dotnet/MxGateway.Client/IMxGatewayClientTransport.cs b/clients/dotnet/MxGateway.Client/IMxGatewayClientTransport.cs
index 26e25fc..bed8f2e 100644
--- a/clients/dotnet/MxGateway.Client/IMxGatewayClientTransport.cs
+++ b/clients/dotnet/MxGateway.Client/IMxGatewayClientTransport.cs
@@ -66,13 +66,13 @@ internal interface IMxGatewayClientTransport
         CallOptions callOptions);
 
     /// <summary>
-    /// Streams a snapshot of all alarms currently in Active or ActiveAcked state — the
-    /// ConditionRefresh equivalent for the gateway.
+    /// Attaches to the gateway's central alarm feed — the current active-alarm
+    /// snapshot followed by live transitions.
     /// </summary>
-    /// <param name="request">The query request, optionally scoped by alarm-reference prefix.</param>
+    /// <param name="request">The stream request, optionally scoped by alarm-reference prefix.</param>
     /// <param name="callOptions">gRPC call options.</param>
-    /// <returns>An async enumerable of active-alarm snapshots.</returns>
-    IAsyncEnumerable<ActiveAlarmSnapshot> QueryActiveAlarmsAsync(
-        QueryActiveAlarmsRequest request,
+    /// <returns>An async enumerable of alarm feed messages.</returns>
+    IAsyncEnumerable<AlarmFeedMessage> StreamAlarmsAsync(
+        StreamAlarmsRequest request,
         CallOptions callOptions);
 }
diff --git a/clients/dotnet/MxGateway.Client/MxGatewayClient.cs b/clients/dotnet/MxGateway.Client/MxGatewayClient.cs
index f46b7ed..3d390f6 100644
--- a/clients/dotnet/MxGateway.Client/MxGatewayClient.cs
+++ b/clients/dotnet/MxGateway.Client/MxGatewayClient.cs
@@ -205,24 +205,25 @@ public sealed class MxGatewayClient : IAsyncDisposable
     }
 
     /// <summary>
-    /// Streams a snapshot of all alarms currently Active or ActiveAcked — the gateway's
-    /// ConditionRefresh equivalent. Used after reconnect to seed the local Part 9 state
-    /// machine, or to reconcile alarms that may have been missed during a transport
-    /// blip. Optionally scoped by alarm-reference prefix
-    /// (<see cref="QueryActiveAlarmsRequest.AlarmFilterPrefix"/>) so a partial refresh
-    /// can target an equipment sub-tree.
+    /// Attaches to the gateway's central alarm feed. The stream opens with one
+    /// <see cref="AlarmFeedMessage"/> per currently-active alarm (the
+    /// ConditionRefresh snapshot), then a single <c>snapshot_complete</c>, then a
+    /// <c>transition</c> for every subsequent raise / acknowledge / clear. Served
+    /// by the gateway's always-on alarm monitor — no worker session is opened, so
+    /// any number of clients may attach. Optionally scoped by alarm-reference
+    /// prefix (<see cref="StreamAlarmsRequest.AlarmFilterPrefix"/>).
     /// </summary>
-    /// <param name="request">The query request, optionally scoped by alarm-reference prefix.</param>
+    /// <param name="request">The stream request, optionally scoped by alarm-reference prefix.</param>
     /// <param name="cancellationToken">Cancellation token for the stream.</param>
-    /// <returns>An async enumerable of active-alarm snapshots.</returns>
-    public IAsyncEnumerable<ActiveAlarmSnapshot> QueryActiveAlarmsAsync(
-        QueryActiveAlarmsRequest request,
+    /// <returns>An async enumerable of alarm feed messages.</returns>
+    public IAsyncEnumerable<AlarmFeedMessage> StreamAlarmsAsync(
+        StreamAlarmsRequest request,
         CancellationToken cancellationToken = default)
     {
         ArgumentNullException.ThrowIfNull(request);
         ThrowIfDisposed();
 
-        return _transport.QueryActiveAlarmsAsync(request, CreateStreamCallOptions(cancellationToken));
+        return _transport.StreamAlarmsAsync(request, CreateStreamCallOptions(cancellationToken));
     }
 
     /// <summary>