diff --git a/src/ZB.MOM.WW.ScadaBridge.Commons/Messages/InboundApi/RouteToInstanceRequest.cs b/src/ZB.MOM.WW.ScadaBridge.Commons/Messages/InboundApi/RouteToInstanceRequest.cs
index f308a732..0798bbc5 100644
--- a/src/ZB.MOM.WW.ScadaBridge.Commons/Messages/InboundApi/RouteToInstanceRequest.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.Commons/Messages/InboundApi/RouteToInstanceRequest.cs
@@ -83,3 +83,46 @@ public record RouteToSetAttributesResponse(
     bool Success,
     string? ErrorMessage,
     DateTimeOffset Timestamp);
+
+/// <summary>
+/// Request to block until a remote instance attribute reaches a target value
+/// (spec §6 — <c>Route.To("inst").WaitForAttribute(name, targetValue, timeout)</c>).
+/// Value-equality ONLY across the wire: <see cref="TargetValueEncoded"/> carries the
+/// canonical <c>AttributeValueCodec</c>-encoded target; there is no predicate and no
+/// quality flag in the comparison. The site evaluates equality and either matches or
+/// times out.
+/// </summary>
+/// <param name="ParentExecutionId">
+/// Audit Log #23 (ParentExecutionId): mirrors <see cref="RouteToCallRequest.ParentExecutionId"/>.
+/// For an inbound-API-routed wait this is the inbound request's per-request execution id;
+/// future site-side audit emission for routed waits can stamp it as <c>ParentExecutionId</c>
+/// so the inbound→site execution-tree link survives the wait path. Additive trailing
+/// member — null for the Central UI sandbox path or for callers built before the field existed.
+/// </param>
+public record RouteToWaitForAttributeRequest(
+    string CorrelationId,
+    string InstanceUniqueName,
+    string AttributeName,
+    string? TargetValueEncoded,
+    TimeSpan Timeout,
+    DateTimeOffset Timestamp,
+    Guid? ParentExecutionId = null);
+
+/// <summary>
+/// Response from a remote attribute wait. <see cref="Success"/>/<see cref="ErrorMessage"/>
+/// convey the routing-level outcome (e.g. instance-not-found); <see cref="Matched"/>,
+/// <see cref="TimedOut"/>, <see cref="Value"/>, and <see cref="Quality"/> convey the wait
+/// outcome itself. When <see cref="Success"/> is <c>true</c>, exactly one of
+/// <see cref="Matched"/>/<see cref="TimedOut"/> holds: <see cref="Matched"/> means the
+/// attribute reached the target value (with <see cref="Value"/>/<see cref="Quality"/>
+/// captured at the match), <see cref="TimedOut"/> means the deadline elapsed first.
+/// </summary>
+public record RouteToWaitForAttributeResponse(
+    string CorrelationId,
+    bool Matched,
+    object? Value,
+    string? Quality,
+    bool TimedOut,
+    bool Success,
+    string? ErrorMessage,
+    DateTimeOffset Timestamp);
diff --git a/src/ZB.MOM.WW.ScadaBridge.Communication/CommunicationService.cs b/src/ZB.MOM.WW.ScadaBridge.Communication/CommunicationService.cs
index 7cec3a3e..3b866e35 100644
--- a/src/ZB.MOM.WW.ScadaBridge.Communication/CommunicationService.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.Communication/CommunicationService.cs
@@ -445,6 +445,25 @@ public class CommunicationService
             envelope, _options.IntegrationTimeout, cancellationToken);
     }
 
+    /// <summary>
+    /// Routes an inbound API wait-for-attribute request to a site (spec §6).
+    /// </summary>
+    /// <param name="siteId">The target site identifier.</param>
+    /// <param name="request">The wait-for-attribute route request.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>The wait-for-attribute route response.</returns>
+    public async Task<RouteToWaitForAttributeResponse> RouteToWaitForAttributeAsync(
+        string siteId, RouteToWaitForAttributeRequest request, CancellationToken cancellationToken = default)
+    {
+        var envelope = new SiteEnvelope(siteId, request);
+        // A wait legitimately blocks up to request.Timeout on the site, so the cluster
+        // Ask must be bounded by the WAIT deadline (plus integration-timeout slack for
+        // the round trip), not the generic IntegrationTimeout used by the other routes.
+        var askTimeout = request.Timeout + _options.IntegrationTimeout;
+        return await GetActor().Ask<RouteToWaitForAttributeResponse>(
+            envelope, askTimeout, cancellationToken);
+    }
+
     // ── Notification Outbox (central-local actor — Asked directly, no SiteEnvelope) ──
 
     /// <summary>
diff --git a/src/ZB.MOM.WW.ScadaBridge.InboundAPI/CommunicationServiceInstanceRouter.cs b/src/ZB.MOM.WW.ScadaBridge.InboundAPI/CommunicationServiceInstanceRouter.cs
index 01e001e1..d306ec33 100644
--- a/src/ZB.MOM.WW.ScadaBridge.InboundAPI/CommunicationServiceInstanceRouter.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.InboundAPI/CommunicationServiceInstanceRouter.cs
@@ -35,4 +35,9 @@ public sealed class CommunicationServiceInstanceRouter : IInstanceRouter
     public Task<RouteToSetAttributesResponse> RouteToSetAttributesAsync(
         string siteId, RouteToSetAttributesRequest request, CancellationToken cancellationToken) =>
         _communicationService.RouteToSetAttributesAsync(siteId, request, cancellationToken);
+
+    /// <inheritdoc />
+    public Task<RouteToWaitForAttributeResponse> RouteToWaitForAttributeAsync(
+        string siteId, RouteToWaitForAttributeRequest request, CancellationToken cancellationToken) =>
+        _communicationService.RouteToWaitForAttributeAsync(siteId, request, cancellationToken);
 }
diff --git a/src/ZB.MOM.WW.ScadaBridge.InboundAPI/IInstanceRouter.cs b/src/ZB.MOM.WW.ScadaBridge.InboundAPI/IInstanceRouter.cs
index 1d08d123..65a00535 100644
--- a/src/ZB.MOM.WW.ScadaBridge.InboundAPI/IInstanceRouter.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.InboundAPI/IInstanceRouter.cs
@@ -34,4 +34,12 @@ public interface IInstanceRouter
     /// <returns>A task that resolves to the set-attributes response from the target site.</returns>
     Task<RouteToSetAttributesResponse> RouteToSetAttributesAsync(
         string siteId, RouteToSetAttributesRequest request, CancellationToken cancellationToken);
+
+    /// <summary>Routes a wait-for-attribute request to the specified site (spec §6).</summary>
+    /// <param name="siteId">Target site identifier.</param>
+    /// <param name="request">The wait-for-attribute request to route (value-equality only).</param>
+    /// <param name="cancellationToken">Cancellation token for the routed call.</param>
+    /// <returns>A task that resolves to the wait-for-attribute response from the target site.</returns>
+    Task<RouteToWaitForAttributeResponse> RouteToWaitForAttributeAsync(
+        string siteId, RouteToWaitForAttributeRequest request, CancellationToken cancellationToken);
 }
diff --git a/src/ZB.MOM.WW.ScadaBridge.InboundAPI/RouteHelper.cs b/src/ZB.MOM.WW.ScadaBridge.InboundAPI/RouteHelper.cs
index 76c02a97..b335f232 100644
--- a/src/ZB.MOM.WW.ScadaBridge.InboundAPI/RouteHelper.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.InboundAPI/RouteHelper.cs
@@ -205,6 +205,47 @@ public class RouteTarget
         return response.Values;
     }
 
+    /// <summary>
+    /// Blocks until a remote instance attribute reaches <paramref name="targetValue"/>
+    /// or <paramref name="timeout"/> elapses (spec §6). Value-equality ONLY across the
+    /// wire: the target is canonically encoded via <see cref="AttributeValueCodec"/> and
+    /// the site evaluates equality — there is no predicate and no quality flag in the
+    /// comparison.
+    /// </summary>
+    /// <param name="attributeName">Name of the attribute to wait on.</param>
+    /// <param name="targetValue">Target value the attribute must equal for the wait to match.</param>
+    /// <param name="timeout">Maximum time to wait for the attribute to reach the target value.</param>
+    /// <param name="cancellationToken">Optional cancellation token; defaults to the method deadline.</param>
+    /// <returns>A task that resolves to <c>true</c> if the attribute reached the target value, <c>false</c> if the wait timed out.</returns>
+    public async Task<bool> WaitForAttribute(
+        string attributeName,
+        object? targetValue,
+        TimeSpan timeout,
+        CancellationToken cancellationToken = default)
+    {
+        var token = Effective(cancellationToken);
+        var siteId = await ResolveSiteAsync(token);
+
+        // Audit Log #23 (ParentExecutionId): mirrors the Call path — stamp the
+        // spawning inbound request's ExecutionId so future site-side audit
+        // emission for routed waits can record this wait's parent. CorrelationId
+        // is the per-operation lifecycle id, freshly minted per routed wait.
+        var request = new RouteToWaitForAttributeRequest(
+            Guid.NewGuid().ToString(), _instanceCode, attributeName,
+            AttributeValueCodec.Encode(targetValue), timeout, DateTimeOffset.UtcNow,
+            _parentExecutionId);
+
+        var response = await _instanceRouter.RouteToWaitForAttributeAsync(siteId, request, token);
+
+        if (!response.Success)
+        {
+            throw new InvalidOperationException(
+                response.ErrorMessage ?? "Remote attribute wait failed");
+        }
+
+        return response.Matched;
+    }
+
     /// <summary>
     /// Sets a single attribute value on the remote instance.
     /// </summary>
diff --git a/tests/ZB.MOM.WW.ScadaBridge.AuditLog.Tests/Integration/ParentExecutionIdCorrelationTests.cs b/tests/ZB.MOM.WW.ScadaBridge.AuditLog.Tests/Integration/ParentExecutionIdCorrelationTests.cs
index 99459613..1b21ffec 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.AuditLog.Tests/Integration/ParentExecutionIdCorrelationTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.AuditLog.Tests/Integration/ParentExecutionIdCorrelationTests.cs
@@ -623,5 +623,11 @@ public class ParentExecutionIdCorrelationTests : TestKit, IClassFixture<MsSqlMig
         public Task<RouteToSetAttributesResponse> RouteToSetAttributesAsync(
             string siteId, RouteToSetAttributesRequest request, CancellationToken cancellationToken)
             => throw new NotSupportedException();
+
+        // WaitForAttribute is not part of this fixture's routed-Call audit scenario;
+        // mirror the other non-Call methods (unexercised here).
+        public Task<RouteToWaitForAttributeResponse> RouteToWaitForAttributeAsync(
+            string siteId, RouteToWaitForAttributeRequest request, CancellationToken cancellationToken)
+            => throw new NotSupportedException();
     }
 }
diff --git a/tests/ZB.MOM.WW.ScadaBridge.InboundAPI.Tests/RouteHelperTests.cs b/tests/ZB.MOM.WW.ScadaBridge.InboundAPI.Tests/RouteHelperTests.cs
index 4abcf17a..a812f205 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.InboundAPI.Tests/RouteHelperTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.InboundAPI.Tests/RouteHelperTests.cs
@@ -1,6 +1,7 @@
 using NSubstitute;
 using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Services;
 using ZB.MOM.WW.ScadaBridge.Commons.Messages.InboundApi;
+using ZB.MOM.WW.ScadaBridge.Commons.Types;
 
 namespace ZB.MOM.WW.ScadaBridge.InboundAPI.Tests;
 
@@ -139,6 +140,116 @@ public class RouteHelperTests
         Assert.Equal("read failed", ex.Message);
     }
 
+    // --- WaitForAttribute (spec §6) ---
+
+    [Fact]
+    public async Task WaitForAttribute_Matched_ReturnsTrue()
+    {
+        SiteResolves("inst-1", "SiteA");
+        _router.RouteToWaitForAttributeAsync("SiteA", Arg.Any<RouteToWaitForAttributeRequest>(), Arg.Any<CancellationToken>())
+            .Returns(ci => new RouteToWaitForAttributeResponse(
+                ((RouteToWaitForAttributeRequest)ci[1]).CorrelationId,
+                Matched: true, Value: true, Quality: "Good", TimedOut: false,
+                Success: true, ErrorMessage: null, DateTimeOffset.UtcNow));
+
+        var matched = await CreateHelper().To("inst-1")
+            .WaitForAttribute("Flag", true, TimeSpan.FromSeconds(30));
+
+        Assert.True(matched);
+    }
+
+    [Fact]
+    public async Task WaitForAttribute_TimedOut_ReturnsFalse()
+    {
+        SiteResolves("inst-1", "SiteA");
+        _router.RouteToWaitForAttributeAsync("SiteA", Arg.Any<RouteToWaitForAttributeRequest>(), Arg.Any<CancellationToken>())
+            .Returns(ci => new RouteToWaitForAttributeResponse(
+                ((RouteToWaitForAttributeRequest)ci[1]).CorrelationId,
+                Matched: false, Value: null, Quality: null, TimedOut: true,
+                Success: true, ErrorMessage: null, DateTimeOffset.UtcNow));
+
+        var matched = await CreateHelper().To("inst-1")
+            .WaitForAttribute("Flag", true, TimeSpan.FromSeconds(30));
+
+        Assert.False(matched);
+    }
+
+    [Fact]
+    public async Task WaitForAttribute_RoutingFailure_ThrowsInvalidOperationException()
+    {
+        // Success=false is a routing-level outcome (e.g. instance not found on the
+        // site), distinct from the wait outcome (Matched/TimedOut).
+        SiteResolves("inst-1", "SiteA");
+        _router.RouteToWaitForAttributeAsync("SiteA", Arg.Any<RouteToWaitForAttributeRequest>(), Arg.Any<CancellationToken>())
+            .Returns(ci => new RouteToWaitForAttributeResponse(
+                ((RouteToWaitForAttributeRequest)ci[1]).CorrelationId,
+                Matched: false, Value: null, Quality: null, TimedOut: false,
+                Success: false, ErrorMessage: "instance not found", DateTimeOffset.UtcNow));
+
+        var ex = await Assert.ThrowsAsync<InvalidOperationException>(
+            () => CreateHelper().To("inst-1").WaitForAttribute("Flag", true, TimeSpan.FromSeconds(30)));
+        Assert.Equal("instance not found", ex.Message);
+    }
+
+    [Fact]
+    public async Task WaitForAttribute_EncodesTargetValue_OnRequest()
+    {
+        // Value-equality only across the wire: the target value is encoded via the
+        // canonical AttributeValueCodec, identical to how attribute values travel.
+        SiteResolves("inst-1", "SiteA");
+        RouteToWaitForAttributeRequest? captured = null;
+        _router.RouteToWaitForAttributeAsync("SiteA", Arg.Do<RouteToWaitForAttributeRequest>(r => captured = r), Arg.Any<CancellationToken>())
+            .Returns(ci => new RouteToWaitForAttributeResponse(
+                ((RouteToWaitForAttributeRequest)ci[1]).CorrelationId,
+                Matched: true, Value: true, Quality: "Good", TimedOut: false,
+                Success: true, ErrorMessage: null, DateTimeOffset.UtcNow));
+
+        await CreateHelper().To("inst-1").WaitForAttribute("Flag", true, TimeSpan.FromSeconds(30));
+
+        Assert.NotNull(captured);
+        Assert.Equal("Flag", captured!.AttributeName);
+        Assert.Equal(TimeSpan.FromSeconds(30), captured.Timeout);
+        Assert.Equal(AttributeValueCodec.Encode(true), captured.TargetValueEncoded);
+        Assert.True(Guid.TryParse(captured.CorrelationId, out _));
+    }
+
+    [Fact]
+    public async Task WaitForAttribute_WithNoExplicitToken_InheritsMethodDeadlineToken()
+    {
+        SiteResolves("inst-1", "SiteA");
+        using var deadline = new CancellationTokenSource();
+        CancellationToken seen = default;
+        _router.RouteToWaitForAttributeAsync("SiteA", Arg.Any<RouteToWaitForAttributeRequest>(), Arg.Do<CancellationToken>(t => seen = t))
+            .Returns(ci => new RouteToWaitForAttributeResponse(
+                ((RouteToWaitForAttributeRequest)ci[1]).CorrelationId,
+                Matched: false, Value: null, Quality: null, TimedOut: true,
+                Success: true, ErrorMessage: null, DateTimeOffset.UtcNow));
+
+        var bound = CreateHelper().WithDeadline(deadline.Token);
+        await bound.To("inst-1").WaitForAttribute("Flag", true, TimeSpan.FromSeconds(30));
+
+        Assert.Equal(deadline.Token, seen);
+    }
+
+    [Fact]
+    public async Task WaitForAttribute_WithParentExecutionId_CarriesItOnRequest()
+    {
+        SiteResolves("inst-1", "SiteA");
+        var inboundExecutionId = Guid.NewGuid();
+        RouteToWaitForAttributeRequest? captured = null;
+        _router.RouteToWaitForAttributeAsync("SiteA", Arg.Do<RouteToWaitForAttributeRequest>(r => captured = r), Arg.Any<CancellationToken>())
+            .Returns(ci => new RouteToWaitForAttributeResponse(
+                ((RouteToWaitForAttributeRequest)ci[1]).CorrelationId,
+                Matched: true, Value: true, Quality: "Good", TimedOut: false,
+                Success: true, ErrorMessage: null, DateTimeOffset.UtcNow));
+
+        var bound = CreateHelper().WithParentExecutionId(inboundExecutionId);
+        await bound.To("inst-1").WaitForAttribute("Flag", true, TimeSpan.FromSeconds(30));
+
+        Assert.NotNull(captured);
+        Assert.Equal(inboundExecutionId, captured!.ParentExecutionId);
+    }
+
     // --- SetAttribute(s) ---
 
     [Fact]