diff --git a/src/ScadaLink.Communication/Actors/SiteCommunicationActor.cs b/src/ScadaLink.Communication/Actors/SiteCommunicationActor.cs
index 2040268..1bcfd2d 100644
--- a/src/ScadaLink.Communication/Actors/SiteCommunicationActor.cs
+++ b/src/ScadaLink.Communication/Actors/SiteCommunicationActor.cs
@@ -5,6 +5,7 @@ using ScadaLink.Commons.Messages.Artifacts;
 using ScadaLink.Commons.Messages.DebugView;
 using ScadaLink.Commons.Messages.Deployment;
 using ScadaLink.Commons.Messages.Health;
+using ScadaLink.Commons.Messages.InboundApi;
 using ScadaLink.Commons.Messages.Integration;
 using ScadaLink.Commons.Messages.Lifecycle;
 using ScadaLink.Commons.Messages.RemoteQuery;
@@ -107,6 +108,9 @@ public class SiteCommunicationActor : ReceiveActor, IWithTimers
         // Pattern 6a: Debug Snapshot (one-shot) — forward to Deployment Manager
         Receive<DebugSnapshotRequest>(msg => _deploymentManagerProxy.Forward(msg));
 
+        // Inbound API Route.To().Call() — forward to Deployment Manager for instance routing
+        Receive<RouteToCallRequest>(msg => _deploymentManagerProxy.Forward(msg));
+
         // Pattern 7: Remote Queries
         Receive<EventLogQueryRequest>(msg =>
         {
diff --git a/src/ScadaLink.Host/Program.cs b/src/ScadaLink.Host/Program.cs
index 98ca6ec..cdedc71 100644
--- a/src/ScadaLink.Host/Program.cs
+++ b/src/ScadaLink.Host/Program.cs
@@ -129,6 +129,19 @@ try
         app.MapStaticAssets();
         app.MapCentralUI<ScadaLink.Host.Components.App>();
         app.MapInboundAPI();
+
+        // Compile and register all Inbound API method scripts at startup
+        using (var scope = app.Services.CreateScope())
+        {
+            var apiRepo = scope.ServiceProvider.GetRequiredService<ScadaLink.Commons.Interfaces.Repositories.IInboundApiRepository>();
+            var executor = app.Services.GetRequiredService<ScadaLink.InboundAPI.InboundScriptExecutor>();
+            var methods = await apiRepo.GetAllApiMethodsAsync();
+            foreach (var method in methods)
+            {
+                executor.CompileAndRegister(method);
+            }
+        }
+
         await app.RunAsync();
     }
     else if (nodeRole.Equals("Site", StringComparison.OrdinalIgnoreCase))
diff --git a/src/ScadaLink.InboundAPI/InboundScriptExecutor.cs b/src/ScadaLink.InboundAPI/InboundScriptExecutor.cs
index 881ebc5..fd0cdc8 100644
--- a/src/ScadaLink.InboundAPI/InboundScriptExecutor.cs
+++ b/src/ScadaLink.InboundAPI/InboundScriptExecutor.cs
@@ -1,4 +1,6 @@
 using System.Text.Json;
+using Microsoft.CodeAnalysis.CSharp.Scripting;
+using Microsoft.CodeAnalysis.Scripting;
 using Microsoft.Extensions.Logging;
 using ScadaLink.Commons.Entities.InboundApi;
 
@@ -6,11 +8,7 @@ namespace ScadaLink.InboundAPI;
 
 /// <summary>
 /// WP-3: Executes the C# script associated with an inbound API method.
-/// The script receives input parameters and a route helper, and returns a result
-/// that is serialized as the JSON response.
-///
-/// In a full implementation this would use Roslyn scripting. For now, scripts
-/// are a simple dispatch table so the rest of the pipeline can be tested end-to-end.
+/// Compiles method scripts via Roslyn and caches compiled delegates.
 /// </summary>
 public class InboundScriptExecutor
 {
@@ -24,13 +22,73 @@ public class InboundScriptExecutor
 
     /// <summary>
     /// Registers a compiled script handler for a method name.
-    /// In production, this would be called after Roslyn compilation of the method's Script property.
     /// </summary>
     public void RegisterHandler(string methodName, Func<InboundScriptContext, Task<object?>> handler)
     {
         _scriptHandlers[methodName] = handler;
     }
 
+    /// <summary>
+    /// Compiles and registers a single API method script.
+    /// </summary>
+    public bool CompileAndRegister(ApiMethod method)
+    {
+        if (string.IsNullOrWhiteSpace(method.Script))
+        {
+            _logger.LogWarning("API method {Method} has no script code", method.Name);
+            return false;
+        }
+
+        try
+        {
+            var scriptOptions = ScriptOptions.Default
+                .WithReferences(
+                    typeof(object).Assembly,
+                    typeof(Enumerable).Assembly,
+                    typeof(Dictionary<,>).Assembly,
+                    typeof(RouteHelper).Assembly,
+                    typeof(Microsoft.CSharp.RuntimeBinder.CSharpArgumentInfo).Assembly)
+                .WithImports(
+                    "System",
+                    "System.Collections.Generic",
+                    "System.Linq",
+                    "System.Threading.Tasks");
+
+            var compiled = CSharpScript.Create<object?>(
+                method.Script,
+                scriptOptions,
+                globalsType: typeof(InboundScriptContext));
+
+            var diagnostics = compiled.Compile();
+            var errors = diagnostics
+                .Where(d => d.Severity == Microsoft.CodeAnalysis.DiagnosticSeverity.Error)
+                .Select(d => d.GetMessage())
+                .ToList();
+
+            if (errors.Count > 0)
+            {
+                _logger.LogWarning(
+                    "API method {Method} script compilation failed: {Errors}",
+                    method.Name, string.Join("; ", errors));
+                return false;
+            }
+
+            _scriptHandlers[method.Name] = async ctx =>
+            {
+                var state = await compiled.RunAsync(ctx, ctx.CancellationToken);
+                return state.ReturnValue;
+            };
+
+            _logger.LogInformation("API method {Method} script compiled and registered", method.Name);
+            return true;
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Failed to compile API method {Method} script", method.Name);
+            return false;
+        }
+    }
+
     /// <summary>
     /// Executes the script for the given method with the provided context.
     /// </summary>
diff --git a/src/ScadaLink.InboundAPI/ScadaLink.InboundAPI.csproj b/src/ScadaLink.InboundAPI/ScadaLink.InboundAPI.csproj
index 59f3185..c75e249 100644
--- a/src/ScadaLink.InboundAPI/ScadaLink.InboundAPI.csproj
+++ b/src/ScadaLink.InboundAPI/ScadaLink.InboundAPI.csproj
@@ -20,4 +20,8 @@
     <InternalsVisibleTo Include="ScadaLink.InboundAPI.Tests" />
   </ItemGroup>
 
+  <ItemGroup>
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp.Scripting" Version="5.0.0" />
+  </ItemGroup>
+
 </Project>
diff --git a/src/ScadaLink.SiteRuntime/Actors/DeploymentManagerActor.cs b/src/ScadaLink.SiteRuntime/Actors/DeploymentManagerActor.cs
index 52f81e4..9de0b17 100644
--- a/src/ScadaLink.SiteRuntime/Actors/DeploymentManagerActor.cs
+++ b/src/ScadaLink.SiteRuntime/Actors/DeploymentManagerActor.cs
@@ -3,7 +3,9 @@ using Microsoft.Extensions.Logging;
 using ScadaLink.Commons.Messages.Artifacts;
 using ScadaLink.Commons.Messages.DebugView;
 using ScadaLink.Commons.Messages.Deployment;
+using ScadaLink.Commons.Messages.InboundApi;
 using ScadaLink.Commons.Messages.Lifecycle;
+using ScadaLink.Commons.Messages.ScriptExecution;
 using ScadaLink.Commons.Types.Enums;
 using ScadaLink.HealthMonitoring;
 using ScadaLink.SiteRuntime.Messages;
@@ -77,6 +79,9 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
         Receive<UnsubscribeDebugViewRequest>(RouteDebugViewUnsubscribe);
         Receive<DebugSnapshotRequest>(RouteDebugSnapshot);
 
+        // Inbound API Route.To().Call() — route to Instance Actors
+        Receive<RouteToCallRequest>(RouteInboundApiCall);
+
         // Internal startup messages
         Receive<StartupConfigsLoaded>(HandleStartupConfigsLoaded);
         Receive<StartNextBatch>(HandleStartNextBatch);
@@ -486,6 +491,41 @@ public class DeploymentManagerActor : ReceiveActor, IWithTimers
         }
     }
 
+    // ── Inbound API routing ──
+
+    private void RouteInboundApiCall(RouteToCallRequest request)
+    {
+        if (_instanceActors.TryGetValue(request.InstanceUniqueName, out var instanceActor))
+        {
+            // Convert to ScriptCallRequest and Ask the Instance Actor
+            var scriptCall = new ScriptCallRequest(
+                request.ScriptName, request.Parameters, 0, request.CorrelationId);
+            var sender = Sender;
+            instanceActor.Ask<ScriptCallResult>(scriptCall, TimeSpan.FromSeconds(30))
+                .ContinueWith(t =>
+                {
+                    if (t.IsCompletedSuccessfully)
+                    {
+                        var result = t.Result;
+                        return new RouteToCallResponse(
+                            request.CorrelationId, result.Success, result.ReturnValue,
+                            result.ErrorMessage, DateTimeOffset.UtcNow);
+                    }
+                    return new RouteToCallResponse(
+                        request.CorrelationId, false, null,
+                        t.Exception?.GetBaseException().Message ?? "Script call timed out",
+                        DateTimeOffset.UtcNow);
+                }).PipeTo(sender);
+        }
+        else
+        {
+            Sender.Tell(new RouteToCallResponse(
+                request.CorrelationId, false, null,
+                $"Instance '{request.InstanceUniqueName}' not found on this site.",
+                DateTimeOffset.UtcNow));
+        }
+    }
+
     /// <summary>
     /// WP-33: Handles system-wide artifact deployment (shared scripts, external systems, etc.).
     /// Persists artifacts to SiteStorageService and recompiles shared scripts.