diff --git a/src/Abstractions/Entities/EntityInstanceId.cs b/src/Abstractions/Entities/EntityInstanceId.cs
index d0f18a41a..52712a24a 100644
--- a/src/Abstractions/Entities/EntityInstanceId.cs
+++ b/src/Abstractions/Entities/EntityInstanceId.cs
@@ -1,15 +1,80 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
 namespace Microsoft.DurableTask.Entities;
 
 /// <summary>
 /// Represents the ID of an entity.
 /// </summary>
-/// <param name="Name">The name of the entity.</param>
-/// <param name="Key">The key for this entity.</param>
-public readonly record struct EntityInstanceId(string Name, string Key)
+[JsonConverter(typeof(EntityInstanceId.JsonConverter))]
+public readonly record struct EntityInstanceId
 {
+    /// <summary>
+    /// Initializes a new instance of the <see cref="EntityInstanceId"/> class.
+    /// </summary>
+    /// <param name="name">The entity name.</param>
+    /// <param name="key">The entity key.</param>
+    public EntityInstanceId(string name, string key)
+    {
+        Check.NotNullOrEmpty(name);
+        if (name.Contains('@'))
+        {
+            throw new ArgumentException("entity names may not contain `@` characters.", nameof(name));
+        }
+
+        Check.NotNull(key);
+        this.Name = name.ToLowerInvariant();
+        this.Key = key;
+    }
+
+    /// <summary>
+    /// Gets the entity name. Entity names are normalized to lower case.
+    /// </summary>
+    public string Name { get; }
+
+    /// <summary>
+    /// Gets the entity key.
+    /// </summary>
+    public string Key { get; }
+
+    /// <summary>
+    /// Constructs a <see cref="EntityInstanceId"/> from a string containing the instance ID.
+    /// </summary>
+    /// <param name="instanceId">The string representation of the entity ID.</param>
+    /// <returns>the constructed entity instance ID.</returns>
+    public static EntityInstanceId FromString(string instanceId)
+    {
+        Check.NotNullOrEmpty(instanceId);
+        var pos = instanceId.IndexOf('@', 1);
+        if (pos <= 0 || instanceId[0] != '@')
+        {
+            throw new ArgumentException($"Instance ID '{instanceId}' is not a valid entity ID.", nameof(instanceId));
+        }
+
+        var entityName = instanceId.Substring(1, pos - 1);
+        var entityKey = instanceId.Substring(pos + 1);
+        return new EntityInstanceId(entityName, entityKey);
+    }
+
     /// <inheritdoc/>
     public override string ToString() => $"@{this.Name}@{this.Key}";
+
+    /// <summary>
+    /// We override the default json conversion so we can use a more compact string representation for entity instance ids.
+    /// </summary>
+    class JsonConverter : JsonConverter<EntityInstanceId>
+    {
+        public override EntityInstanceId Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        {
+            return EntityInstanceId.FromString(reader.GetString()!);
+        }
+
+        public override void Write(Utf8JsonWriter writer, EntityInstanceId value, JsonSerializerOptions options)
+        {
+            writer.WriteStringValue(value.ToString()!);
+        }
+    }
 }
diff --git a/src/Client/Core/DurableTaskClientOptions.cs b/src/Client/Core/DurableTaskClientOptions.cs
index 1c84eb949..142be7e52 100644
--- a/src/Client/Core/DurableTaskClientOptions.cs
+++ b/src/Client/Core/DurableTaskClientOptions.cs
@@ -46,6 +46,12 @@ public DataConverter DataConverter
         }
     }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether this client should support entities. If true, all instance ids starting with '@' are reserved for entities,
+    /// and validation checks are performed where appropriate.
+    /// </summary>
+    public bool EnableEntitySupport { get; set; }
+
     /// <summary>
     /// Gets a value indicating whether <see cref="DataConverter" /> was explicitly set or not.
     /// </summary>
@@ -67,6 +73,7 @@ internal void ApplyTo(DurableTaskClientOptions other)
         {
             // Make sure to keep this up to date as values are added.
             other.DataConverter = this.DataConverter;
+            other.EnableEntitySupport = this.EnableEntitySupport;
         }
     }
 }
diff --git a/src/Client/Core/Entities/EntityQuery.cs b/src/Client/Core/Entities/EntityQuery.cs
index 15ef7a644..a356ebdef 100644
--- a/src/Client/Core/Entities/EntityQuery.cs
+++ b/src/Client/Core/Entities/EntityQuery.cs
@@ -39,9 +39,24 @@ public string? InstanceIdStartsWith
         get => this.instanceIdStartsWith;
         init
         {
-            // prefix '@' if filter value provided and not already prefixed with '@'.
-            this.instanceIdStartsWith = value?.Length > 0 && value[0] != '@'
-                ? $"@{value}" : value;
+            if (value != null)
+            {
+                // prefix '@' if filter value provided and not already prefixed with '@'.
+                string prefix = value.Length == 0 || value[0] != '@' ? $"@{value}" : value;
+
+                // check if there is a name-key separator in the string
+                int pos = prefix.IndexOf('@', 1);
+                if (pos != -1)
+                {
+                    // selectively normalize only the part up until that separator
+                    this.instanceIdStartsWith = prefix.Substring(0, pos).ToLowerInvariant() + prefix.Substring(pos);
+                }
+                else
+                {
+                    // normalize the entire prefix
+                    this.instanceIdStartsWith = prefix.ToLowerInvariant();
+                }
+            }
         }
     }
 
diff --git a/src/Client/Grpc/GrpcDurableTaskClient.cs b/src/Client/Grpc/GrpcDurableTaskClient.cs
index a6ad1b12e..b0efbb933 100644
--- a/src/Client/Grpc/GrpcDurableTaskClient.cs
+++ b/src/Client/Grpc/GrpcDurableTaskClient.cs
@@ -20,7 +20,7 @@ public sealed class GrpcDurableTaskClient : DurableTaskClient
     readonly ILogger logger;
     readonly TaskHubSidecarServiceClient sidecarClient;
     readonly GrpcDurableTaskClientOptions options;
-    readonly DurableEntityClient entityClient;
+    readonly DurableEntityClient? entityClient;
     AsyncDisposable asyncDisposable;
 
     /// <summary>
@@ -49,11 +49,16 @@ public GrpcDurableTaskClient(string name, GrpcDurableTaskClientOptions options,
         this.options = Check.NotNull(options);
         this.asyncDisposable = GetCallInvoker(options, out CallInvoker callInvoker);
         this.sidecarClient = new TaskHubSidecarServiceClient(callInvoker);
-        this.entityClient = new GrpcDurableEntityClient(this.Name, this.DataConverter, this.sidecarClient, logger);
+
+        if (this.options.EnableEntitySupport)
+        {
+            this.entityClient = new GrpcDurableEntityClient(this.Name, this.DataConverter, this.sidecarClient, logger);
+        }
     }
 
     /// <inheritdoc/>
-    public override DurableEntityClient Entities => this.entityClient;
+    public override DurableEntityClient Entities => this.entityClient
+        ?? throw new NotSupportedException($"Durable entities are disabled because {nameof(DurableTaskClientOptions)}.{nameof(DurableTaskClientOptions.EnableEntitySupport)}=false");
 
     DataConverter DataConverter => this.options.DataConverter;
 
@@ -70,6 +75,8 @@ public override async Task<string> ScheduleNewOrchestrationInstanceAsync(
         StartOrchestrationOptions? options = null,
         CancellationToken cancellation = default)
     {
+        Check.NotEntity(this.options.EnableEntitySupport, options?.InstanceId);
+
         var request = new P.CreateInstanceRequest
         {
             Name = orchestratorName.Name,
@@ -103,6 +110,8 @@ public override async Task RaiseEventAsync(
         Check.NotNullOrEmpty(instanceId);
         Check.NotNullOrEmpty(eventName);
 
+        Check.NotEntity(this.options.EnableEntitySupport, instanceId);
+
         P.RaiseEventRequest request = new()
         {
             InstanceId = instanceId,
@@ -118,6 +127,8 @@ public override async Task TerminateInstanceAsync(
         string instanceId, object? output = null, CancellationToken cancellation = default)
     {
         Check.NotNullOrEmpty(instanceId);
+        Check.NotEntity(this.options.EnableEntitySupport, instanceId);
+
         this.logger.TerminatingInstance(instanceId);
 
         string? serializedOutput = this.DataConverter.Serialize(output);
@@ -134,6 +145,8 @@ await this.sidecarClient.TerminateInstanceAsync(
     public override async Task SuspendInstanceAsync(
         string instanceId, string? reason = null, CancellationToken cancellation = default)
     {
+        Check.NotEntity(this.options.EnableEntitySupport, instanceId);
+
         P.SuspendRequest request = new()
         {
             InstanceId = instanceId,
@@ -155,6 +168,8 @@ public override async Task SuspendInstanceAsync(
     public override async Task ResumeInstanceAsync(
         string instanceId, string? reason = null, CancellationToken cancellation = default)
     {
+        Check.NotEntity(this.options.EnableEntitySupport, instanceId);
+
         P.ResumeRequest request = new()
         {
             InstanceId = instanceId,
@@ -176,6 +191,8 @@ public override async Task ResumeInstanceAsync(
     public override async Task<OrchestrationMetadata?> GetInstancesAsync(
         string instanceId, bool getInputsAndOutputs = false, CancellationToken cancellation = default)
     {
+        Check.NotEntity(this.options.EnableEntitySupport, instanceId);
+
         if (string.IsNullOrEmpty(instanceId))
         {
             throw new ArgumentNullException(nameof(instanceId));
@@ -201,6 +218,8 @@ public override async Task ResumeInstanceAsync(
     /// <inheritdoc/>
     public override AsyncPageable<OrchestrationMetadata> GetAllInstancesAsync(OrchestrationQuery? filter = null)
     {
+        Check.NotEntity(this.options.EnableEntitySupport, filter?.InstanceIdPrefix);
+
         return Pageable.Create(async (continuation, pageSize, cancellation) =>
         {
             P.QueryInstancesRequest request = new()
@@ -250,6 +269,8 @@ public override AsyncPageable<OrchestrationMetadata> GetAllInstancesAsync(Orches
     public override async Task<OrchestrationMetadata> WaitForInstanceStartAsync(
         string instanceId, bool getInputsAndOutputs = false, CancellationToken cancellation = default)
     {
+        Check.NotEntity(this.options.EnableEntitySupport, instanceId);
+
         this.logger.WaitingForInstanceStart(instanceId, getInputsAndOutputs);
 
         P.GetInstanceRequest request = new()
@@ -275,6 +296,8 @@ public override async Task<OrchestrationMetadata> WaitForInstanceStartAsync(
     public override async Task<OrchestrationMetadata> WaitForInstanceCompletionAsync(
         string instanceId, bool getInputsAndOutputs = false, CancellationToken cancellation = default)
     {
+        Check.NotEntity(this.options.EnableEntitySupport, instanceId);
+
         this.logger.WaitingForInstanceCompletion(instanceId, getInputsAndOutputs);
 
         P.GetInstanceRequest request = new()
diff --git a/src/Shared/Core/Validation/Check.cs b/src/Shared/Core/Validation/Check.cs
index f7acd310f..76c154749 100644
--- a/src/Shared/Core/Validation/Check.cs
+++ b/src/Shared/Core/Validation/Check.cs
@@ -94,6 +94,20 @@ public static string NotNullOrEmpty(
         return argument;
     }
 
+    /// <summary>
+    /// Checks that, if entity support is enabled, the given string is not an entity instance id, and throws an <see cref="ArgumentException"/> otherwise.
+    /// </summary>
+    /// <param name="entitySupportEnabled">Whether entity support is enabled.</param>
+    /// <param name="instanceId">The instance id.</param>
+    /// <param name="argument">The name of the argument.</param>
+    public static void NotEntity(bool entitySupportEnabled, string? instanceId, [CallerArgumentExpression("instanceId")] string? argument = default)
+    {
+        if (entitySupportEnabled && instanceId?.Length > 0 && instanceId[0] == '@')
+        {
+            throw new ArgumentException("Instance IDs starting with '@' are reserved for entities, and must not be used for orchestrations, when entity support is enabled.", argument);
+        }
+    }
+
     /// <summary>
     /// Checks if the supplied type is a concrete non-abstract type and implements the provided generic type.
     /// Throws <see cref="ArgumentException" /> if the conditions are not met.
diff --git a/src/Worker/Core/DurableTaskWorkerOptions.cs b/src/Worker/Core/DurableTaskWorkerOptions.cs
index 4a5b7c98e..bc1e7fc4f 100644
--- a/src/Worker/Core/DurableTaskWorkerOptions.cs
+++ b/src/Worker/Core/DurableTaskWorkerOptions.cs
@@ -44,6 +44,12 @@ public DataConverter DataConverter
         }
     }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether this client should support entities. If true, all instance ids starting with '@' are reserved for entities,
+    /// and validation checks are performed where appropriate.
+    /// </summary>
+    public bool EnableEntitySupport { get; set; }
+
     /// <summary>
     /// Gets or sets the maximum timer interval for the
     /// <see cref="TaskOrchestrationContext.CreateTimer(TimeSpan, CancellationToken)"/> method.
@@ -99,6 +105,7 @@ internal void ApplyTo(DurableTaskWorkerOptions other)
             // Make sure to keep this up to date as values are added.
             other.DataConverter = this.DataConverter;
             other.MaximumTimerInterval = this.MaximumTimerInterval;
+            other.EnableEntitySupport = this.EnableEntitySupport;
         }
     }
 }
diff --git a/src/Worker/Core/Shims/TaskEntityShim.cs b/src/Worker/Core/Shims/TaskEntityShim.cs
index 23d76c1af..3be50b56c 100644
--- a/src/Worker/Core/Shims/TaskEntityShim.cs
+++ b/src/Worker/Core/Shims/TaskEntityShim.cs
@@ -195,8 +195,7 @@ public void Reset()
 
         public override void SignalEntity(EntityInstanceId id, string operationName, object? input = null, SignalEntityOptions? options = null)
         {
-            Check.NotNullOrEmpty(id.Name);
-            Check.NotNull(id.Key);
+            Check.NotDefault(id);
 
             this.operationActions.Add(new SendSignalOperationAction()
             {
@@ -209,6 +208,8 @@ public override void SignalEntity(EntityInstanceId id, string operationName, obj
 
         public override void StartOrchestration(TaskName name, object? input = null, StartOrchestrationOptions? options = null)
         {
+            Check.NotEntity(true, options?.InstanceId);
+
             this.operationActions.Add(new StartNewOrchestrationOperationAction()
             {
                 Name = name.Name,
diff --git a/src/Worker/Core/Shims/TaskOrchestrationContextWrapper.cs b/src/Worker/Core/Shims/TaskOrchestrationContextWrapper.cs
index b9e1484fb..08a7ae824 100644
--- a/src/Worker/Core/Shims/TaskOrchestrationContextWrapper.cs
+++ b/src/Worker/Core/Shims/TaskOrchestrationContextWrapper.cs
@@ -61,7 +61,24 @@ public TaskOrchestrationContextWrapper(
 
     /// <inheritdoc/>
     public override TaskOrchestrationEntityFeature Entities
-        => this.entityFeature ??= new TaskOrchestrationEntityContext(this);
+    {
+        get
+        {
+            if (this.entityFeature == null)
+            {
+                if (this.invocationContext.Options.EnableEntitySupport)
+                {
+                    this.entityFeature = new TaskOrchestrationEntityContext(this);
+                }
+                else
+                {
+                    throw new NotSupportedException($"Durable entities are disabled because {nameof(DurableTaskWorkerOptions)}.{nameof(DurableTaskWorkerOptions.EnableEntitySupport)}=false");
+                }
+            }
+
+            return this.entityFeature;
+        }
+    }
 
     /// <summary>
     /// Gets the DataConverter to use for inputs, outputs, and entity states.
@@ -134,6 +151,8 @@ public override async Task<TResult> CallSubOrchestratorAsync<TResult>(
             => options is SubOrchestrationOptions derived ? derived.InstanceId : null;
         string instanceId = GetInstanceId(options) ?? this.NewGuid().ToString("N");
 
+        Check.NotEntity(this.invocationContext.Options.EnableEntitySupport, instanceId);
+
         // if this orchestration uses entities, first validate that the suborchsestration call is allowed in the current context
         if (this.entityFeature != null && !this.entityFeature.EntityContext.ValidateSuborchestrationTransition(out string? errorMsg))
         {
@@ -233,6 +252,8 @@ public override Task<T> WaitForExternalEvent<T>(string eventName, CancellationTo
     /// <inheritdoc/>
     public override void SendEvent(string instanceId, string eventName, object eventData)
     {
+        Check.NotEntity(this.invocationContext.Options.EnableEntitySupport, instanceId);
+
         this.innerContext.SendEvent(new OrchestrationInstance { InstanceId = instanceId }, eventName, eventData);
     }
 
diff --git a/src/Worker/Core/Shims/TaskOrchestrationEntityContext.cs b/src/Worker/Core/Shims/TaskOrchestrationEntityContext.cs
index 5f47b43ae..514abbe5e 100644
--- a/src/Worker/Core/Shims/TaskOrchestrationEntityContext.cs
+++ b/src/Worker/Core/Shims/TaskOrchestrationEntityContext.cs
@@ -89,9 +89,7 @@ public override async Task<IAsyncDisposable> LockEntitiesAsync(IEnumerable<Entit
         /// <inheritdoc/>
         public override async Task<TResult> CallEntityAsync<TResult>(EntityInstanceId id, string operationName, object? input = null, CallEntityOptions? options = null)
         {
-            Check.NotNullOrEmpty(id.Name);
-            Check.NotNull(id.Key);
-
+            Check.NotDefault(id);
             OperationResult operationResult = await this.CallEntityInternalAsync(id, operationName, input);
 
             if (operationResult.IsError)
@@ -107,9 +105,7 @@ public override async Task<TResult> CallEntityAsync<TResult>(EntityInstanceId id
         /// <inheritdoc/>
         public override async Task CallEntityAsync(EntityInstanceId id, string operationName, object? input = null, CallEntityOptions? options = null)
         {
-            Check.NotNullOrEmpty(id.Name);
-            Check.NotNull(id.Key);
-
+            Check.NotDefault(id);
             OperationResult operationResult = await this.CallEntityInternalAsync(id, operationName, input);
 
             if (operationResult.IsError)
@@ -121,9 +117,7 @@ public override async Task CallEntityAsync(EntityInstanceId id, string operation
         /// <inheritdoc/>
         public override Task SignalEntityAsync(EntityInstanceId id, string operationName, object? input = null, SignalEntityOptions? options = null)
         {
-            Check.NotNullOrEmpty(id.Name);
-            Check.NotNull(id.Key);
-
+            Check.NotDefault(id);
             this.SendOperationMessage(id.ToString(), operationName, input, oneWay: true, scheduledTime: options?.SignalTime);
             return Task.CompletedTask;
         }