diff --git a/src/dotnet/Common/Constants/Orchestration/MessageContentItemTypes.cs b/src/dotnet/Common/Constants/Orchestration/MessageContentItemTypes.cs
new file mode 100644
index 0000000000..4317366b6f
--- /dev/null
+++ b/src/dotnet/Common/Constants/Orchestration/MessageContentItemTypes.cs
@@ -0,0 +1,23 @@
+namespace FoundationaLLM.Common.Constants.Orchestration
+{
+    /// <summary>
+    /// Contains constants for the types of message content items.
+    /// </summary>
+    public static class MessageContentItemTypes
+    {
+        /// <summary>
+        /// Text content.
+        /// </summary>
+        public const string Text = "text";
+
+        /// <summary>
+        /// Image file content.
+        /// </summary>
+        public const string ImageFile = "image_file";
+
+        /// <summary>
+        /// File path content.
+        /// </summary>
+        public const string FilePath = "file_path";
+    }
+}
diff --git a/src/dotnet/Common/Models/Chat/Message.cs b/src/dotnet/Common/Models/Chat/Message.cs
index a7e730d651..ae7cf53fb5 100644
--- a/src/dotnet/Common/Models/Chat/Message.cs
+++ b/src/dotnet/Common/Models/Chat/Message.cs
@@ -1,5 +1,6 @@
 using Azure.Search.Documents.Indexes;
 using FoundationaLLM.Common.Models.Orchestration;
+using System.Text.Json.Serialization;
 
 namespace FoundationaLLM.Common.Models.Chat;
 
@@ -82,12 +83,18 @@ public record Message
     /// </summary>
     public Citation[]? Citations { get; set; }
 
+    /// <summary>
+    /// The content of the message.
+    /// </summary>
+    [JsonPropertyName("content")]
+    public List<MessageContent>? Content { get; set; }
+
     /// <summary>
     /// Constructor for Message.
     /// </summary>
     public Message(string sessionId, string sender, int? tokens, string text,
         float[]? vector, bool? rating, string upn, string? senderDisplayName = null,
-        Citation[]? citations = null, string? expectedCompletion = null)
+        Citation[]? citations = null, string? expectedCompletion = null, List<MessageContent>? content = null)
     {
         Id = Guid.NewGuid().ToString();
         Type = nameof(Message);
@@ -102,5 +109,6 @@ public Message(string sessionId, string sender, int? tokens, string text,
         UPN = upn;
         ExpectedCompletion = expectedCompletion;
         Citations = citations;
+        Content = content;
     }
 }
diff --git a/src/dotnet/Common/Models/Chat/MessageContent.cs b/src/dotnet/Common/Models/Chat/MessageContent.cs
new file mode 100644
index 0000000000..81d646862a
--- /dev/null
+++ b/src/dotnet/Common/Models/Chat/MessageContent.cs
@@ -0,0 +1,22 @@
+using System.Text.Json.Serialization;
+
+namespace FoundationaLLM.Common.Models.Chat
+{
+    /// <summary>
+    /// Contains parts that compose the message content.
+    /// </summary>
+    public class MessageContent
+    {
+        /// <summary>
+        /// The type of the message content. Could be text, image, etc.
+        /// </summary>
+        [JsonPropertyName("type")]
+        public string? Type { get; set; }
+
+        /// <summary>
+        /// The value of the message content.
+        /// </summary>
+        [JsonPropertyName("value")]
+        public string? Value { get; set; }
+    }
+}
diff --git a/src/dotnet/Common/Models/Orchestration/CompletionResponseBase.cs b/src/dotnet/Common/Models/Orchestration/CompletionResponseBase.cs
index 7c4008099b..27196d6d50 100644
--- a/src/dotnet/Common/Models/Orchestration/CompletionResponseBase.cs
+++ b/src/dotnet/Common/Models/Orchestration/CompletionResponseBase.cs
@@ -19,6 +19,12 @@ public class CompletionResponseBase
         [JsonPropertyName("completion")]
         public string Completion { get; set; }
 
+        /// <summary>
+        /// Content returned from the Assistants API.
+        /// </summary>
+        [JsonPropertyName("content")]
+        public List<MessageContentItemBase>? Content { get; set; }
+
         /// <summary>
         /// The citations used in building the completion response.
         /// </summary>
diff --git a/src/dotnet/Common/Models/Orchestration/MessageContentItemBase.cs b/src/dotnet/Common/Models/Orchestration/MessageContentItemBase.cs
new file mode 100644
index 0000000000..2800b645a7
--- /dev/null
+++ b/src/dotnet/Common/Models/Orchestration/MessageContentItemBase.cs
@@ -0,0 +1,22 @@
+using FoundationaLLM.Common.Constants.Orchestration;
+using System.Text.Json.Serialization;
+
+namespace FoundationaLLM.Common.Models.Orchestration
+{
+    /// <summary>
+    /// Base message content item model.
+    /// </summary>
+    [JsonPolymorphic(TypeDiscriminatorPropertyName = "type")]
+    [JsonDerivedType(typeof(OpenAITextMessageContentItem), MessageContentItemTypes.Text)]
+    [JsonDerivedType(typeof(OpenAIImageFileMessageContentItem), MessageContentItemTypes.ImageFile)]
+    [JsonDerivedType(typeof(OpenAIFilePathContentItem), MessageContentItemTypes.FilePath)]
+    public class MessageContentItemBase
+    {
+        /// <summary>
+        /// The type of the message content item.
+        /// </summary>
+        [JsonPropertyName("type")]
+        [JsonPropertyOrder(-100)]
+        public virtual string? Type { get; set; }
+    }
+}
diff --git a/src/dotnet/Common/Models/Orchestration/OpenAIFilePathContentItem.cs b/src/dotnet/Common/Models/Orchestration/OpenAIFilePathContentItem.cs
new file mode 100644
index 0000000000..f23cb71090
--- /dev/null
+++ b/src/dotnet/Common/Models/Orchestration/OpenAIFilePathContentItem.cs
@@ -0,0 +1,45 @@
+using FoundationaLLM.Common.Constants.Orchestration;
+using System.Text.Json.Serialization;
+
+namespace FoundationaLLM.Common.Models.Orchestration
+{
+    /// <summary>
+    /// File content item used to generate a message content item.
+    /// </summary>
+    public class OpenAIFilePathContentItem : MessageContentItemBase
+    {
+        /// <inheritdoc/>
+        [JsonIgnore]
+        public override string? Type { get; set; }
+
+        /// <summary>
+        /// The text of the annotation.
+        /// </summary>
+        [JsonPropertyName("text")]
+        public string? Text { get; set; }
+
+        /// <summary>
+        /// The starting index of the annotation.
+        /// </summary>
+        [JsonPropertyName("start_index")]
+        public int? StartIndex { get; set; }
+
+        /// <summary>
+        /// The ending index of the annotation.
+        /// </summary>
+        [JsonPropertyName("end_index")]
+        public int? EndIndex { get; set; }
+
+        /// <summary>
+        /// The ID of the file referenced by the annotation.
+        /// </summary>
+        [JsonPropertyName("file_id")]
+        public string? FileId { get; set; }
+
+        /// <summary>
+        /// Set default property values.
+        /// </summary>
+        public OpenAIFilePathContentItem() =>
+            Type = MessageContentItemTypes.FilePath;
+    }
+}
diff --git a/src/dotnet/Common/Models/Orchestration/OpenAIImageFileMessageContentItem.cs b/src/dotnet/Common/Models/Orchestration/OpenAIImageFileMessageContentItem.cs
new file mode 100644
index 0000000000..d322eac2b8
--- /dev/null
+++ b/src/dotnet/Common/Models/Orchestration/OpenAIImageFileMessageContentItem.cs
@@ -0,0 +1,33 @@
+using FoundationaLLM.Common.Constants.Orchestration;
+using System.Text.Json.Serialization;
+
+namespace FoundationaLLM.Common.Models.Orchestration
+{
+    /// <summary>
+    /// An OpenAI image file message content item.
+    /// </summary>
+    public class OpenAIImageFileMessageContentItem : MessageContentItemBase
+    {
+        /// <inheritdoc/>
+        [JsonIgnore]
+        public override string? Type { get; set; }
+
+        /// <summary>
+        /// The ID of the image file.
+        /// </summary>
+        [JsonPropertyName("file_id")]
+        public string? FileId { get; set; }
+
+        /// <summary>
+        /// The URL of the image file.
+        /// </summary>
+        [JsonPropertyName("file_url")]
+        public string? FileUrl { get; set; }
+
+        /// <summary>
+        /// Set default property values.
+        /// </summary>
+        public OpenAIImageFileMessageContentItem() =>
+            Type = MessageContentItemTypes.ImageFile;
+    }
+}
diff --git a/src/dotnet/Common/Models/Orchestration/OpenAITextMessageContentItem.cs b/src/dotnet/Common/Models/Orchestration/OpenAITextMessageContentItem.cs
new file mode 100644
index 0000000000..cd9cbdd023
--- /dev/null
+++ b/src/dotnet/Common/Models/Orchestration/OpenAITextMessageContentItem.cs
@@ -0,0 +1,33 @@
+using FoundationaLLM.Common.Constants.Orchestration;
+using System.Text.Json.Serialization;
+
+namespace FoundationaLLM.Common.Models.Orchestration
+{
+    /// <summary>
+    /// An OpenAI text message content item.
+    /// </summary>
+    public class OpenAITextMessageContentItem : MessageContentItemBase
+    {
+        /// <inheritdoc/>
+        [JsonIgnore]
+        public override string? Type { get; set; }
+
+        /// <summary>
+        /// A list of file annotations used to generate the message content item.
+        /// </summary>
+        [JsonPropertyName("annotations")]
+        public List<OpenAIFilePathContentItem> Annotations { get; set; } = [];
+
+        /// <summary>
+        /// The text value of the message content item.
+        /// </summary>
+        [JsonPropertyName("value")]
+        public string? Value { get; set; }
+
+        /// <summary>
+        /// Set default property values.
+        /// </summary>
+        public OpenAITextMessageContentItem() =>
+            Type = MessageContentItemTypes.Text;
+    }
+}