diff --git a/ShoppingAssistantApi.Application/IServices/IOpenAiService.cs b/ShoppingAssistantApi.Application/IServices/IOpenAiService.cs
new file mode 100644
index 0000000..df56a10
--- /dev/null
+++ b/ShoppingAssistantApi.Application/IServices/IOpenAiService.cs
@@ -0,0 +1,13 @@
+using ShoppingAssistantApi.Application.Models.OpenAi;
+
+namespace ShoppingAssistantApi.Application.IServices;
+
+public interface IOpenAiService
+{
+    Task<OpenAiMessage> GetChatCompletion(ChatCompletionRequest chat, CancellationToken cancellationToken);
+
+    /// <summary>
+    /// Retrieves a stream of tokens (pieces of words) based on provided chat.
+    /// </summary>
+    IAsyncEnumerable<string> GetChatCompletionStream(ChatCompletionRequest chat, CancellationToken cancellationToken);
+}
diff --git a/ShoppingAssistantApi.Application/Models/OpenAi/ChatCompletionRequest.cs b/ShoppingAssistantApi.Application/Models/OpenAi/ChatCompletionRequest.cs
new file mode 100644
index 0000000..d2ad66b
--- /dev/null
+++ b/ShoppingAssistantApi.Application/Models/OpenAi/ChatCompletionRequest.cs
@@ -0,0 +1,14 @@
+namespace ShoppingAssistantApi.Application.Models.OpenAi;
+
+public class ChatCompletionRequest
+{
+    public string Model { get; set; } = "gpt-3.5-turbo";
+
+    public List<OpenAiMessage> Messages { get; set; }
+
+    public double Temperature { get; set; } = 0.7;
+
+    public int MaxTokens { get; set; } = 256;
+
+    public bool Stream { get; set; } = false;
+}
diff --git a/ShoppingAssistantApi.Application/Models/OpenAi/OpenAiMessage.cs b/ShoppingAssistantApi.Application/Models/OpenAi/OpenAiMessage.cs
new file mode 100644
index 0000000..91bd757
--- /dev/null
+++ b/ShoppingAssistantApi.Application/Models/OpenAi/OpenAiMessage.cs
@@ -0,0 +1,10 @@
+using ShoppingAssistantApi.Domain.Enums;
+
+namespace ShoppingAssistantApi.Application.Models.OpenAi;
+
+public class OpenAiMessage
+{
+    public OpenAiRole Role { get; set; }
+
+    public string Content { get; set; }
+}
diff --git a/ShoppingAssistantApi.Domain/Enums/OpenAiRole.cs b/ShoppingAssistantApi.Domain/Enums/OpenAiRole.cs
new file mode 100644
index 0000000..54d2c0a
--- /dev/null
+++ b/ShoppingAssistantApi.Domain/Enums/OpenAiRole.cs
@@ -0,0 +1,8 @@
+namespace ShoppingAssistantApi.Domain.Enums;
+
+public enum OpenAiRole
+{
+    System,
+    User,
+    Assistant
+}
diff --git a/ShoppingAssistantApi.Infrastructure/Services/OpenAiService.cs b/ShoppingAssistantApi.Infrastructure/Services/OpenAiService.cs
index 097100e..9ed750a 100644
--- a/ShoppingAssistantApi.Infrastructure/Services/OpenAiService.cs
+++ b/ShoppingAssistantApi.Infrastructure/Services/OpenAiService.cs
@@ -1,11 +1,24 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Threading.Tasks;
+using ShoppingAssistantApi.Application.IServices;
+using ShoppingAssistantApi.Application.Models.OpenAi;
 
 namespace ShoppingAssistantApi.Infrastructure.Services;
 
-public class OpenAiService
+public class OpenAiService : IOpenAiService
 {
-    
+    private readonly HttpClient _httpClient;
+
+    public OpenAiService(HttpClient client)
+    {
+        _httpClient = client;
+    }
+
+    public Task<OpenAiMessage> GetChatCompletion(ChatCompletionRequest chat, CancellationToken cancellationToken)
+    {
+        throw new NotImplementedException();
+    }
+
+    public IAsyncEnumerable<string> GetChatCompletionStream(ChatCompletionRequest chat, CancellationToken cancellationToken)
+    {
+        throw new NotImplementedException();
+    }
 }