diff --git a/SVSim.EmulatedEntrypoint/Controllers/AccountController.cs b/SVSim.EmulatedEntrypoint/Controllers/AccountController.cs
index bc9be0cd..91a41b12 100644
--- a/SVSim.EmulatedEntrypoint/Controllers/AccountController.cs
+++ b/SVSim.EmulatedEntrypoint/Controllers/AccountController.cs
@@ -1,6 +1,7 @@
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.EntityFrameworkCore;
 using SVSim.Database;
+using SVSim.EmulatedEntrypoint.Models.Dtos.Common;
 using SVSim.EmulatedEntrypoint.Models.Dtos.Requests.Account;
 
 namespace SVSim.EmulatedEntrypoint.Controllers;
@@ -46,4 +47,14 @@ public class AccountController : SVSimController
         // so the translation middleware emits the right msgpack shape.
         return Ok(Array.Empty<object>());
     }
+
+    [HttpPost("update_region_code")]
+    public ActionResult<EmptyResponse> UpdateRegionCode([FromBody] AccountUpdateRegionCodeRequest _)
+    {
+        if (!TryGetViewerId(out long __)) return Unauthorized();
+        // No-op: actual region value is sent in the REGION_CODE HTTP header, which we
+        // don't currently consume server-side. The body carries only initialize_flag,
+        // which is a first-set-vs-update signal we have no use for yet.
+        return new EmptyResponse();
+    }
 }
diff --git a/SVSim.EmulatedEntrypoint/Models/Dtos/Requests/Account/AccountUpdateRegionCodeRequest.cs b/SVSim.EmulatedEntrypoint/Models/Dtos/Requests/Account/AccountUpdateRegionCodeRequest.cs
new file mode 100644
index 00000000..ed640c0f
--- /dev/null
+++ b/SVSim.EmulatedEntrypoint/Models/Dtos/Requests/Account/AccountUpdateRegionCodeRequest.cs
@@ -0,0 +1,12 @@
+using MessagePack;
+using System.Text.Json.Serialization;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Requests.Account;
+
+[MessagePackObject]
+public class AccountUpdateRegionCodeRequest : BaseRequest
+{
+    [JsonPropertyName("initialize_flag")]
+    [Key("initialize_flag")]
+    public int InitializeFlag { get; set; }
+}
diff --git a/SVSim.UnitTests/Controllers/AccountControllerUpdateRegionCodeTests.cs b/SVSim.UnitTests/Controllers/AccountControllerUpdateRegionCodeTests.cs
new file mode 100644
index 00000000..dc184717
--- /dev/null
+++ b/SVSim.UnitTests/Controllers/AccountControllerUpdateRegionCodeTests.cs
@@ -0,0 +1,24 @@
+using System.Net;
+using System.Text;
+using NUnit.Framework;
+using SVSim.UnitTests.Infrastructure;
+
+namespace SVSim.UnitTests.Controllers;
+
+public class AccountControllerUpdateRegionCodeTests
+{
+    [TestCase(0)]
+    [TestCase(1)]
+    public async Task UpdateRegionCode_accepts(int initializeFlag)
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync(tutorialState: 0);
+        using var client = factory.CreateAuthenticatedClient(viewerId);
+
+        var requestJson = $$"""{"initialize_flag":{{initializeFlag}},"viewer_id":"0","steam_id":0,"steam_session_ticket":""}""";
+        var response = await client.PostAsync("/account/update_region_code",
+            new StringContent(requestJson, Encoding.UTF8, "application/json"));
+
+        Assert.That(response.StatusCode, Is.EqualTo(HttpStatusCode.OK));
+    }
+}