diff --git a/SVSim.EmulatedEntrypoint/Models/Dtos/Requests/ImmutableData/CardMasterRequest.cs b/SVSim.EmulatedEntrypoint/Models/Dtos/Requests/ImmutableData/CardMasterRequest.cs
new file mode 100644
index 00000000..e9584d26
--- /dev/null
+++ b/SVSim.EmulatedEntrypoint/Models/Dtos/Requests/ImmutableData/CardMasterRequest.cs
@@ -0,0 +1,18 @@
+using MessagePack;
+using System.Text.Json.Serialization;
+using SVSim.EmulatedEntrypoint.Models.Dtos.Requests;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Requests.ImmutableData;
+
+/// <summary>
+/// Wire body for <c>POST /immutable_data/card_master</c>. Client populates from
+/// <c>GetCardMasterTask.CardMasterTaskParam</c> (Wizard/GetCardMasterTask.cs:14). For Tier 1
+/// the hash is bound only for completeness — the controller serves the static blob regardless.
+/// </summary>
+[MessagePackObject]
+public class CardMasterRequest : BaseRequest
+{
+    [JsonPropertyName("card_master_hash")]
+    [Key("card_master_hash")]
+    public string? CardMasterHash { get; set; }
+}
diff --git a/SVSim.EmulatedEntrypoint/Models/Dtos/Responses/ImmutableData/CardMasterResponse.cs b/SVSim.EmulatedEntrypoint/Models/Dtos/Responses/ImmutableData/CardMasterResponse.cs
new file mode 100644
index 00000000..c23b2a2b
--- /dev/null
+++ b/SVSim.EmulatedEntrypoint/Models/Dtos/Responses/ImmutableData/CardMasterResponse.cs
@@ -0,0 +1,17 @@
+using MessagePack;
+using System.Text.Json.Serialization;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Responses.ImmutableData;
+
+/// <summary>
+/// Wire response shape. Client decodes <c>card_master</c> via:
+/// <c>Convert.FromBase64String</c> → <c>GZipStream.UncompressBuffer</c> → UTF-8 decode →
+/// <c>JsonMapper.ToObject</c>, yielding a dict <c>{ "1": "&lt;csv&gt;", "2"?: "&lt;csv&gt;" }</c>.
+/// </summary>
+[MessagePackObject]
+public class CardMasterResponse
+{
+    [JsonPropertyName("card_master")]
+    [Key("card_master")]
+    public string CardMaster { get; set; } = "";
+}