diff --git a/docs/explanation/protobuf-extension-naming.md b/docs/explanation/protobuf-extension-naming.md
index c76b55b..5f80a33 100644
--- a/docs/explanation/protobuf-extension-naming.md
+++ b/docs/explanation/protobuf-extension-naming.md
@@ -86,7 +86,8 @@ Claim your extension numbers here to prevent conflicts:
 | 870001 | trogon.uuid.v1 | google.protobuf.EnumOptions |
 | 870002 | trogon.uuid.v1 | google.protobuf.EnumValueOptions |
 | 870010 | trogon.object_id.v1alpha1 | google.protobuf.EnumValueOptions |
-| 870011–870999 | *Available* | — |
+| 870011 | trogon.stream.v1alpha1 | google.protobuf.EnumValueOptions |
+| 870012–870999 | *Available* | — |
 
 ## Examples in This Repo
 
@@ -99,6 +100,9 @@ trogon/uuid/v1/options.proto
 
 trogon/object_id/v1alpha1/options.proto
 └─ EnumValueOptions      { object_type, separator } → enum_value (870010)
+
+trogon/stream/v1alpha1/options.proto
+└─ EnumValueOptions      { prefix, separator }      → enum_value (870011)
 ```
 
 ## Field Number Ranges
diff --git a/proto/trogon/stream/v1alpha1/options.proto b/proto/trogon/stream/v1alpha1/options.proto
new file mode 100644
index 0000000..7791ff8
--- /dev/null
+++ b/proto/trogon/stream/v1alpha1/options.proto
@@ -0,0 +1,39 @@
+syntax = "proto3";
+package trogon.stream.v1alpha1;
+
+import "elixirpb.proto";
+import "google/protobuf/descriptor.proto";
+
+option (elixirpb.file).module_prefix = "TrogonProto.Stream.V1Alpha1";
+
+// EnumValueOptions defines enum-value-level options for stream identity prefixes.
+message EnumValueOptions {
+  // The stream prefix for this aggregate (e.g., "order", "account", "fanid").
+  string prefix = 1;
+
+  // Separator between prefix and identity value. Defaults to ":" if not set.
+  optional string separator = 2;
+}
+
+extend google.protobuf.EnumValueOptions {
+  // enum_value specifies the stream identity prefix for an enum value.
+  //
+  // Example usage:
+  //
+  //   // acme/type/v1/stream_prefix.proto
+  //   syntax = "proto3";
+  //   package acme.type.v1;
+  //
+  //   import "trogon/stream/v1alpha1/options.proto";
+  //
+  //   enum StreamPrefix {
+  //     STREAM_PREFIX_UNSPECIFIED = 0;
+  //     STREAM_PREFIX_ORDER = 1 [(trogon.stream.v1alpha1.enum_value).prefix = "order"];
+  //     STREAM_PREFIX_ACCOUNT = 2 [(trogon.stream.v1alpha1.enum_value) = {
+  //       prefix: "account",
+  //       separator: "-"
+  //     }];
+  //   }
+  //
+  optional EnumValueOptions enum_value = 870011;
+}