diff --git a/metropolis/installer/test/testos/BUILD.bazel b/metropolis/installer/test/testos/BUILD.bazel
index e8d8700..34f346b 100644
--- a/metropolis/installer/test/testos/BUILD.bazel
+++ b/metropolis/installer/test/testos/BUILD.bazel
@@ -1,5 +1,4 @@
 load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
-load("@rules_pkg//:pkg.bzl", "pkg_zip")
 load("//osbase/build/mkerofs:def.bzl", "erofs_image")
 load("//osbase/build/mkoci:def.bzl", "oci_os_image")
 load("//osbase/build/mkpayload:def.bzl", "efi_unified_kernel_image")
@@ -24,18 +23,6 @@
     verity = ":verity_rootfs",
 )
 
-# An intermediary "bundle" format until we finalize the actual bundle format. This is NOT stable until migrated
-# to the actual bundle format.
-# TODO(lorenz): Replace this
-pkg_zip(
-    name = "testos_bundle",
-    srcs = [
-        ":kernel_efi",
-        ":verity_rootfs",
-    ],
-    visibility = ["//visibility:public"],
-)
-
 oci_os_image(
     name = "testos_image",
     srcs = {
diff --git a/metropolis/proto/api/management.proto b/metropolis/proto/api/management.proto
index 9a81082..81d4ca0 100644
--- a/metropolis/proto/api/management.proto
+++ b/metropolis/proto/api/management.proto
@@ -481,6 +481,21 @@
   ActivationMode activation_mode = 3;
 }
 
+// OSImageRef contains the parameters for fetching an OS image from an OCI
+// registry.
+message OSImageRef {
+  // Scheme must be either http or https.
+  string scheme = 1;
+  // Host with optional port.
+  string host = 2;
+  // Repository containing the image.
+  string repository = 3;
+  // Tag is optional. If not set, the manifest is fetched by digest instead.
+  string tag = 4;
+  // Digest is required. It is used to verify the manifest.
+  string digest = 5;
+}
+
 message UpdateNodeResponse {}
 
 message UpdateNodeLabelsRequest {
@@ -538,4 +553,4 @@
 message ConfigureClusterResponse {
     // Resulting config as set on the server, merged from the users new_config.
     common.ClusterConfiguration resulting_config = 1;
-}
\ No newline at end of file
+}