diff --git a/lua/copy_build.lua b/lua/copy_build.lua
index 70af142..43825f1 100644
--- a/lua/copy_build.lua
+++ b/lua/copy_build.lua
@@ -65,29 +65,40 @@ else
   return
 end
 
-local total_number_of_objects = 0
+local objects = {}
 for object in res.body:gmatch("([^\r\n]+)[\r\n]+") do
-  total_number_of_objects = total_number_of_objects + 1
+  table.insert(objects, object)
 end
+
+local total_number_of_objects = #objects
+local batch_size = 16
 local current_object = 0
-for object in res.body:gmatch("([^\r\n]+)[\r\n]+") do
-  local object_url, object_res
 
-  current_object = current_object + 1
-  ngx.say("[" .. current_object .. "/" .. total_number_of_objects .. "] Copying " .. object .. " ... ")
-  ngx.flush(true)
+for batch_start = 1, total_number_of_objects, batch_size do
+  local batch_end = math.min(batch_start + batch_size - 1, total_number_of_objects)
+  local urls = {}
+  for i = batch_start, batch_end do
+    table.insert(urls, {
+      "/force_real_request/copy/" .. build_src .. "/" .. build_tgt .. "/" .. objects[i],
+      { method = ngx.HTTP_PUT, body = '' }
+    })
+  end
 
-  object_url = "/force_real_request/copy/" .. build_src .. "/" .. build_tgt .. "/" .. object
-  object_res = ngx.location.capture(object_url, { method = ngx.HTTP_PUT, body = '' })
+  local results = { ngx.location.capture_multi(urls) }
 
-  if object_res.status == 200 then
-    ngx.say('DONE')
-    ngx.flush(true)
-  else
-    ngx.say('FAILED')
-    ngx.flush(true)
-    return
+  for i, object_res in ipairs(results) do
+    current_object = current_object + 1
+    local object = objects[batch_start + i - 1]
+    ngx.say("[" .. current_object .. "/" .. total_number_of_objects .. "] " .. object .. " ... ")
+    if object_res.status == 200 then
+      ngx.say('DONE')
+    else
+      ngx.say('FAILED')
+      ngx.flush(true)
+      return
+    end
   end
+  ngx.flush(true)
 end
 
 ngx.say("BUILD COPIED")
diff --git a/tests/end2end/test_copy.py b/tests/end2end/test_copy.py
index 0284780..03149bb 100644
--- a/tests/end2end/test_copy.py
+++ b/tests/end2end/test_copy.py
@@ -2,7 +2,7 @@
 
 import pytest
 
-from constants import STAGING_BUILD
+from constants import STAGING_BUILD, PROMOTED_BUILD
 
 
 COPY_BUILD = f'copy_of_{STAGING_BUILD}'
@@ -71,6 +71,34 @@ def test_copy_fails_when_target_already_exists(
     assert lines[-1] == b'FAILED'
 
 
+def test_copy_promotes_staging_to_promoted_bucket(
+    session, artifacts_url, upload_file, finish_build
+):
+    """Copy from a staging build to a promoted build (cross-bucket promotion).
+
+    Uses 19 objects to exercise the multi-batch loop (batch_size=16), and
+    embeds the index in each object's content to catch cross-object regressions.
+    """
+    n = 19
+    for i in range(n):
+        upload_file(STAGING_BUILD, f'obj-{i}', f'content-{i}'.encode())
+    finish_build(STAGING_BUILD)
+
+    resp = session.get(f'{artifacts_url}/copy/{STAGING_BUILD}/{PROMOTED_BUILD}/')
+    assert resp.status_code == 200
+    assert resp.content.splitlines()[-1] == b'BUILD COPIED'
+
+    # Verify every promoted object has the correct content.
+    for i in range(n):
+        dl = session.get(f'{artifacts_url}/download/{PROMOTED_BUILD}/obj-{i}')
+        assert dl.status_code == 200, f'obj-{i} not found in promoted build'
+        assert dl.content == f'content-{i}'.encode(), f'obj-{i} has unexpected content'
+
+    # Verify promotion metadata files are present.
+    assert session.get(f'{artifacts_url}/download/{PROMOTED_BUILD}/.final_status').status_code == 200
+    assert session.get(f'{artifacts_url}/download/{PROMOTED_BUILD}/.original_build').status_code == 200
+
+
 def test_copy_behind_ingress(session, artifacts_url, upload_file, finish_build):
     """Copy works correctly when a Script-Name ingress header is present."""
     upload_file(STAGING_BUILD, '.final_status', b'SUCCESSFUL',)