diff --git a/orchestration/bulk_document_download_orchestrator.py b/orchestration/bulk_document_download_orchestrator.py
index 39ee7271e..ba979a1c6 100644
--- a/orchestration/bulk_document_download_orchestrator.py
+++ b/orchestration/bulk_document_download_orchestrator.py
@@ -10,7 +10,8 @@ rows are reported, not fatal; a wholly-empty selection is a recorded failure
 
 from __future__ import annotations
 
-import io
+import os
+import tempfile
 import zipfile
 from dataclasses import dataclass
 from datetime import datetime
@@ -99,15 +100,20 @@ class BulkDocumentDownloadOrchestrator:
                 },
             )
 
-        buffer = io.BytesIO()
-        with zipfile.ZipFile(buffer, "w", zipfile.ZIP_DEFLATED) as archive:
-            for entry in plan.entries:
-                archive.writestr(
-                    entry.zip_path, self._documents.read(entry.s3_bucket, entry.s3_key)
-                )
-
+        # Stream to a /tmp file and multipart-upload it (ADR-0060): a Download
+        # Package can be several GB, so it is never held whole in memory — each
+        # source file is read, written into the on-disk ZIP, and released; the
+        # finished archive is streamed up from disk.
         key = f"{self._package_key_prefix}/{package_name}.zip"
-        self._packages.put_object(key, buffer.getvalue())
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            zip_path = os.path.join(tmp_dir, "package.zip")
+            with zipfile.ZipFile(zip_path, "w", zipfile.ZIP_DEFLATED) as archive:
+                for entry in plan.entries:
+                    archive.writestr(
+                        entry.zip_path,
+                        self._documents.read(entry.s3_bucket, entry.s3_key),
+                    )
+            self._packages.upload_file(zip_path, key)
         url = self._packages.generate_presigned_url(key, self._url_ttl_seconds)
 
         self._email.send(