diff --git a/infrastructure/s3/s3_client.py b/infrastructure/s3/s3_client.py
index eb2a68f5c..7e26c790b 100644
--- a/infrastructure/s3/s3_client.py
+++ b/infrastructure/s3/s3_client.py
@@ -21,6 +21,12 @@ class S3Client:
         self._client.put_object(Bucket=self._bucket, Key=key, Body=body)
         return f"s3://{self._bucket}/{key}"
 
+    def upload_file(self, local_path: str, key: str) -> str:
+        """Upload a file from local disk, using boto's managed transfer so a
+        large object (a multi-GB Download Package ZIP, ADR-0060) is streamed in
+        multipart from ``/tmp`` rather than held in memory."""
+        raise NotImplementedError
+
     def generate_presigned_url(self, key: str, expires_in: int) -> str:
         """A time-limited URL that lets the holder GET this object without AWS
         credentials (ADR-0060 — how a Download Package link is delivered).
diff --git a/tests/infrastructure/test_s3_client.py b/tests/infrastructure/test_s3_client.py
index b867dd26c..13e6c4714 100644
--- a/tests/infrastructure/test_s3_client.py
+++ b/tests/infrastructure/test_s3_client.py
@@ -47,3 +47,20 @@ def test_generate_presigned_url_signs_a_get_for_the_object(s3_client: S3Client)
     assert BUCKET in url
     assert "bulk-downloads/pkg.zip" in url
     assert "Signature" in url
+
+
+def test_upload_file_streams_a_local_file_to_s3(
+    s3_client: S3Client, tmp_path: object
+) -> None:
+    # arrange — a file on local disk (stands in for the /tmp ZIP)
+    from pathlib import Path
+
+    local = Path(str(tmp_path)) / "package.zip"
+    local.write_bytes(b"ZIP-CONTENT")
+
+    # act
+    uri = s3_client.upload_file(str(local), "bulk-downloads/package.zip")
+
+    # assert — the object landed with the file's bytes
+    assert uri == f"s3://{BUCKET}/bulk-downloads/package.zip"
+    assert s3_client.get_object("bulk-downloads/package.zip") == b"ZIP-CONTENT"