diff --git a/hermes_cli/update_cmd.py b/hermes_cli/update_cmd.py
index c99d56a81e18b..148bdba7b4f04 100644
--- a/hermes_cli/update_cmd.py
+++ b/hermes_cli/update_cmd.py
@@ -3744,9 +3744,22 @@ def _cmd_update_impl(args, gateway_mode: bool):
         # against.
         branch = _m()._resolve_update_branch(args)
 
+        # Detect shallow repo — a plain `git fetch` would unshallow it,
+        # dragging in the entire history (the exact cost `--depth 1` avoided).
+        is_shallow = (
+            subprocess.run(
+                git_cmd + ["rev-parse", "--is-shallow-repository"],
+                cwd=_m().PROJECT_ROOT,
+                capture_output=True,
+                text=True, encoding="utf-8", errors="replace",
+            ).stdout.strip()
+            == "true"
+        )
+        depth_args = ["--depth", "1"] if is_shallow else []
+
         print("→ Fetching updates...")
         fetch_result = subprocess.run(
-            git_cmd + ["fetch", "origin", branch],
+            git_cmd + ["fetch"] + depth_args + ["origin", branch],
             cwd=_m().PROJECT_ROOT,
             capture_output=True,
             text=True, encoding="utf-8", errors="replace",