diff --git a/tests/test_model_prices_unique_keys.py b/tests/test_model_prices_unique_keys.py
new file mode 100644
index 00000000000..876b54576f2
--- /dev/null
+++ b/tests/test_model_prices_unique_keys.py
@@ -0,0 +1,56 @@
+"""The root model cost map must stay a unique-key mirror of the backup, with no negative token costs."""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[1]
+COST_MAP = ROOT / "model_prices_and_context_window.json"
+BACKUP = ROOT / "litellm" / "model_prices_and_context_window_backup.json"
+
+
+def _load_with_duplicate_hook(path: Path) -> tuple[dict, list[str]]:
+    duplicates: list[str] = []
+
+    def hook(pairs: list[tuple[str, object]]) -> dict:
+        seen: dict[str, object] = {}
+        for key, value in pairs:
+            if key in seen:
+                duplicates.append(key)
+            seen[key] = value
+        return seen
+
+    with path.open(encoding="utf-8") as handle:
+        data = json.load(handle, object_pairs_hook=hook)
+    if not isinstance(data, dict):
+        raise TypeError(f"{path} must be a JSON object")
+    return data, duplicates
+
+
+def test_model_prices_unique_keys_and_backup_sync() -> None:
+    root, root_duplicates = _load_with_duplicate_hook(COST_MAP)
+    backup, backup_duplicates = _load_with_duplicate_hook(BACKUP)
+
+    duplicate_key_count = len(root_duplicates) + len(backup_duplicates)
+    assert duplicate_key_count == 0
+    assert root_duplicates == []
+    assert backup_duplicates == []
+
+    only_root = set(root) - set(backup)
+    only_backup = set(backup) - set(root)
+    value_diffs = [key for key in set(root) & set(backup) if root[key] != backup[key]]
+    diff_count = len(only_root) + len(only_backup) + len(value_diffs)
+    assert diff_count == 0
+
+    negative: list[tuple[str, str, int | float]] = []
+    for key, entry in root.items():
+        if not isinstance(entry, dict):
+            continue
+        for field in ("input_cost_per_token", "output_cost_per_token"):
+            cost = entry.get(field)
+            if isinstance(cost, bool) or not isinstance(cost, (int, float)):
+                continue
+            if cost < 0:
+                negative.append((key, field, cost))
+    assert len(negative) == 0