diff --git a/netbox_inventory.py b/netbox_inventory.py
index 0bea7b5..bcf8da5 100755
--- a/netbox_inventory.py
+++ b/netbox_inventory.py
@@ -66,6 +66,18 @@ def _extract_error_message(response: requests.Response) -> str:
     return f"NetBox API error: HTTP {response.status_code}"
 
 
+def auth_header(token: str) -> str:
+    """
+    Build the Authorization header value for a NetBox API token.
+
+    Version 2 tokens (NetBox 4.5+, "nbt_<key>.<secret>") use the Bearer
+    scheme, legacy tokens the Token scheme.
+    """
+    if token.startswith("nbt_"):
+        return f"Bearer {token}"
+    return f"Token {token}"
+
+
 class NetBoxClient:
     """Thin wrapper around the NetBox REST API."""
 
@@ -76,7 +88,7 @@ class NetBoxClient:
         self._session.verify = verify_ssl
         self._session.headers.update(
             {
-                "Authorization": f"Token {token}",
+                "Authorization": auth_header(token),
                 "Accept": "application/json",
             }
         )
diff --git a/tests/test_inventory.py b/tests/test_inventory.py
index e28cbd8..f3a9837 100644
--- a/tests/test_inventory.py
+++ b/tests/test_inventory.py
@@ -16,6 +16,14 @@ def make_client() -> inv.NetBoxClient:
     return inv.NetBoxClient(NETBOX_URL, "token", verify_ssl=True, timeout=5)
 
 
+class TestAuthHeader:
+    def test_legacy_token_uses_token_scheme(self):
+        assert inv.auth_header("0123456789abcdef") == "Token 0123456789abcdef"
+
+    def test_v2_token_uses_bearer_scheme(self):
+        assert inv.auth_header("nbt_abc.def") == "Bearer nbt_abc.def"
+
+
 class TestStripPrefix:
     def test_strips_prefix_length(self):
         assert inv.strip_prefix("192.0.2.10/24") == "192.0.2.10"