diff --git a/stripe/_encode.py b/stripe/_encode.py
index 228edfdc6..018417e02 100644
--- a/stripe/_encode.py
+++ b/stripe/_encode.py
@@ -1,6 +1,7 @@
 import calendar
 import datetime
 import time
+import warnings
 from collections import OrderedDict
 from typing import Generator, Tuple, Any
 
@@ -31,25 +32,31 @@ def _api_encode(data) -> Generator[Tuple[str, Any], None, None]:
     for key, value in data.items():
         if value is None:
             continue
-        elif hasattr(value, "stripe_id"):
-            yield (key, value.stripe_id)
-        elif isinstance(value, list) or isinstance(value, tuple):
-            for i, sv in enumerate(value):
-                # Always use indexed format for arrays
-                encoded_key = "%s[%d]" % (key, i)
-                if isinstance(sv, dict):
-                    subdict = _encode_nested_dict(encoded_key, sv)
-                    for k, v in _api_encode(subdict):
-                        yield (k, v)
-                else:
-                    yield (encoded_key, sv)
-        elif isinstance(value, dict):
-            subdict = _encode_nested_dict(key, value)
-            for subkey, subvalue in _api_encode(subdict):
-                yield (subkey, subvalue)
-        elif isinstance(value, datetime.datetime):
-            yield (key, _encode_datetime(value))
-        elif isinstance(value, bool):
-            yield (key, str(value).lower())
         else:
-            yield (key, value)
+            # Check for stripe_id attribute without triggering deprecation warning
+            with warnings.catch_warnings():
+                warnings.simplefilter("ignore", DeprecationWarning)
+                has_stripe_id = hasattr(value, "stripe_id")
+
+            if has_stripe_id and hasattr(value, "id") and getattr(value, "id") is not None:
+                yield (key, getattr(value, "id"))
+            elif isinstance(value, list) or isinstance(value, tuple):
+                for i, sv in enumerate(value):
+                    # Always use indexed format for arrays
+                    encoded_key = "%s[%d]" % (key, i)
+                    if isinstance(sv, dict):
+                        subdict = _encode_nested_dict(encoded_key, sv)
+                        for k, v in _api_encode(subdict):
+                            yield (k, v)
+                    else:
+                        yield (encoded_key, sv)
+            elif isinstance(value, dict):
+                subdict = _encode_nested_dict(key, value)
+                for subkey, subvalue in _api_encode(subdict):
+                    yield (subkey, subvalue)
+            elif isinstance(value, datetime.datetime):
+                yield (key, _encode_datetime(value))
+            elif isinstance(value, bool):
+                yield (key, str(value).lower())
+            else:
+                yield (key, value)
diff --git a/tests/test_encode.py b/tests/test_encode.py
new file mode 100644
index 000000000..6aabc5c55
--- /dev/null
+++ b/tests/test_encode.py
@@ -0,0 +1,96 @@
+import warnings
+
+from stripe._stripe_object import StripeObject
+from stripe._encode import _api_encode
+
+
+class TestApiEncode:
+    def test_encode_stripe_object_without_id_no_deprecation_warning(self):
+        """
+        Test that encoding a StripeObject without an id (like metadata)
+        does not trigger a deprecation warning.
+        Regression test for issue #1651.
+        """
+        metadata = StripeObject()
+        metadata["key1"] = "value1"
+        metadata["key2"] = "value2"
+
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            result = list(_api_encode({"metadata": metadata}))
+
+            # Check no deprecation warnings were raised
+            deprecation_warnings = [
+                warning
+                for warning in w
+                if issubclass(warning.category, DeprecationWarning)
+            ]
+            assert len(deprecation_warnings) == 0, (
+                f"Expected no deprecation warnings, but got {len(deprecation_warnings)}"
+            )
+
+        # Verify the metadata was encoded correctly as nested dict
+        assert result == [
+            ("metadata[key1]", "value1"),
+            ("metadata[key2]", "value2"),
+        ]
+
+    def test_encode_stripe_object_with_id_extracts_id(self):
+        """
+        Test that encoding a StripeObject with an id (like a customer reference)
+        correctly extracts just the id value.
+        """
+        customer = StripeObject()
+        customer["id"] = "cus_123"
+        customer["name"] = "Test Customer"
+
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            result = list(_api_encode({"customer": customer}))
+
+            # Check no deprecation warnings were raised
+            deprecation_warnings = [
+                warning
+                for warning in w
+                if issubclass(warning.category, DeprecationWarning)
+            ]
+            assert len(deprecation_warnings) == 0, (
+                f"Expected no deprecation warnings, but got {len(deprecation_warnings)}"
+            )
+
+        # Should encode to just the ID
+        assert result == [("customer", "cus_123")]
+
+    def test_encode_regular_dict(self):
+        """Test that regular dicts are encoded as nested dicts."""
+        regular_dict = {"key1": "value1", "key2": "value2"}
+        result = list(_api_encode({"data": regular_dict}))
+
+        assert result == [
+            ("data[key1]", "value1"),
+            ("data[key2]", "value2"),
+        ]
+
+    def test_encode_none_value_skipped(self):
+        """Test that None values are skipped during encoding."""
+        result = list(_api_encode({"field": None}))
+        assert result == []
+
+    def test_encode_string_value(self):
+        """Test that string values are encoded directly."""
+        result = list(_api_encode({"name": "John Doe"}))
+        assert result == [("name", "John Doe")]
+
+    def test_encode_boolean_value(self):
+        """Test that boolean values are encoded as lowercase strings."""
+        result = list(_api_encode({"active": True, "deleted": False}))
+        assert result == [("active", "true"), ("deleted", "false")]
+
+    def test_encode_list_value(self):
+        """Test that list values are encoded with indexed keys."""
+        result = list(_api_encode({"items": ["item1", "item2", "item3"]}))
+        assert result == [
+            ("items[0]", "item1"),
+            ("items[1]", "item2"),
+            ("items[2]", "item3"),
+        ]