diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0ad9dba..20b8b1b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,9 +8,12 @@ and this project adheres to [Semantic Versioning].
 [Keep a Changelog]: https://keepachangelog.com/en/1.0.0/
 [Semantic Versioning]: https://semver.org/spec/v2.0.0.html
 
+## [4.9.0] - 2026-03-16
+- Add `external_id` key to Contact model
+
 ## [4.8.0] - 2026-01-06
 - Mention filters (CFL) param for metrics api
-- Add Customer.subscriptions 
+- Add Customer.subscriptions
 - Update CustomerSubscription.list_imported to deprecated
 - Add disabled, disabled_at, edit_history_summary and errors fields to Invoice
 
@@ -24,7 +27,7 @@ and this project adheres to [Semantic Versioning].
 - Remove future dependency to resolve vulnerability issues
 
 ## [4.6.2] - 2025-07-09
-- Update Marshmallow dependency to use >=3.24.0 
+- Update Marshmallow dependency to use >=3.24.0
 
 ## [4.6.1] - 2025-05-19
 - Fixed Tasks API schema issue
diff --git a/chartmogul/api/contact.py b/chartmogul/api/contact.py
index 6c1b8d1..92b0e24 100644
--- a/chartmogul/api/contact.py
+++ b/chartmogul/api/contact.py
@@ -26,6 +26,9 @@ class _Schema(Schema):
         phone = fields.String(allow_none=True)
         linked_in = fields.String(allow_none=True)
         twitter = fields.String(allow_none=True)
+        # load_default=None ensures this attribute is always present on the Contact
+        # object even when the API omits the field (e.g. older responses)
+        external_id = fields.String(allow_none=True, load_default=None)
         custom = fields.Dict(allow_none=True)
 
         @post_load
diff --git a/chartmogul/version.py b/chartmogul/version.py
index ea674c5..454a2ed 100644
--- a/chartmogul/version.py
+++ b/chartmogul/version.py
@@ -1 +1 @@
-__version__ = "4.8.0"
+__version__ = "4.9.0"
diff --git a/test/api/test_contact.py b/test/api/test_contact.py
index 3cd041c..9295414 100644
--- a/test/api/test_contact.py
+++ b/test/api/test_contact.py
@@ -9,6 +9,7 @@
     "customer_uuid": "cus_00000000-0000-0000-0000-000000000000",
     "data_source_uuid": "ds_00000000-0000-0000-0000-000000000000",
     "customer_external_id": "external_001",
+    "external_id": "contact_external_id_001",
     "first_name": "First name",
     "last_name": "Last name",
     "position": 9,
@@ -25,6 +26,7 @@
     "uuid": "con_00000000-0000-0000-0000-000000000000",
     "customer_uuid": "cus_00000000-0000-0000-0000-000000000000",
     "data_source_uuid": "ds_00000000-0000-0000-0000-000000000000",
+    "external_id": "contact_external_id_001",
     "first_name": "First name",
     "last_name": "Last name",
     "position": 9,
@@ -42,6 +44,18 @@
 
 allContacts = {"entries": [contact], "cursor": "cursor==", "has_more": False}
 
+contactWithoutExternalId = {k: v for k, v in contact.items() if k != "external_id"}
+
+contactWithNullExternalId = {
+    **contact,
+    "external_id": None,
+}
+
+createContactWithNullExternalId = {
+    **createContact,
+    "external_id": None,
+}
+
 
 class ContactTestCase(unittest.TestCase):
     """
@@ -93,6 +107,30 @@ def test_create(self, mock_requests):
         self.assertEqual(mock_requests.last_request.qs, {})
         self.assertEqual(mock_requests.last_request.json(), createContact)
 
+    @requests_mock.mock()
+    def test_create_with_null_external_id(self, mock_requests):
+        mock_requests.register_uri(
+            "POST", "https://api.chartmogul.com/v1/contacts", status_code=200, json=contactWithNullExternalId
+        )
+
+        config = Config("token")
+        result = Contact.create(config, data=createContactWithNullExternalId).get()
+        self.assertEqual(mock_requests.call_count, 1, "expected call")
+        self.assertEqual(mock_requests.last_request.json(), createContactWithNullExternalId)
+        self.assertIsNone(result.external_id)
+
+    @requests_mock.mock()
+    def test_create_without_external_id(self, mock_requests):
+        mock_requests.register_uri(
+            "POST", "https://api.chartmogul.com/v1/contacts", status_code=200, json=contactWithoutExternalId
+        )
+
+        config = Config("token")
+        result = Contact.create(config, data=createContactWithNullExternalId).get()
+        self.assertEqual(mock_requests.call_count, 1, "expected call")
+        self.assertEqual(mock_requests.last_request.json(), createContactWithNullExternalId)
+        self.assertIsNone(result.external_id)
+
     @requests_mock.mock()
     def test_merge(self, mock_requests):
         mock_requests.register_uri(
@@ -133,6 +171,24 @@ def test_modify(self, mock_requests):
         self.assertEqual(mock_requests.last_request.json(), jsonRequest)
         self.assertTrue(isinstance(expected, Contact))
 
+    @requests_mock.mock()
+    def test_modify_with_null_external_id(self, mock_requests):
+        mock_requests.register_uri(
+            "PATCH",
+            "https://api.chartmogul.com/v1/contacts/con_00000000-0000-0000-0000-000000000000",
+            status_code=200,
+            json=contactWithNullExternalId,
+        )
+
+        jsonRequest = {"external_id": None}
+        config = Config("token")
+        result = Contact.modify(
+            config, uuid="con_00000000-0000-0000-0000-000000000000", data=jsonRequest
+        ).get()
+        self.assertEqual(mock_requests.call_count, 1, "expected call")
+        self.assertEqual(mock_requests.last_request.json(), jsonRequest)
+        self.assertIsNone(result.external_id)
+
     @requests_mock.mock()
     def test_retrieve(self, mock_requests):
         mock_requests.register_uri(