diff --git a/elasticsearch_serverless/_sync/client/utils.py b/elasticsearch_serverless/_sync/client/utils.py
index ad890a4..0c92fc3 100644
--- a/elasticsearch_serverless/_sync/client/utils.py
+++ b/elasticsearch_serverless/_sync/client/utils.py
@@ -60,6 +60,7 @@
 
 # Default User-Agent used by the client
 USER_AGENT = create_user_agent("elasticsearch-py", __versionstr__)
+ELASTIC_API_VERSION = "2023-10-31"
 
 _TYPE_HOST = Union[str, Mapping[str, Union[str, int]], NodeConfig]
 
@@ -97,6 +98,8 @@ def client_node_config(
     # Set the 'User-Agent' default header.
     headers = HttpHeaders(node_options.pop("headers", ()))
     headers.setdefault("user-agent", USER_AGENT)
+    headers.setdefault("elastic-api-version", ELASTIC_API_VERSION)
+
     node_options["headers"] = headers
 
     # If a custom Requests AuthBase is passed we set that via '_extras'.
@@ -112,6 +115,8 @@ def client_node_config(
         headers.update(headers_to_add)
 
     headers.setdefault("user-agent", USER_AGENT)
+    headers.setdefault("elastic-api-version", ELASTIC_API_VERSION)
+
     headers.freeze()
     node_options["headers"] = headers
 
diff --git a/test_elasticsearch_serverless/test_client/test_options.py b/test_elasticsearch_serverless/test_client/test_options.py
index 8fa2cbe..94a5051 100644
--- a/test_elasticsearch_serverless/test_client/test_options.py
+++ b/test_elasticsearch_serverless/test_client/test_options.py
@@ -20,7 +20,7 @@
 from elastic_transport.client_utils import DEFAULT
 
 from elasticsearch_serverless import AsyncElasticsearch, Elasticsearch
-from elasticsearch_serverless._sync.client.utils import USER_AGENT
+from elasticsearch_serverless._sync.client.utils import ELASTIC_API_VERSION, USER_AGENT
 from test_elasticsearch_serverless.test_cases import (
     DummyAsyncTransport,
     DummyTransport,
@@ -279,7 +279,10 @@ def test_default_node_configs(self):
         assert node_config.host == "localhost"
         assert node_config.port == 9200
         assert node_config.path_prefix == ""
-        assert node_config.headers == {"user-agent": USER_AGENT}
+        assert node_config.headers == {
+            "user-agent": USER_AGENT,
+            "elastic-api-version": ELASTIC_API_VERSION,
+        }
 
     def test_http_headers_overrides(self):
         client = Elasticsearch(
@@ -324,6 +327,7 @@ def test_http_headers_overrides(self):
         assert node_config.headers == {
             "authorization": "Basic dXNlcm5hbWU6cGFzc3dvcmQ=",
             "user-agent": USER_AGENT,
+            "elastic-api-version": ELASTIC_API_VERSION,
         }
         assert client._headers == {"key": "val"}
 
diff --git a/test_elasticsearch_serverless/test_transport.py b/test_elasticsearch_serverless/test_transport.py
index 66328ab..1e8cc85 100644
--- a/test_elasticsearch_serverless/test_transport.py
+++ b/test_elasticsearch_serverless/test_transport.py
@@ -25,6 +25,7 @@
 from elastic_transport.client_utils import DEFAULT
 
 from elasticsearch_serverless import Elasticsearch, __versionstr__
+from elasticsearch_serverless._sync.client import utils
 from elasticsearch_serverless.exceptions import (
     ApiError,
     ConnectionError,
@@ -189,8 +190,9 @@ def test_custom_user_agent_on_initialization(self):
             "http://localhost:9200", headers={"user-agent": "custom/1.2.3"}
         )
         headers = [node.config for node in client.transport.node_pool.all()][0].headers
-        assert list(headers.keys()) == ["user-agent"]
+        assert list(headers.keys()) == ["user-agent", "elastic-api-version"]
         assert headers["user-agent"].startswith(f"elasticsearch-py/{__versionstr__} (")
+        assert headers["elastic-api-version"] == utils.ELASTIC_API_VERSION
 
     def test_request_with_custom_user_agent_header(self):
         client = Elasticsearch(