diff --git a/opensearch/connection/base.py b/opensearch/connection/base.py
index 05d81c71..b8c27237 100644
--- a/opensearch/connection/base.py
+++ b/opensearch/connection/base.py
@@ -28,6 +28,7 @@ import binascii
 import gzip
 import io
 import logging
+import os
 import re
 import warnings
 from platform import python_version
@@ -127,6 +128,11 @@ class Connection(object):
         if opaque_id:
             self.headers["x-opaque-id"] = opaque_id
 
+        if os.getenv("ELASTIC_CLIENT_APIVERSIONING") == "1":
+            self.headers.setdefault(
+                "accept", "application/vnd.elasticsearch+json;compatible-with=7"
+            )
+
         self.headers.setdefault("content-type", "application/json")
         self.headers.setdefault("user-agent", self._get_default_user_agent())
 
diff --git a/opensearch/serializer.py b/opensearch/serializer.py
index fcc9b146..d7180e8e 100644
--- a/opensearch/serializer.py
+++ b/opensearch/serializer.py
@@ -163,6 +163,11 @@ class Deserializer(object):
         if not mimetype:
             deserializer = self.default
         else:
+            # Treat 'application/vnd.elasticsearch+json'
+            # as application/json for compatibility.
+            if mimetype == "application/vnd.elasticsearch+json":
+                mimetype = "application/json"
+
             # split out charset
             mimetype, _, _ = mimetype.partition(";")
             try:
diff --git a/test_opensearch/test_connection.py b/test_opensearch/test_connection.py
index c02a7183..e296a29b 100644
--- a/test_opensearch/test_connection.py
+++ b/test_opensearch/test_connection.py
@@ -28,6 +28,7 @@
 import gzip
 import io
 import json
+import os
 import re
 import ssl
 import warnings
@@ -173,6 +174,26 @@ class TestBaseConnection(TestCase):
             conn = Connection(**kwargs)
             assert conn.host == expected_host
 
+    def test_compatibility_accept_header(self):
+        try:
+            conn = Connection()
+            assert "accept" not in conn.headers
+
+            os.environ["ELASTIC_CLIENT_APIVERSIONING"] = "0"
+
+            conn = Connection()
+            assert "accept" not in conn.headers
+
+            os.environ["ELASTIC_CLIENT_APIVERSIONING"] = "1"
+
+            conn = Connection()
+            assert (
+                conn.headers["accept"]
+                == "application/vnd.elasticsearch+json;compatible-with=7"
+            )
+        finally:
+            os.environ.pop("ELASTIC_CLIENT_APIVERSIONING")
+
 
 class TestUrllib3Connection(TestCase):
     def _get_mock_connection(self, connection_params={}, response_body=b"{}"):