diff --git a/api/environments/models.py b/api/environments/models.py
index d872645c6d14..17eb27999ca3 100644
--- a/api/environments/models.py
+++ b/api/environments/models.py
@@ -165,7 +165,9 @@ def create_feature_states(self) -> None:
     @hook(AFTER_UPDATE)  # type: ignore[misc]
     def clear_environment_cache(self) -> None:
         # TODO: this could rebuild the cache itself (using an async task)
-        environment_cache.delete(self.initial_value("api_key"))
+        environment_cache.delete_many(
+            [self.initial_value("api_key"), *[eak.key for eak in self.api_keys.all()]]
+        )
 
     @hook(AFTER_UPDATE, when="api_key", has_changed=True)  # type: ignore[misc]
     def update_environment_document_cache(self) -> None:
diff --git a/api/environments/sdk/views.py b/api/environments/sdk/views.py
index acba8cf94bef..ad73b8e3d45f 100644
--- a/api/environments/sdk/views.py
+++ b/api/environments/sdk/views.py
@@ -1,15 +1,27 @@
-from django.http import HttpRequest
+from datetime import datetime
+from typing import Optional
+
+from django.utils.decorators import method_decorator
+from django.views.decorators.http import condition
 from drf_yasg.utils import swagger_auto_schema  # type: ignore[import-untyped]
+from rest_framework.request import Request
 from rest_framework.response import Response
 from rest_framework.views import APIView
 
 from core.constants import FLAGSMITH_UPDATED_AT_HEADER
-from environments.authentication import EnvironmentKeyAuthentication
+from environments.authentication import (
+    EnvironmentKeyAuthentication,
+)
 from environments.models import Environment
 from environments.permissions.permissions import EnvironmentKeyPermissions
 from environments.sdk.schemas import SDKEnvironmentDocumentModel
 
 
+def get_last_modified(request: Request) -> datetime | None:
+    updated_at: Optional[datetime] = request.environment.updated_at
+    return updated_at
+
+
 class SDKEnvironmentAPIView(APIView):
     permission_classes = (EnvironmentKeyPermissions,)
     throttle_classes = []
@@ -18,9 +30,10 @@ def get_authenticators(self):  # type: ignore[no-untyped-def]
         return [EnvironmentKeyAuthentication(required_key_prefix="ser.")]
 
     @swagger_auto_schema(responses={200: SDKEnvironmentDocumentModel})  # type: ignore[misc]
-    def get(self, request: HttpRequest) -> Response:
+    @method_decorator(condition(last_modified_func=get_last_modified))
+    def get(self, request: Request) -> Response:
         environment_document = Environment.get_environment_document(
-            request.environment.api_key  # type: ignore[attr-defined]
+            request.environment.api_key,
         )
         updated_at = self.request.environment.updated_at
         return Response(
diff --git a/api/tests/unit/environments/test_unit_environments_models.py b/api/tests/unit/environments/test_unit_environments_models.py
index 55c068fcb621..0aa5abb336cc 100644
--- a/api/tests/unit/environments/test_unit_environments_models.py
+++ b/api/tests/unit/environments/test_unit_environments_models.py
@@ -408,9 +408,9 @@ def test_save_environment_clears_environment_cache(mocker, project):  # type: ig
     environment.save()
 
     # Then
-    mock_calls = mock_environment_cache.delete.mock_calls
+    mock_calls = mock_environment_cache.delete_many.mock_calls
     assert len(mock_calls) == 2
-    assert mock_calls[0][1][0] == mock_calls[1][1][0] == old_key
+    assert mock_calls[0][1][0] == mock_calls[1][1][0] == [old_key]
 
 
 @pytest.mark.parametrize(
diff --git a/api/tests/unit/environments/test_unit_environments_views_sdk_environment.py b/api/tests/unit/environments/test_unit_environments_views_sdk_environment.py
index f28a40ecb729..556156dc2ade 100644
--- a/api/tests/unit/environments/test_unit_environments_views_sdk_environment.py
+++ b/api/tests/unit/environments/test_unit_environments_views_sdk_environment.py
@@ -1,7 +1,10 @@
+import time
 from typing import TYPE_CHECKING
 
 import pytest
 from django.urls import reverse
+from django.utils import timezone
+from django.utils.http import http_date
 from flag_engine.segments.constants import EQUAL
 from rest_framework import status
 from rest_framework.test import APIClient
@@ -175,3 +178,62 @@ def test_get_environment_document_fails_with_invalid_key(
     # We get a 403 since only the server side API keys are able to access the
     # environment document
     assert response.status_code == status.HTTP_403_FORBIDDEN
+
+
+def test_environment_document_if_modified_since(
+    organisation_one: "Organisation",
+    organisation_one_project_one: "Project",
+) -> None:
+    # Given
+    project = organisation_one_project_one
+    environment = Environment.objects.create(name="Test Environment", project=project)
+    api_key = EnvironmentAPIKey.objects.create(environment=environment).key
+
+    client = APIClient()
+    client.credentials(HTTP_X_ENVIRONMENT_KEY=api_key)
+    url = reverse("api-v1:environment-document")
+
+    # When - first request
+    response1 = client.get(url)
+
+    # Then - first request should return 200 and include Last-Modified header
+    assert response1.status_code == status.HTTP_200_OK
+    last_modified = response1.headers["Last-Modified"]
+    assert last_modified == http_date(environment.updated_at.timestamp())
+
+    # When - second request with If-Modified-Since header
+    client.credentials(
+        HTTP_X_ENVIRONMENT_KEY=api_key,
+        HTTP_IF_MODIFIED_SINCE=last_modified,
+    )
+    response2 = client.get(url)
+
+    # Then - second request should return 304 Not Modified
+    assert response2.status_code == status.HTTP_304_NOT_MODIFIED
+    assert len(response2.content) == 0
+
+    # sleep for 1s since If-Modified-Since is only accurate to the nearest second
+    # https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/If-Modified-Since
+    time.sleep(1)
+
+    # When - environment is updated
+    environment.updated_at = timezone.now()
+    environment.save()
+
+    # Then - request with same If-Modified-Since header should return 200
+    response3 = client.get(url)
+    assert response3.status_code == status.HTTP_200_OK
+    assert response3.headers["Last-Modified"] == http_date(
+        environment.updated_at.timestamp()
+    )
+
+    # When - request without If-Modified-Since header
+    client.credentials(
+        HTTP_X_ENVIRONMENT_KEY=api_key,
+        HTTP_IF_MODIFIED_SINCE="",
+    )
+    response4 = client.get(url)
+
+    # Then - actual environment is returned with a 200
+    assert response4.status_code == status.HTTP_200_OK
+    assert len(response4.content) > 0
diff --git a/api/tests/unit/integrations/amplitude/test_unit_amplitude_models.py b/api/tests/unit/integrations/amplitude/test_unit_amplitude_models.py
index 86c6214ab42b..e858319e4a0a 100644
--- a/api/tests/unit/integrations/amplitude/test_unit_amplitude_models.py
+++ b/api/tests/unit/integrations/amplitude/test_unit_amplitude_models.py
@@ -60,4 +60,4 @@ def test_amplitude_configuration_update_clears_environment_cache(environment, mo
     amplitude_config.save()
 
     # Then
-    mock_environment_cache.delete.assert_called_once_with(environment.api_key)
+    mock_environment_cache.delete_many.assert_called_once_with([environment.api_key])