diff --git a/contract-tests/client_entity.py b/contract-tests/client_entity.py
index 8b0c097f..02c44aba 100644
--- a/contract-tests/client_entity.py
+++ b/contract-tests/client_entity.py
@@ -27,12 +27,16 @@ def __init__(self, tag, config):
             streaming = config["streaming"]
             if streaming.get("baseUri") is not None:
                 opts["stream_uri"] = streaming["baseUri"]
+            if streaming.get("filter") is not None:
+                opts["payload_filter_key"] = streaming["filter"]
             _set_optional_time_prop(streaming, "initialRetryDelayMs", opts, "initial_reconnect_delay")
         else:
             opts['stream'] = False
             polling = config["polling"]
             if polling.get("baseUri") is not None:
                 opts["base_uri"] = polling["baseUri"]
+            if polling.get("filter") is not None:
+                opts["payload_filter_key"] = polling["filter"]
             _set_optional_time_prop(polling, "pollIntervalMs", opts, "poll_interval")
 
         if config.get("events") is not None:
diff --git a/contract-tests/service.py b/contract-tests/service.py
index be7ef23f..ffa6d3e2 100644
--- a/contract-tests/service.py
+++ b/contract-tests/service.py
@@ -65,6 +65,7 @@ def status():
             'all-flags-details-only-for-tracked-flags',
             'big-segments',
             'context-type',
+            'filtering',
             'secure-mode-hash',
             'tags',
             'migrations',
diff --git a/ldclient/config.py b/ldclient/config.py
index 59248996..d73001cc 100644
--- a/ldclient/config.py
+++ b/ldclient/config.py
@@ -182,6 +182,7 @@ def __init__(
         hooks: Optional[List[Hook]] = None,
         enable_event_compression: bool = False,
         omit_anonymous_contexts: bool = False,
+        payload_filter_key: Optional[str] = None,
     ):
         """
         :param sdk_key: The SDK key for your LaunchDarkly account. This is always required.
@@ -250,6 +251,7 @@ def __init__(
         :param hooks: Hooks provide entrypoints which allow for observation of SDK functions.
         :param enable_event_compression: Whether or not to enable GZIP compression for outgoing events.
         :param omit_anonymous_contexts: Sets whether anonymous contexts should be omitted from index and identify events.
+        :param payload_filter_key: The payload filter is used to selectively limited the flags and segments delivered in the data source payload.
         """
         self.__sdk_key = sdk_key
 
@@ -285,6 +287,7 @@ def __init__(
         self.__hooks = [hook for hook in hooks if isinstance(hook, Hook)] if hooks else []
         self.__enable_event_compression = enable_event_compression
         self.__omit_anonymous_contexts = omit_anonymous_contexts
+        self.__payload_filter_key = payload_filter_key
         self._data_source_update_sink: Optional[DataSourceUpdateSink] = None
 
     def copy_with_new_sdk_key(self, new_sdk_key: str) -> 'Config':
@@ -484,6 +487,26 @@ def omit_anonymous_contexts(self) -> bool:
         """
         return self.__omit_anonymous_contexts
 
+    @property
+    def payload_filter_key(self) -> Optional[str]:
+        """
+       LaunchDarkly Server SDKs historically downloaded all flag configuration
+       and segments for a particular environment during initialization.
+
+       For some customers, this is an unacceptably large amount of data, and
+       has contributed to performance issues within their products.
+
+       Filtered environments aim to solve this problem. By allowing customers
+       to specify subsets of an environment's flags using a filter key, SDKs
+       will initialize faster and use less memory.
+
+       This payload filter key only applies to the default streaming and
+       polling data sources. It will not affect TestData or FileData data
+       sources, nor will it be applied to any data source provided through the
+       {#data_source} config property.
+        """
+        return self.__payload_filter_key
+
     @property
     def data_source_update_sink(self) -> Optional[DataSourceUpdateSink]:
         """
diff --git a/ldclient/impl/datasource/feature_requester.py b/ldclient/impl/datasource/feature_requester.py
index ac7a959e..83f044db 100644
--- a/ldclient/impl/datasource/feature_requester.py
+++ b/ldclient/impl/datasource/feature_requester.py
@@ -4,6 +4,7 @@
 
 import json
 from collections import namedtuple
+from urllib import parse
 
 import urllib3
 
@@ -24,6 +25,8 @@ def __init__(self, config):
         self._http = _http_factory(config).create_pool_manager(1, config.base_uri)
         self._config = config
         self._poll_uri = config.base_uri + LATEST_ALL_URI
+        if config.payload_filter_key is not None:
+            self._poll_uri += '?%s' % parse.urlencode({'filter': config.payload_filter_key})
 
     def get_all_data(self):
         uri = self._poll_uri
diff --git a/ldclient/impl/datasource/streaming.py b/ldclient/impl/datasource/streaming.py
index d4f89b59..eb3c6724 100644
--- a/ldclient/impl/datasource/streaming.py
+++ b/ldclient/impl/datasource/streaming.py
@@ -3,6 +3,7 @@
 from collections import namedtuple
 from threading import Thread
 from typing import Optional
+from urllib import parse
 
 from ld_eventsource import SSEClient
 from ld_eventsource.actions import Event, Fault
@@ -35,6 +36,8 @@ def __init__(self, config, store, ready, diagnostic_accumulator):
         Thread.__init__(self, name="ldclient.datasource.streaming")
         self.daemon = True
         self._uri = config.stream_base_uri + STREAM_ALL_PATH
+        if config.payload_filter_key is not None:
+            self._uri += '?%s' % parse.urlencode({'filter': config.payload_filter_key})
         self._config = config
         self._data_source_update_sink = config.data_source_update_sink
         self._store = store
diff --git a/ldclient/impl/http.py b/ldclient/impl/http.py
index 016ea5bc..27864fd8 100644
--- a/ldclient/impl/http.py
+++ b/ldclient/impl/http.py
@@ -1,5 +1,5 @@
 from os import environ
-from typing import Tuple
+from typing import Optional, Tuple
 from urllib.parse import urlparse
 
 import certifi