diff --git a/lib/ldclient-rb/config.rb b/lib/ldclient-rb/config.rb
index c324c02b..28d4b20c 100644
--- a/lib/ldclient-rb/config.rb
+++ b/lib/ldclient-rb/config.rb
@@ -18,6 +18,8 @@ class Config
     #
     # @param opts [Hash] the configuration options
     # @option opts [Logger] :logger See {#logger}.
+    # @option opts [String] :base_uri ("https://sdk.launchdarkly.com") See {#base_uri}.
+    # @option opts [String] :stream_uri ("https://stream.launchdarkly.com") See {#stream_uri}.
     # @option opts [String] :events_uri ("https://events.launchdarkly.com") See {#events_uri}.
     # @option opts [Integer] :capacity (10000) See {#capacity}.
     # @option opts [Float] :flush_interval (30) See {#flush_interval}.
@@ -42,6 +44,8 @@ class Config
     # @option plugins [Array<Interfaces::Plugins::Plugin]
     #
     def initialize(opts = {})
+      @base_uri = (opts[:base_uri] || Config.default_base_uri).chomp("/")
+      @stream_uri = (opts[:stream_uri] || Config.default_stream_uri).chomp("/")
       @events_uri = (opts[:events_uri] || Config.default_events_uri).chomp("/")
       @capacity = opts[:capacity] || Config.default_capacity
       @logger = opts[:logger] || Config.default_logger
@@ -82,6 +86,22 @@ def initialize(opts = {})
     #
     attr_accessor :instance_id
 
+    #
+    # The base URL for the LaunchDarkly polling service. The polling data sources use it unless
+    # their builder sets a base URI. Set it to the URL of a Relay Proxy instance to get flag data
+    # from the Relay Proxy.
+    # @return [String]
+    #
+    attr_reader :base_uri
+
+    #
+    # The base URL for the LaunchDarkly streaming service. The streaming data source uses it unless
+    # its builder sets a base URI. Set it to the URL of a Relay Proxy instance to get flag data
+    # from the Relay Proxy.
+    # @return [String]
+    #
+    attr_reader :stream_uri
+
     #
     # The base URL for the LaunchDarkly events server. This is configurable mainly for testing
     # purposes; most users should use the default value.
@@ -351,6 +371,22 @@ def self.default_capacity
       10000
     end
 
+    #
+    # The default value for {#base_uri}.
+    # @return [String] "https://sdk.launchdarkly.com"
+    #
+    def self.default_base_uri
+      DataSystem::PollingDataSourceBuilder::DEFAULT_BASE_URI
+    end
+
+    #
+    # The default value for {#stream_uri}.
+    # @return [String] "https://stream.launchdarkly.com"
+    #
+    def self.default_stream_uri
+      DataSystem::StreamingDataSourceBuilder::DEFAULT_BASE_URI
+    end
+
     #
     # The default value for {#events_uri}.
     # @return [String] "https://events.launchdarkly.com"
diff --git a/lib/ldclient-rb/data_system.rb b/lib/ldclient-rb/data_system.rb
index dd03b511..4ff661b8 100644
--- a/lib/ldclient-rb/data_system.rb
+++ b/lib/ldclient-rb/data_system.rb
@@ -35,6 +35,18 @@ module LaunchDarkly
   #     data_system: LaunchDarkly::DataSystem.polling
   #   )
   #
+  # == Relay Proxy
+  #
+  # Every data source uses the URIs from the SDK configuration, unless its builder
+  # sets a base URI. To get data from a Relay Proxy instance, set the URIs in the
+  # SDK configuration:
+  #
+  #   config = LaunchDarkly::Config.new(
+  #     base_uri: "https://relay.example.com",
+  #     stream_uri: "https://relay.example.com",
+  #     events_uri: "https://relay.example.com"
+  #   )
+  #
   # == Custom Configurations
   #
   # For advanced use cases, you can build custom configurations using the
diff --git a/lib/ldclient-rb/data_system/data_source_builder_common.rb b/lib/ldclient-rb/data_system/data_source_builder_common.rb
index c264fc61..23ec96be 100644
--- a/lib/ldclient-rb/data_system/data_source_builder_common.rb
+++ b/lib/ldclient-rb/data_system/data_source_builder_common.rb
@@ -11,15 +11,22 @@ module DataSystem
     # {FDv1PollingDataSourceBuilder}, and {StreamingDataSourceBuilder} to provide
     # a consistent set of HTTP connection settings.
     #
-    # Each builder that includes this module must define a +DEFAULT_BASE_URI+ constant
-    # which is used as the fallback when {#base_uri} has not been called.
+    # A setting that the builder does not set comes from the SDK configuration. The
+    # base URI comes from {LaunchDarkly::Config#base_uri} for the polling builders and
+    # from {LaunchDarkly::Config#stream_uri} for the streaming builder. The socket factory
+    # and the timeouts come from {LaunchDarkly::Config#socket_factory},
+    # {LaunchDarkly::Config#read_timeout} and {LaunchDarkly::Config#connect_timeout}.
+    #
+    # Each builder that includes this module must define a private +config_base_uri+
+    # method that returns the base URI from the SDK configuration.
     #
     module DataSourceBuilderCommon
       #
       # Sets the base URI for HTTP requests.
       #
       # Use this to point the SDK at a Relay Proxy instance or any other URI
-      # that implements the corresponding LaunchDarkly API.
+      # that implements the corresponding LaunchDarkly API. This value overrides
+      # the base URI in the SDK configuration.
       #
       # @param uri [String] The base URI (e.g. "https://relay.example.com")
       # @return [self] the builder, for chaining
@@ -31,6 +38,7 @@ def base_uri(uri)
 
       #
       # Sets a custom socket factory for HTTP connections.
+      # This value overrides {LaunchDarkly::Config#socket_factory}.
       #
       # @param factory [#open] A socket factory that responds to +open+
       # @return [self] the builder, for chaining
@@ -42,6 +50,7 @@ def socket_factory(factory)
 
       #
       # Sets the read timeout for HTTP connections.
+      # This value overrides {LaunchDarkly::Config#read_timeout}.
       #
       # @param timeout [Float] Timeout in seconds
       # @return [self] the builder, for chaining
@@ -53,6 +62,7 @@ def read_timeout(timeout)
 
       #
       # Sets the connect timeout for HTTP connections.
+      # This value overrides {LaunchDarkly::Config#connect_timeout}.
       #
       # @param timeout [Float] Timeout in seconds
       # @return [self] the builder, for chaining
@@ -63,18 +73,18 @@ def connect_timeout(timeout)
       end
 
       #
-      # Builds an HttpConfigOptions instance from the current builder settings.
-      # Uses +self.class::DEFAULT_BASE_URI+ if {#base_uri} was not explicitly set.
-      # Read/connect timeouts default to HttpConfigOptions defaults if not set.
+      # Builds an HttpConfigOptions instance from the builder settings. A setting
+      # that the builder does not set comes from the SDK configuration.
       #
+      # @param config [LaunchDarkly::Config] the SDK configuration
       # @return [LaunchDarkly::Impl::DataSystem::HttpConfigOptions]
       #
-      private def build_http_config
+      private def build_http_config(config)
         LaunchDarkly::Impl::DataSystem::HttpConfigOptions.new(
-          base_uri: (@base_uri || self.class::DEFAULT_BASE_URI).chomp("/"),
-          socket_factory: @socket_factory,
-          read_timeout: @read_timeout,
-          connect_timeout: @connect_timeout
+          base_uri: (@base_uri || config_base_uri(config)).chomp("/"),
+          socket_factory: @socket_factory || config.socket_factory,
+          read_timeout: @read_timeout || config.read_timeout,
+          connect_timeout: @connect_timeout || config.connect_timeout
         )
       end
     end
diff --git a/lib/ldclient-rb/data_system/polling_data_source_builder.rb b/lib/ldclient-rb/data_system/polling_data_source_builder.rb
index d2ea1d95..7b386e3d 100644
--- a/lib/ldclient-rb/data_system/polling_data_source_builder.rb
+++ b/lib/ldclient-rb/data_system/polling_data_source_builder.rb
@@ -153,10 +153,14 @@ def requester(requester)
       # @return [LaunchDarkly::Impl::DataSystem::PollingDataSource]
       #
       def build(sdk_key, config)
-        http_opts = build_http_config
+        http_opts = build_http_config(config)
         requester = @requester || LaunchDarkly::Impl::DataSystem::HTTPPollingRequester.new(sdk_key, http_opts, config)
         LaunchDarkly::Impl::DataSystem::PollingDataSource.new(effective_poll_interval(config.logger), requester, config.logger)
       end
+
+      private def config_base_uri(config)
+        config.base_uri
+      end
     end
 
     #
@@ -238,10 +242,14 @@ def requester(requester)
       # @return [LaunchDarkly::Impl::DataSystem::PollingDataSource]
       #
       def build(sdk_key, config)
-        http_opts = build_http_config
+        http_opts = build_http_config(config)
         requester = @requester || LaunchDarkly::Impl::DataSystem::HTTPFDv1PollingRequester.new(sdk_key, http_opts, config)
         LaunchDarkly::Impl::DataSystem::PollingDataSource.new(effective_poll_interval(config.logger), requester, config.logger)
       end
+
+      private def config_base_uri(config)
+        config.base_uri
+      end
     end
   end
 end
diff --git a/lib/ldclient-rb/data_system/streaming_data_source_builder.rb b/lib/ldclient-rb/data_system/streaming_data_source_builder.rb
index 7fdcf44b..1617a98d 100644
--- a/lib/ldclient-rb/data_system/streaming_data_source_builder.rb
+++ b/lib/ldclient-rb/data_system/streaming_data_source_builder.rb
@@ -61,13 +61,17 @@ def initial_reconnect_delay(delay)
       # @return [LaunchDarkly::Impl::DataSystem::StreamingDataSource]
       #
       def build(sdk_key, config)
-        http_opts = build_http_config
+        http_opts = build_http_config(config)
         LaunchDarkly::Impl::DataSystem::StreamingDataSource.new(
           sdk_key, http_opts,
           @initial_reconnect_delay || DEFAULT_INITIAL_RECONNECT_DELAY,
           config
         )
       end
+
+      private def config_base_uri(config)
+        config.stream_uri
+      end
     end
   end
 end
diff --git a/spec/config_spec.rb b/spec/config_spec.rb
index 950fc7af..403fba76 100644
--- a/spec/config_spec.rb
+++ b/spec/config_spec.rb
@@ -13,6 +13,22 @@ module LaunchDarkly
         expect(subject.new(capacity: 50).capacity).to eq 50
       end
     end
+    describe ".base_uri" do
+      it "defaults to the LaunchDarkly polling service" do
+        expect(subject.new.base_uri).to eq "https://sdk.launchdarkly.com"
+      end
+      it "can be set and removes a trailing slash" do
+        expect(subject.new(base_uri: "https://relay.example.com/").base_uri).to eq "https://relay.example.com"
+      end
+    end
+    describe ".stream_uri" do
+      it "defaults to the LaunchDarkly streaming service" do
+        expect(subject.new.stream_uri).to eq "https://stream.launchdarkly.com"
+      end
+      it "can be set and removes a trailing slash" do
+        expect(subject.new(stream_uri: "https://relay.example.com/").stream_uri).to eq "https://relay.example.com"
+      end
+    end
     describe "@events_uri" do
       it "can be read" do
         expect(subject.new.events_uri).to eq subject.default_events_uri
diff --git a/spec/data_system/data_source_builder_common_spec.rb b/spec/data_system/data_source_builder_common_spec.rb
new file mode 100644
index 00000000..ed2f5ed4
--- /dev/null
+++ b/spec/data_system/data_source_builder_common_spec.rb
@@ -0,0 +1,73 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+module LaunchDarkly
+  module DataSystem
+    {
+      PollingDataSourceBuilder => :base_uri,
+      FDv1PollingDataSourceBuilder => :base_uri,
+      StreamingDataSourceBuilder => :stream_uri,
+    }.each do |builder_class, uri_option|
+      RSpec.describe builder_class do
+        let(:socket_factory) { double("socket factory") }
+
+        def http_config_of(builder, config)
+          http_config = nil
+          allow(Impl::DataSystem::HttpConfigOptions).to receive(:new).and_wrap_original do |original, **args|
+            http_config = original.call(**args)
+          end
+          builder.build("sdk-key", config)
+          http_config
+        end
+
+        it "uses the default URI and HTTP options" do
+          config = Config.new(logger: $null_log)
+          http_config = http_config_of(described_class.new, config)
+
+          expect(http_config.base_uri).to eq described_class::DEFAULT_BASE_URI
+          expect(http_config.socket_factory).to be_nil
+          expect(http_config.read_timeout).to eq Config.default_read_timeout
+          expect(http_config.connect_timeout).to eq Config.default_connect_timeout
+        end
+
+        it "uses the URI and HTTP options from the SDK configuration" do
+          config = Config.new(
+            logger: $null_log,
+            uri_option => "https://relay.example.com/",
+            socket_factory: socket_factory,
+            read_timeout: 15,
+            connect_timeout: 4
+          )
+          http_config = http_config_of(described_class.new, config)
+
+          expect(http_config.base_uri).to eq "https://relay.example.com"
+          expect(http_config.socket_factory).to be socket_factory
+          expect(http_config.read_timeout).to eq 15
+          expect(http_config.connect_timeout).to eq 4
+        end
+
+        it "uses the builder settings in place of the SDK configuration" do
+          config = Config.new(
+            logger: $null_log,
+            uri_option => "https://relay.example.com",
+            socket_factory: double("config socket factory"),
+            read_timeout: 15,
+            connect_timeout: 4
+          )
+          builder = described_class.new
+            .base_uri("https://builder.example.com/")
+            .socket_factory(socket_factory)
+            .read_timeout(20)
+            .connect_timeout(6)
+          http_config = http_config_of(builder, config)
+
+          expect(http_config.base_uri).to eq "https://builder.example.com"
+          expect(http_config.socket_factory).to be socket_factory
+          expect(http_config.read_timeout).to eq 20
+          expect(http_config.connect_timeout).to eq 6
+        end
+      end
+    end
+  end
+end
diff --git a/spec/impl/data_system/streaming_headers_spec.rb b/spec/impl/data_system/streaming_headers_spec.rb
index 6da13874..42a0cc05 100644
--- a/spec/impl/data_system/streaming_headers_spec.rb
+++ b/spec/impl/data_system/streaming_headers_spec.rb
@@ -12,16 +12,7 @@ module DataSystem
       RSpec.describe "StreamingDataSource FDv1 fallback header detection" do
         let(:logger) { double("Logger", info: nil, warn: nil, error: nil, debug: nil) }
         let(:sdk_key) { "test-sdk-key" }
-        let(:config) do
-          double(
-            "Config",
-            logger: logger,
-            stream_uri: "https://stream.example.com",
-            socket_factory: nil,
-            initial_reconnect_delay: 1,
-            instance_id: nil
-          )
-        end
+        let(:config) { LaunchDarkly::Config.new(logger: logger, stream_uri: "https://stream.example.com") }
 
         let(:synchronizer) { LaunchDarkly::DataSystem::StreamingDataSourceBuilder.new.build(sdk_key, config) }
 
diff --git a/spec/impl/data_system/streaming_synchronizer_spec.rb b/spec/impl/data_system/streaming_synchronizer_spec.rb
index 9eed6157..40f71be4 100644
--- a/spec/impl/data_system/streaming_synchronizer_spec.rb
+++ b/spec/impl/data_system/streaming_synchronizer_spec.rb
@@ -12,16 +12,7 @@ module DataSystem
       RSpec.describe StreamingDataSource do
         let(:logger) { double("Logger", info: nil, warn: nil, error: nil, debug: nil) }
         let(:sdk_key) { "test-sdk-key" }
-        let(:config) do
-          double(
-            "Config",
-            logger: logger,
-            stream_uri: "https://stream.example.com",
-            socket_factory: nil,
-            initial_reconnect_delay: 1,
-            instance_id: nil
-          )
-        end
+        let(:config) { LaunchDarkly::Config.new(logger: logger, stream_uri: "https://stream.example.com") }
 
         # Mock SSE event
         class MockSSEEvent