diff --git a/.github/actions/check/action.yml b/.github/actions/check/action.yml
index a1290210..7f6539df 100644
--- a/.github/actions/check/action.yml
+++ b/.github/actions/check/action.yml
@@ -51,4 +51,4 @@ runs:
         test_service_port: 9000
         enable_persistence_tests: true
         token: ${{ inputs.token }}
-        version: v3.0.0-alpha.3
\ No newline at end of file
+        version: v3.0.0-alpha.4
diff --git a/contract-tests/client_entity.rb b/contract-tests/client_entity.rb
index 1b6570f9..0add362f 100644
--- a/contract-tests/client_entity.rb
+++ b/contract-tests/client_entity.rb
@@ -3,6 +3,7 @@
 require 'net/http'
 require 'launchdarkly-server-sdk'
 require './big_segment_store_fixture'
+require './flag_change_listener'
 require './hook'
 require 'http'
 
@@ -117,6 +118,8 @@ def initialize(log, config)
       config[:credential],
       LaunchDarkly::Config.new(opts),
       startWaitTimeMs / 1_000.0)
+
+    @listeners = ListenerRegistry.new(@client.flag_tracker)
   end
 
   def initialized?
@@ -225,7 +228,26 @@ def log
     @log
   end
 
+  def register_flag_change_listener(params)
+    @listeners.register_flag_change_listener(params[:listenerId], params[:callbackUri])
+  end
+
+  def register_flag_value_change_listener(params)
+    context = LaunchDarkly::LDContext.create(params[:context])
+    @listeners.register_flag_value_change_listener(
+      params[:listenerId],
+      params[:flagKey],
+      context,
+      params[:callbackUri]
+    )
+  end
+
+  def unregister_listener(params)
+    @listeners.unregister(params[:listenerId])
+  end
+
   def close
+    @listeners.close_all
     @client.close
     @log.info("Test ended")
   end
diff --git a/contract-tests/flag_change_listener.rb b/contract-tests/flag_change_listener.rb
new file mode 100644
index 00000000..ca87812b
--- /dev/null
+++ b/contract-tests/flag_change_listener.rb
@@ -0,0 +1,127 @@
+require 'http'
+require 'json'
+
+#
+# A listener that receives FlagChange events and POSTs notifications to a callback URI.
+# Implements the #update method expected by the SDK's FlagTracker.
+#
+class FlagChangeCallbackListener
+  def initialize(listener_id, callback_uri)
+    @listener_id = listener_id
+    @callback_uri = callback_uri
+  end
+
+  # @param flag_change [LaunchDarkly::Interfaces::FlagChange]
+  def update(flag_change)
+    payload = {
+      listenerId: @listener_id,
+      flagKey: flag_change.key,
+    }
+    HTTP.post(@callback_uri, json: payload)
+  rescue => e
+    # Log but don't re-raise; listener errors shouldn't crash the test service
+    $log.error("FlagChangeCallbackListener POST failed: #{e}")
+  end
+end
+
+#
+# A listener that receives FlagValueChange events and POSTs notifications to a callback URI.
+# Implements the #update method expected by the SDK's FlagTracker (via FlagValueChangeAdapter).
+#
+class FlagValueChangeCallbackListener
+  def initialize(listener_id, callback_uri)
+    @listener_id = listener_id
+    @callback_uri = callback_uri
+  end
+
+  # @param flag_value_change [LaunchDarkly::Interfaces::FlagValueChange]
+  def update(flag_value_change)
+    payload = {
+      listenerId: @listener_id,
+      flagKey: flag_value_change.key,
+      oldValue: flag_value_change.old_value,
+      newValue: flag_value_change.new_value,
+    }
+    HTTP.post(@callback_uri, json: payload)
+  rescue => e
+    $log.error("FlagValueChangeCallbackListener POST failed: #{e}")
+  end
+end
+
+#
+# Manages all active flag change listener registrations for a single SDK client entity.
+# Thread-safe via a Mutex.
+#
+class ListenerRegistry
+  # @param tracker [LaunchDarkly::Interfaces::FlagTracker]
+  def initialize(tracker)
+    @tracker = tracker
+    @mu = Mutex.new
+    @listeners = {} # listenerId => listener object to pass to remove_listener
+  end
+
+  # Registers a general flag change listener that fires on any flag configuration change.
+  #
+  # @param listener_id [String]
+  # @param callback_uri [String]
+  def register_flag_change_listener(listener_id, callback_uri)
+    listener = FlagChangeCallbackListener.new(listener_id, callback_uri)
+    @tracker.add_listener(listener)
+    store_listener(listener_id, listener)
+  end
+
+  # Registers a flag value change listener that fires when the evaluated value of a
+  # specific flag changes for a given context.
+  #
+  # @param listener_id [String]
+  # @param flag_key [String]
+  # @param context [LaunchDarkly::LDContext]
+  # @param callback_uri [String]
+  def register_flag_value_change_listener(listener_id, flag_key, context, callback_uri)
+    inner_listener = FlagValueChangeCallbackListener.new(listener_id, callback_uri)
+    # add_flag_value_change_listener returns the adapter object that must be passed to
+    # remove_listener for unregistration.
+    adapter = @tracker.add_flag_value_change_listener(flag_key, context, inner_listener)
+    store_listener(listener_id, adapter)
+  end
+
+  # Unregisters a previously registered listener by its ID.
+  #
+  # @param listener_id [String]
+  # @return [Boolean] true if the listener was found and removed
+  def unregister(listener_id)
+    listener = nil
+    @mu.synchronize do
+      listener = @listeners.delete(listener_id)
+    end
+
+    return false if listener.nil?
+
+    @tracker.remove_listener(listener)
+    true
+  end
+
+  # Removes all registered listeners. Called when the SDK client entity shuts down.
+  def close_all
+    listeners_to_remove = nil
+    @mu.synchronize do
+      listeners_to_remove = @listeners.values
+      @listeners = {}
+    end
+
+    listeners_to_remove.each do |listener|
+      @tracker.remove_listener(listener)
+    end
+  end
+
+  # Stores a listener, cancelling any previously registered listener with the same ID.
+  private def store_listener(listener_id, listener)
+    old_listener = nil
+    @mu.synchronize do
+      old_listener = @listeners[listener_id]
+      @listeners[listener_id] = listener
+    end
+
+    @tracker.remove_listener(old_listener) if old_listener
+  end
+end
diff --git a/contract-tests/service.rb b/contract-tests/service.rb
index 1d6383c7..4d083696 100644
--- a/contract-tests/service.rb
+++ b/contract-tests/service.rb
@@ -51,6 +51,8 @@
       'persistent-data-store-consul',
       'persistent-data-store-dynamodb',
       'persistent-data-store-redis',
+      'flag-change-listeners',
+      'flag-value-change-listeners',
     ],
   }.to_json
 end
@@ -128,6 +130,15 @@
   when "contextComparison"
     response = {:equals => client.context_comparison(params[:contextComparison])}
     return [200, nil, response.to_json]
+  when "registerFlagChangeListener"
+    client.register_flag_change_listener(params[:registerFlagChangeListener])
+    return 201
+  when "registerFlagValueChangeListener"
+    client.register_flag_value_change_listener(params[:registerFlagValueChangeListener])
+    return 201
+  when "unregisterListener"
+    success = client.unregister_listener(params[:unregisterListener])
+    return success ? 201 : [400, nil, {:error => "no listener with that id"}.to_json]
   end
 
   return [400, nil, {:error => "Unknown command requested"}.to_json]