diff --git a/ai/compat_1.1.nut b/ai/compat_1.1.nut
new file mode 100644
--- /dev/null
+++ b/ai/compat_1.1.nut
@@ -0,0 +1,70 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+AILog.Info("1.1 API compatibility in effect.");
+
+AICompany.GetCompanyValue <- function(company)
+{
+	return AICompany.GetQuarterlyCompanyValue(company, AICompany.CURRENT_QUARTER);
+}
+
+AITown.GetLastMonthTransported <- AITown.GetLastMonthSupplied;
+
+AIEvent.AI_ET_INVALID <- AIEvent.ET_INVALID;
+AIEvent.AI_ET_TEST <- AIEvent.ET_TEST;
+AIEvent.AI_ET_SUBSIDY_OFFER <- AIEvent.ET_SUBSIDY_OFFER;
+AIEvent.AI_ET_SUBSIDY_OFFER_EXPIRED <- AIEvent.ET_SUBSIDY_OFFER_EXPIRED;
+AIEvent.AI_ET_SUBSIDY_AWARDED <- AIEvent.ET_SUBSIDY_AWARDED;
+AIEvent.AI_ET_SUBSIDY_EXPIRED <- AIEvent.ET_SUBSIDY_EXPIRED;
+AIEvent.AI_ET_ENGINE_PREVIEW <- AIEvent.ET_ENGINE_PREVIEW;
+AIEvent.AI_ET_COMPANY_NEW <- AIEvent.ET_COMPANY_NEW;
+AIEvent.AI_ET_COMPANY_IN_TROUBLE <- AIEvent.ET_COMPANY_IN_TROUBLE;
+AIEvent.AI_ET_COMPANY_ASK_MERGER <- AIEvent.ET_COMPANY_ASK_MERGER;
+AIEvent.AI_ET_COMPANY_MERGER <- AIEvent.ET_COMPANY_MERGER;
+AIEvent.AI_ET_COMPANY_BANKRUPT <- AIEvent.ET_COMPANY_BANKRUPT;
+AIEvent.AI_ET_VEHICLE_CRASHED <- AIEvent.ET_VEHICLE_CRASHED;
+AIEvent.AI_ET_VEHICLE_LOST <- AIEvent.ET_VEHICLE_LOST;
+AIEvent.AI_ET_VEHICLE_WAITING_IN_DEPOT <- AIEvent.ET_VEHICLE_WAITING_IN_DEPOT;
+AIEvent.AI_ET_VEHICLE_UNPROFITABLE <- AIEvent.ET_VEHICLE_UNPROFITABLE;
+AIEvent.AI_ET_INDUSTRY_OPEN <- AIEvent.ET_INDUSTRY_OPEN;
+AIEvent.AI_ET_INDUSTRY_CLOSE <- AIEvent.ET_INDUSTRY_CLOSE;
+AIEvent.AI_ET_ENGINE_AVAILABLE <- AIEvent.ET_ENGINE_AVAILABLE;
+AIEvent.AI_ET_STATION_FIRST_VEHICLE <- AIEvent.ET_STATION_FIRST_VEHICLE;
+AIEvent.AI_ET_DISASTER_ZEPPELINER_CRASHED <- AIEvent.ET_DISASTER_ZEPPELINER_CRASHED;
+AIEvent.AI_ET_DISASTER_ZEPPELINER_CLEARED <- AIEvent.ET_DISASTER_ZEPPELINER_CLEARED;
+AIEvent.AI_ET_TOWN_FOUNDED <- AIEvent.ET_TOWN_FOUNDED;
+AIOrder.AIOF_NONE <- AIOrder.OF_NONE
+AIOrder.AIOF_NON_STOP_INTERMEDIATE <- AIOrder.OF_NON_STOP_INTERMEDIATE
+AIOrder.AIOF_NON_STOP_DESTINATION <- AIOrder.OF_NON_STOP_DESTINATION
+AIOrder.AIOF_UNLOAD <- AIOrder.OF_UNLOAD
+AIOrder.AIOF_TRANSFER <- AIOrder.OF_TRANSFER
+AIOrder.AIOF_NO_UNLOAD <- AIOrder.OF_NO_UNLOAD
+AIOrder.AIOF_FULL_LOAD <- AIOrder.OF_FULL_LOAD
+AIOrder.AIOF_FULL_LOAD_ANY <- AIOrder.OF_FULL_LOAD_ANY
+AIOrder.AIOF_NO_LOAD <- AIOrder.OF_NO_LOAD
+AIOrder.AIOF_SERVICE_IF_NEEDED <- AIOrder.OF_SERVICE_IF_NEEDED
+AIOrder.AIOF_STOP_IN_DEPOT <- AIOrder.OF_STOP_IN_DEPOT
+AIOrder.AIOF_GOTO_NEAREST_DEPOT <- AIOrder.OF_GOTO_NEAREST_DEPOT
+AIOrder.AIOF_NON_STOP_FLAGS <- AIOrder.OF_NON_STOP_FLAGS
+AIOrder.AIOF_UNLOAD_FLAGS <- AIOrder.OF_UNLOAD_FLAGS
+AIOrder.AIOF_LOAD_FLAGS <- AIOrder.OF_LOAD_FLAGS
+AIOrder.AIOF_DEPOT_FLAGS <- AIOrder.OF_DEPOT_FLAGS
+AIOrder.AIOF_INVALID <- AIOrder.OF_INVALID
+
+/* 1.9 adds a vehicle type parameter. */
+AIBridge._GetName <- AIBridge.GetName;
+AIBridge.GetName <- function(bridge_id)
+{
+	return AIBridge._GetName(bridge_id, AIVehicle.VT_RAIL);
+}
+
+/* 1.9 adds parent_group_id to CreateGroup function */
+AIGroup._CreateGroup <- AIGroup.CreateGroup;
+AIGroup.CreateGroup <- function(vehicle_type)
+{
+	return AIGroup._CreateGroup(vehicle_type, AIGroup.GROUP_INVALID);
+}