diff --git a/src/commands/config/flowConfig.ml b/src/commands/config/flowConfig.ml
index d339573c90d..0d6709b1bc5 100644
--- a/src/commands/config/flowConfig.ml
+++ b/src/commands/config/flowConfig.ml
@@ -391,7 +391,11 @@ module Opts = struct
 
   let autocomplete_mode_parser =
     enum
-      [("typed_ast", Options.Ac_typed_ast); ("on_demand", Options.Ac_on_demand_typing)]
+      [
+        ("typed_ast", Options.Ac_typed_ast);
+        ("on_demand", Options.Ac_on_demand_typing);
+        ("both", Options.Ac_both);
+      ]
       (fun opts v -> Ok { opts with autocomplete_mode = Some v })
 
   let casting_syntax_parser =
diff --git a/src/common/options.ml b/src/common/options.ml
index 2311a198546..c86d2f4366c 100644
--- a/src/common/options.ml
+++ b/src/common/options.ml
@@ -38,6 +38,7 @@ type react_rules =
 type autocomplete_mode =
   | Ac_typed_ast
   | Ac_on_demand_typing
+  | Ac_both (* for comparison purposes *)
 
 type format = {
   opt_bracket_spacing: bool;
diff --git a/src/server/command_handler/commandHandler.ml b/src/server/command_handler/commandHandler.ml
index 97a6553712d..f78f84e5d47 100644
--- a/src/server/command_handler/commandHandler.ml
+++ b/src/server/command_handler/commandHandler.ml
@@ -380,10 +380,15 @@ let autocomplete
         in
         autocomplete_get_results cx (Typed_ast_utils.ALoc_ast aloc_ast)
       in
-      let (token_opt, ac_loc, ac_type_string, results_res) =
+      let ((token_opt, ac_loc, ac_type_string, results_res), initial_json_props) =
         match Options.autocomplete_mode options with
-        | Options.Ac_typed_ast -> autocomplete_fully_type_and_get_results ()
-        | Options.Ac_on_demand_typing -> autocomplete_on_demand_get_results ()
+        | Options.Ac_typed_ast -> (autocomplete_fully_type_and_get_results (), initial_json_props)
+        | Options.Ac_on_demand_typing -> (autocomplete_on_demand_get_results (), initial_json_props)
+        | Options.Ac_both ->
+          let (_, _, _, r1) = autocomplete_on_demand_get_results () in
+          let ((_, _, _, r2) as result) = autocomplete_fully_type_and_get_results () in
+          let equal = AutocompleteService_js.equal_autocomplete_service_result r1 r2 in
+          (result, ("on_demand_compliance", Hh_json.JSON_Bool equal) :: initial_json_props)
       in
       (* Make sure hooks are unset *after* we've gotten the results to account for
        * on-demand type checking. *)