@@ -1398,6 +1398,7 @@ let make_options
 |> min Sys_utils.nbr_procs;
 opt_suppress_types = FlowConfig.suppress_types flowconfig;
 opt_max_literal_length = FlowConfig.max_literal_length flowconfig;
+opt_const_type_params = FlowConfig.enable_const_type_params flowconfig;
 opt_component_syntax = FlowConfig.component_syntax flowconfig;
 opt_react_rules = FlowConfig.react_rules flowconfig;
 opt_hook_compatibility = FlowConfig.hook_compatibility flowconfig;

@@ -56,6 +56,7 @@ module Opts = struct
 component_syntax: bool;
 dev_only_refinement_info_as_errors: bool;
 emoji: bool option;
+enable_const_type_params: bool;
 enable_const_params: bool option;
 enums: bool;
 estimate_recheck_time: bool option;
@@ -196,6 +197,7 @@ module Opts = struct
 component_syntax = false;
 dev_only_refinement_info_as_errors = false;
 emoji = None;
+enable_const_type_params = false;
 enable_const_params = None;
 enums = false;
 estimate_recheck_time = None;
@@ -1028,6 +1030,9 @@ module Opts = struct
 ( "dev_only.refinement_info_as_errors",
 boolean (fun opts v -> Ok { opts with dev_only_refinement_info_as_errors = v })
 );
+( "experimental.const_type_params",
+boolean (fun opts v -> Ok { opts with enable_const_type_params = v })
+);
 ("emoji", boolean (fun opts v -> Ok { opts with emoji = Some v }));
 ("enums", boolean (fun opts v -> Ok { opts with enums = v }));
 ("estimate_recheck_time", estimate_recheck_time_parser);
@@ -1830,6 +1835,8 @@ let dev_only_refinement_info_as_errors c = c.options.Opts.dev_only_refinement_in
 
 let emoji c = c.options.Opts.emoji
 
+let enable_const_type_params c = c.options.Opts.enable_const_type_params
+
 let enable_const_params c = c.options.Opts.enable_const_params
 
 let enums c = c.options.Opts.enums

@@ -90,6 +90,8 @@ val dev_only_refinement_info_as_errors : config -> bool
 
 val emoji : config -> bool option
 
+val enable_const_type_params : config -> bool
+
 val enable_const_params : config -> bool option
 
 val enums : config -> bool

@@ -88,6 +88,7 @@ type t = {
 opt_casting_syntax: CastingSyntax.t;
 opt_channel_mode: [ `pipe | `socket ];
 opt_component_syntax: bool;
+opt_const_type_params: bool;
 opt_hook_compatibility_includes: Str.regexp list;
 opt_hook_compatibility_excludes: Str.regexp list;
 opt_hook_compatibility: bool;
@@ -198,6 +199,8 @@ let channel_mode opts = opts.opt_channel_mode
 
 let component_syntax opts = opts.opt_component_syntax
 
+let const_type_params opts = opts.opt_const_type_params
+
 let hook_compatibility opts = opts.opt_hook_compatibility
 
 let hook_compatibility_includes opts = opts.opt_hook_compatibility_includes

@@ -113,6 +113,7 @@ let stub_metadata ~root ~checked =
 [ValidateRefAccessDuringRender; DeepReadOnlyProps; DeepReadOnlyHookReturns; RulesOfHooks];
 react_rules_always = false;
 dev_only_refinement_info_as_errors = false;
+enable_const_type_params = false;
 enable_const_params = false;
 enable_enums = true;
 enable_jest_integration = false;

@@ -39,6 +39,7 @@ let stub_metadata ~root ~checked =
 react_rules = [];
 react_rules_always = false;
 dev_only_refinement_info_as_errors = false;
+enable_const_type_params = false;
 enable_const_params = false;
 enable_enums = true;
 enable_jest_integration = false;

@@ -34,6 +34,7 @@ let metadata =
 react_rules = [];
 react_rules_always = false;
 dev_only_refinement_info_as_errors = false;
+enable_const_type_params = false;
 enable_const_params = false;
 enable_enums = true;
 enable_jest_integration = false;

@@ -32,6 +32,7 @@ let metadata =
 react_rules = [];
 react_rules_always = false;
 dev_only_refinement_info_as_errors = false;
+enable_const_type_params = false;
 enable_const_params = false;
 enable_enums = true;
 enable_jest_integration = false;

@@ -43,6 +43,7 @@ type metadata = {
 react_rules: Options.react_rules list;
 react_rules_always: bool;
 dev_only_refinement_info_as_errors: bool;
+enable_const_type_params: bool;
 enable_const_params: bool;
 enable_enums: bool;
 enable_jest_integration: bool;
@@ -286,6 +287,7 @@ let metadata_of_options options =
 react_rules = Options.react_rules options;
 react_rules_always = false;
 dev_only_refinement_info_as_errors = Options.dev_only_refinement_info_as_errors options;
+enable_const_type_params = Options.const_type_params options;
 enable_const_params = Options.enable_const_params options;
 enable_enums = Options.enums options;
 enable_jest_integration = Options.enable_jest_integration options;
@@ -538,6 +540,8 @@ let react_rule_enabled cx rule = List.mem rule cx.metadata.react_rules
 
 let dev_only_refinement_info_as_errors cx = cx.metadata.dev_only_refinement_info_as_errors
 
+let enable_const_type_params cx = cx.metadata.enable_const_type_params
+
 let enable_const_params cx =
 cx.metadata.enable_const_params || cx.metadata.strict || cx.metadata.strict_local
 

@@ -93,6 +93,7 @@ type metadata = {
 react_rules: Options.react_rules list;
 react_rules_always: bool;
 dev_only_refinement_info_as_errors: bool;
+enable_const_type_params: bool;
 enable_const_params: bool;
 enable_enums: bool;
 enable_jest_integration: bool;
@@ -200,6 +201,8 @@ val react_rules_always : t -> bool
 
 val dev_only_refinement_info_as_errors : t -> bool
 
+val enable_const_type_params : t -> bool
+
 val enable_const_params : t -> bool
 
 val enable_enums : t -> bool

@@ -2562,12 +2562,14 @@ module Make (Statement : Statement_sig.S) : Type_annotation_sig.S = struct
 in
 let reason = mk_annot_reason (RType (OrdinaryName name)) name_loc in
 let polarity = polarity cx variance in
-Base.Option.iter const ~f:(fun (loc, _) ->
-Flow_js_utils.add_output
-env.cx
-(Error_message.EUnsupportedSyntax (loc, Flow_intermediate_error_types.ConstTypeParameter)
-)
-);
+if not (Context.enable_const_type_params cx) then
+Base.Option.iter const ~f:(fun (loc, _) ->
+Flow_js_utils.add_output
+env.cx
+(Error_message.EUnsupportedSyntax
+(loc, Flow_intermediate_error_types.ConstTypeParameter)
+)
+);
 (match bound_kind with
 | Ast.Type.TypeParam.Extends when not (kind = Flow_ast_mapper.InferTP || Context.ts_syntax cx)
 ->