diff --git a/CHANGELOG.md b/CHANGELOG.md
index 01f20d52d4..53a065db80 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,7 @@
 #### :rocket: New Feature
 
 - Introduced a new `%ffi` extension that provides a more robust mechanism for JavaScript function interoperation by considering function arity in type constraints. This enhancement improves safety when dealing with JavaScript functions by enforcing type constraints based on the arity of the function. [PR #6251](https://github.com/rescript-lang/rescript-compiler/pull/6251)
+- Extended untagged variants with function types https://github.com/rescript-lang/rescript-compiler/pull/6279
 
 #### :bug: Bug Fix
 
diff --git a/jscomp/core/js_exp_make.ml b/jscomp/core/js_exp_make.ml
index 2499bcf5a4..2d6b3e122b 100644
--- a/jscomp/core/js_exp_make.ml
+++ b/jscomp/core/js_exp_make.ml
@@ -769,6 +769,7 @@ let tag_type = function
   | Undefined -> undefined
   | Untagged IntType -> str "number"
   | Untagged FloatType -> str "number"
+  | Untagged FunctionType -> str "function"
   | Untagged StringType -> str "string"
   | Untagged ArrayType -> str "Array" ~delim:DNoQuotes
   | Untagged ObjectType -> str "object"
diff --git a/jscomp/frontend/ast_core_type.ml b/jscomp/frontend/ast_core_type.ml
index acba47587b..6379c14f30 100644
--- a/jscomp/frontend/ast_core_type.ml
+++ b/jscomp/frontend/ast_core_type.ml
@@ -125,7 +125,7 @@ let get_uncurry_arity (ty : t) =
   | _ -> None
 
 let get_curry_arity (ty : t) =
-  if Ast_uncurried.typeIsUncurriedFun ty then
+  if Ast_uncurried.coreTypeIsUncurriedFun ty then
     let arity, _ = Ast_uncurried.typeExtractUncurriedFun ty in
     arity
   else get_uncurry_arity_aux ty 0
diff --git a/jscomp/frontend/ast_external_process.ml b/jscomp/frontend/ast_external_process.ml
index a1f8afed38..2267526bbb 100644
--- a/jscomp/frontend/ast_external_process.ml
+++ b/jscomp/frontend/ast_external_process.ml
@@ -68,7 +68,7 @@ let spec_of_ptyp (nolabel : bool) (ptyp : Parsetree.core_type) :
     | _ -> Bs_syntaxerr.err ptyp.ptyp_loc Invalid_bs_unwrap_type)
   | `Uncurry opt_arity -> (
     let real_arity =
-      if Ast_uncurried.typeIsUncurriedFun ptyp then
+      if Ast_uncurried.coreTypeIsUncurriedFun ptyp then
         let arity, _ = Ast_uncurried.typeExtractUncurriedFun ptyp in
         Some arity
       else Ast_core_type.get_uncurry_arity ptyp
diff --git a/jscomp/gentype/EmitType.ml b/jscomp/gentype/EmitType.ml
index 7f6dbe7e27..8b60601e2b 100644
--- a/jscomp/gentype/EmitType.ml
+++ b/jscomp/gentype/EmitType.ml
@@ -184,7 +184,14 @@ let rec renderType ~(config : Config.t) ?(indent = None) ~typeNameIsInterface
                |> field ~name:(Runtime.jsVariantTag ~polymorphic:false)
              in
              match (unboxed, type_) with
-             | true, type_ -> type_ |> render
+             | true, type_ ->
+               let needParens =
+                 match type_ with
+                 | Function _ -> true
+                 | _ -> false
+               in
+               let t = type_ |> render in
+               if needParens then EmitText.parens [t] else t
              | false, type_ when polymorphic ->
                (* poly variant *)
                [
diff --git a/jscomp/gentype_tests/typescript-react-example/bsconfig.json b/jscomp/gentype_tests/typescript-react-example/bsconfig.json
index 99dd46c6f2..fcb209e06a 100644
--- a/jscomp/gentype_tests/typescript-react-example/bsconfig.json
+++ b/jscomp/gentype_tests/typescript-react-example/bsconfig.json
@@ -24,6 +24,7 @@
       "subdirs": true
     }
   ],
+  "uncurried": false,
   "package-specs": {
     "module": "es6",
     "in-source": true
diff --git a/jscomp/gentype_tests/typescript-react-example/package-lock.json b/jscomp/gentype_tests/typescript-react-example/package-lock.json
index ba9633e710..03ddaf278c 100644
--- a/jscomp/gentype_tests/typescript-react-example/package-lock.json
+++ b/jscomp/gentype_tests/typescript-react-example/package-lock.json
@@ -21,7 +21,7 @@
     },
     "../../..": {
       "name": "rescript",
-      "version": "11.0.0-alpha.5",
+      "version": "11.0.0-beta.2",
       "dev": true,
       "hasInstallScript": true,
       "license": "SEE LICENSE IN LICENSE",
@@ -35,6 +35,9 @@
         "nyc": "^15.0.0",
         "prettier": "^2.7.1",
         "rollup": "^0.49.2"
+      },
+      "engines": {
+        "node": ">=10"
       }
     },
     "node_modules/@rescript/react": {
diff --git a/jscomp/gentype_tests/typescript-react-example/src/Unboxed.gen.tsx b/jscomp/gentype_tests/typescript-react-example/src/Unboxed.gen.tsx
index 2df57b84fa..e1a45ac733 100644
--- a/jscomp/gentype_tests/typescript-react-example/src/Unboxed.gen.tsx
+++ b/jscomp/gentype_tests/typescript-react-example/src/Unboxed.gen.tsx
@@ -18,6 +18,9 @@ export type r1 = number;
 // tslint:disable-next-line:interface-over-type-literal
 export type r2 = string;
 
+// tslint:disable-next-line:interface-over-type-literal
+export type t = number[] | number | ((_1:number) => number);
+
 export const testV1: (x:v1) => v1 = UnboxedBS.testV1;
 
 export const r2Test: (x:r2) => r2 = UnboxedBS.r2Test;
diff --git a/jscomp/gentype_tests/typescript-react-example/src/Unboxed.res b/jscomp/gentype_tests/typescript-react-example/src/Unboxed.res
index 75ec318742..851ebc4349 100644
--- a/jscomp/gentype_tests/typescript-react-example/src/Unboxed.res
+++ b/jscomp/gentype_tests/typescript-react-example/src/Unboxed.res
@@ -13,3 +13,6 @@ type r1 = {x: int}
 type r2 = B({g: string})
 
 @genType let r2Test = (x: r2) => x
+
+@genType @unboxed
+type t = Array(array<int>) | Record({x:int}) | Function((. int) => int)
diff --git a/jscomp/ml/ast_uncurried.ml b/jscomp/ml/ast_uncurried.ml
index 09341a709a..8b418ef287 100644
--- a/jscomp/ml/ast_uncurried.ml
+++ b/jscomp/ml/ast_uncurried.ml
@@ -63,12 +63,19 @@ let exprExtractUncurriedFun (expr : Parsetree.expression) =
   | Pexp_construct ({ txt = Lident "Function$" }, Some e) -> e
   | _ -> assert false
 
-let typeIsUncurriedFun (typ : Parsetree.core_type) =
+let coreTypeIsUncurriedFun (typ : Parsetree.core_type) =
   match typ.ptyp_desc with
   | Ptyp_constr ({txt = Lident "function$"}, [{ptyp_desc = Ptyp_arrow _}; _]) ->
     true
   | _ -> false
 
+let typeIsUncurriedFun (typ : Types.type_expr) =
+  match typ.desc with
+  | Tconstr (Pident {name = "function$"}, [{desc = Tarrow _}; _], _) ->
+    true
+  | _ -> false
+
+
 let typeExtractUncurriedFun (typ : Parsetree.core_type) =
   match typ.ptyp_desc with
   | Ptyp_constr ({txt = Lident "function$"}, [tArg; tArity]) ->
diff --git a/jscomp/ml/ast_untagged_variants.ml b/jscomp/ml/ast_untagged_variants.ml
index ce5e01bf73..b6d472be99 100644
--- a/jscomp/ml/ast_untagged_variants.ml
+++ b/jscomp/ml/ast_untagged_variants.ml
@@ -1,4 +1,4 @@
-type untaggedError = OnlyOneUnknown | AtMostOneObject | AtMostOneArray | AtMostOneString | AtMostOneNumber | DuplicateLiteral of string
+type untaggedError = OnlyOneUnknown | AtMostOneObject | AtMostOneArray | AtMostOneFunction | AtMostOneString | AtMostOneNumber | DuplicateLiteral of string
 type error =
   | InvalidVariantAsAnnotation
   | Duplicated_bs_as
@@ -22,6 +22,7 @@ let report_error ppf =
     | OnlyOneUnknown -> "An unknown case must be the only case with payloads."
     | AtMostOneObject -> "At most one case can be an object type."
     | AtMostOneArray -> "At most one case can be an array type."
+    | AtMostOneFunction -> "At most one case can be a function type."
     | AtMostOneString -> "At most one case can be a string type."
     | AtMostOneNumber -> "At most one case can be a number type (int or float)."
     | DuplicateLiteral s -> "Duplicate literal " ^ s ^ "."
@@ -29,7 +30,7 @@ let report_error ppf =
 
 (* Type of the runtime representation of an untagged block (case with payoad) *)
 type block_type =
-  | IntType | StringType | FloatType | ArrayType | ObjectType | UnknownType
+  | IntType | StringType | FloatType | ArrayType | FunctionType | ObjectType | UnknownType
 
 (*
   Type of the runtime representation of a tag.
@@ -116,6 +117,10 @@ let get_block_type ~env (cstr: Types.constructor_declaration) : block_type optio
       Some FloatType
   | true, Cstr_tuple [{desc = Tconstr (path, _, _)}] when Path.same path Predef.path_array ->
       Some ArrayType
+  | true, Cstr_tuple [{desc = Tconstr _}  as t] when Ast_uncurried.typeIsUncurriedFun t ->
+      Some FunctionType
+  | true, Cstr_tuple [{desc = Tarrow _} ] ->
+      Some FunctionType
   | true, Cstr_tuple [{desc = Tconstr (path, _, _)}] when Path. same path Predef.path_string ->
       Some StringType
   | true, Cstr_tuple [{desc = Tconstr _} as t] when type_is_builtin_object t ->
@@ -162,6 +167,7 @@ let checkInvariant ~isUntaggedDef ~(consts : (Location.t * tag) list) ~(blocks :
   let string_literals = ref StringSet.empty in
   let nonstring_literals = ref StringSet.empty in
   let arrayTypes = ref 0 in
+  let functionTypes = ref 0 in
   let objectTypes = ref 0 in
   let stringTypes = ref 0 in
   let numberTypes = ref 0 in
@@ -181,6 +187,8 @@ let checkInvariant ~isUntaggedDef ~(consts : (Location.t * tag) list) ~(blocks :
       then raise (Error (loc, InvalidUntaggedVariantDefinition AtMostOneObject));
     if !arrayTypes > 1
       then raise (Error (loc, InvalidUntaggedVariantDefinition AtMostOneArray));
+    if !functionTypes > 1
+      then raise (Error (loc, InvalidUntaggedVariantDefinition AtMostOneFunction));
     if !stringTypes > 1
       then raise (Error (loc, InvalidUntaggedVariantDefinition AtMostOneString));
     if !numberTypes > 1
@@ -214,6 +222,9 @@ let checkInvariant ~isUntaggedDef ~(consts : (Location.t * tag) list) ~(blocks :
     | Some ArrayType ->
       incr arrayTypes;
       invariant loc
+    | Some FunctionType ->
+      incr functionTypes;
+      invariant loc
     | Some (IntType | FloatType) ->
       incr numberTypes;
       invariant loc
@@ -266,6 +277,8 @@ module DynamicChecks = struct
   let nil = Null |> tag_type
   let undefined = Undefined |> tag_type
   let object_ = Untagged ObjectType |> tag_type
+
+  let function_ = Untagged FunctionType |> tag_type
   let string = Untagged StringType |> tag_type
   let number = Untagged IntType |> tag_type
 
@@ -298,6 +311,8 @@ module DynamicChecks = struct
       typeof e != number
     | ArrayType -> 
       not (is_array e)
+    | FunctionType ->
+      typeof e != function_
     | ObjectType when literals_overlaps_with_object () = false ->
       typeof e != object_
     | ObjectType (* overlap *) ->
@@ -341,9 +356,8 @@ module DynamicChecks = struct
   let add_runtime_type_check ~tag_type ~(block_cases: block_type list) x y =
     let has_array() = Ext_list.exists block_cases (fun t -> t = ArrayType) in
     match tag_type with
-    | Untagged IntType
-    | Untagged StringType
-    | Untagged FloatType -> typeof y == x
+    | Untagged (IntType | StringType | FloatType | FunctionType) ->
+      typeof y == x
     | Untagged ObjectType ->
       if has_array() then
         typeof y == x &&& not (is_array y)
diff --git a/jscomp/syntax/src/react_jsx_common.ml b/jscomp/syntax/src/react_jsx_common.ml
index ae4a529d6b..0cfe798a78 100644
--- a/jscomp/syntax/src/react_jsx_common.ml
+++ b/jscomp/syntax/src/react_jsx_common.ml
@@ -45,7 +45,7 @@ let raiseErrorMultipleReactComponent ~loc =
 let optionalAttr = ({txt = "res.optional"; loc = Location.none}, PStr [])
 
 let extractUncurried typ =
-  if Ast_uncurried.typeIsUncurriedFun typ then
+  if Ast_uncurried.coreTypeIsUncurriedFun typ then
     let _arity, t = Ast_uncurried.typeExtractUncurriedFun typ in
     t
   else typ
diff --git a/jscomp/syntax/src/res_parens.ml b/jscomp/syntax/src/res_parens.ml
index 13e801b5c0..5fc2ab9ff8 100644
--- a/jscomp/syntax/src/res_parens.ml
+++ b/jscomp/syntax/src/res_parens.ml
@@ -442,7 +442,7 @@ let includeModExpr modExpr =
 let arrowReturnTypExpr typExpr =
   match typExpr.Parsetree.ptyp_desc with
   | Parsetree.Ptyp_arrow _ -> true
-  | _ when Ast_uncurried.typeIsUncurriedFun typExpr -> true
+  | _ when Ast_uncurried.coreTypeIsUncurriedFun typExpr -> true
   | _ -> false
 
 let patternRecordRowRhs (pattern : Parsetree.pattern) =
diff --git a/jscomp/syntax/src/res_printer.ml b/jscomp/syntax/src/res_printer.ml
index bf714208f5..36a98f4ed4 100644
--- a/jscomp/syntax/src/res_printer.ml
+++ b/jscomp/syntax/src/res_printer.ml
@@ -1591,7 +1591,7 @@ and printTypExpr ~(state : State.t) (typExpr : Parsetree.core_type) cmtTbl =
         let doc = printTypExpr ~state n cmtTbl in
         match n.ptyp_desc with
         | Ptyp_arrow _ | Ptyp_tuple _ | Ptyp_alias _ -> addParens doc
-        | _ when Ast_uncurried.typeIsUncurriedFun n -> addParens doc
+        | _ when Ast_uncurried.coreTypeIsUncurriedFun n -> addParens doc
         | _ -> doc
       in
       Doc.group
@@ -1652,7 +1652,7 @@ and printTypExpr ~(state : State.t) (typExpr : Parsetree.core_type) cmtTbl =
         let needsParens =
           match typ.ptyp_desc with
           | Ptyp_arrow _ -> true
-          | _ when Ast_uncurried.typeIsUncurriedFun typ -> true
+          | _ when Ast_uncurried.coreTypeIsUncurriedFun typ -> true
           | _ -> false
         in
         let doc = printTypExpr ~state typ cmtTbl in
@@ -1664,7 +1664,7 @@ and printTypExpr ~(state : State.t) (typExpr : Parsetree.core_type) cmtTbl =
     | Ptyp_object (fields, openFlag) ->
       printObject ~state ~inline:false fields openFlag cmtTbl
     | Ptyp_arrow _ -> printArrow ~uncurried:false typExpr
-    | Ptyp_constr _ when Ast_uncurried.typeIsUncurriedFun typExpr ->
+    | Ptyp_constr _ when Ast_uncurried.coreTypeIsUncurriedFun typExpr ->
       let arity, tArg = Ast_uncurried.typeExtractUncurriedFun typExpr in
       printArrow ~uncurried:true ~arity tArg
     | Ptyp_constr (longidentLoc, [{ptyp_desc = Ptyp_object (fields, openFlag)}])
diff --git a/jscomp/test/UntaggedVariants.js b/jscomp/test/UntaggedVariants.js
index f7b023abe7..5b63c99774 100644
--- a/jscomp/test/UntaggedVariants.js
+++ b/jscomp/test/UntaggedVariants.js
@@ -362,6 +362,28 @@ var OptionUnboxingHeuristic = {
   untaggedInlineMultinaryOption: untaggedInlineMultinaryOption
 };
 
+function classify$9(v) {
+  if (Array.isArray(v)) {
+    return Caml_array.get(v, 0);
+  }
+  switch (typeof v) {
+    case "object" :
+        return v.x;
+    case "function" :
+        return v(3);
+    
+  }
+}
+
+var ff = (function (x) {
+    return x + 1 | 0;
+  });
+
+var TestFunctionCase = {
+  classify: classify$9,
+  ff: ff
+};
+
 var i = 42;
 
 var i2 = 42.5;
@@ -402,4 +424,5 @@ exports.OverlapObject = OverlapObject;
 exports.RecordIsObject = RecordIsObject;
 exports.ArrayAndObject = ArrayAndObject;
 exports.OptionUnboxingHeuristic = OptionUnboxingHeuristic;
+exports.TestFunctionCase = TestFunctionCase;
 /* l2 Not a pure module */
diff --git a/jscomp/test/UntaggedVariants.res b/jscomp/test/UntaggedVariants.res
index 0355ee671e..460f1357f6 100644
--- a/jscomp/test/UntaggedVariants.res
+++ b/jscomp/test/UntaggedVariants.res
@@ -293,3 +293,17 @@ module OptionUnboxingHeuristic = {
   type untaggedInlineMultinaryOption = A | B({x: option<int>, y?: string})
   let untaggedInlineMultinaryOption = (x: untaggedInlineMultinaryOption) => Some(x)
 }
+
+module TestFunctionCase = {
+  @unboxed
+  type t = Array(array<int>) | Record({x:int}) | Function((. int) => int)
+
+  let classify = v =>
+    switch v {
+    | Record({x}) => x
+    | Array(a) => a[0]
+    | Function(f) => f(. 3) 
+    }
+
+    let ff = Function((. x) => x+1)
+}
\ No newline at end of file