diff --git a/CHANGELOG.md b/CHANGELOG.md
index bc70c3ced5..a3dbabc3dc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,10 @@
 
 # 12.0.0-alpha.10 (Unreleased)
 
+#### :house: Internal
+
+- Clean up legacy tags handling. https://github.com/rescript-lang/rescript/pull/7309
+
 # 12.0.0-alpha.9
 
 #### :boom: Breaking Change
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index bdd07022d6..90d8a60953 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -47,7 +47,10 @@ Make sure you have [opam](https://opam.ocaml.org/doc/Install.html) installed on
 opam init
 
 # Any recent OCaml version works as a development compiler
-opam switch create 5.3.0 # can also create local switch with opam switch create
+# Can also create local switch with opam switch create
+# If you get "No compiler matching `5.3.0' found" error,
+# then you need to run `opam update && opam upgrade` first
+opam switch create 5.3.0
 
 # Install dev dependencies from OPAM
 opam install . --deps-only --with-test --with-dev-setup -y
diff --git a/compiler/core/js_exp_make.ml b/compiler/core/js_exp_make.ml
index 8980667ff2..4879bedf52 100644
--- a/compiler/core/js_exp_make.ml
+++ b/compiler/core/js_exp_make.ml
@@ -338,9 +338,6 @@ let eight_int_literal : t =
 let nine_int_literal : t =
   {expression_desc = Number (Int {i = 9l; c = None}); comment = None}
 
-let obj_int_tag_literal : t =
-  {expression_desc = Number (Int {i = 248l; c = None}); comment = None}
-
 let int ?comment ?c i : t = {expression_desc = Number (Int {i; c}); comment}
 
 let bigint ?comment sign i : t =
@@ -364,7 +361,6 @@ let small_int i : t =
   | 7 -> seven_int_literal
   | 8 -> eight_int_literal
   | 9 -> nine_int_literal
-  | 248 -> obj_int_tag_literal
   | i -> int (Int32.of_int i)
 
 let true_ : t = {comment = None; expression_desc = Bool true}
diff --git a/compiler/core/js_exp_make.mli b/compiler/core/js_exp_make.mli
index 3b9f216274..14865e1769 100644
--- a/compiler/core/js_exp_make.mli
+++ b/compiler/core/js_exp_make.mli
@@ -132,7 +132,6 @@ val zero_int_literal : t
 
 (* val one_int_literal : t *)
 val zero_float_lit : t
-(* val obj_int_tag_literal : t *)
 
 val zero_bigint_literal : t
 
diff --git a/lib/es6/Primitive_hash.js b/lib/es6/Primitive_hash.js
index ed778e6fd9..6807c3b44d 100644
--- a/lib/es6/Primitive_hash.js
+++ b/lib/es6/Primitive_hash.js
@@ -118,15 +118,11 @@ function hash(count, _limit, seed, obj) {
       if (size !== 0) {
         let obj_tag = obj$1.TAG;
         let tag = (size << 10) | obj_tag;
-        if (obj_tag === 248) {
-          s = hash_mix_int(s, obj$1[1]);
-        } else {
-          s = hash_mix_int(s, tag);
-          let v = size - 1 | 0;
-          let block = v < num ? v : num;
-          for (let i = 0; i <= block; ++i) {
-            push_back(queue, obj$1[i]);
-          }
+        s = hash_mix_int(s, tag);
+        let v = size - 1 | 0;
+        let block = v < num ? v : num;
+        for (let i = 0; i <= block; ++i) {
+          push_back(queue, obj$1[i]);
         }
       } else {
         let size$1 = (function(obj,cb){
diff --git a/lib/es6/Primitive_object.js b/lib/es6/Primitive_object.js
index 59d4b80e4b..4dc3663fdd 100644
--- a/lib/es6/Primitive_object.js
+++ b/lib/es6/Primitive_object.js
@@ -1,6 +1,5 @@
 
 
-import * as Primitive_int from "./Primitive_int.js";
 import * as Primitive_bool from "./Primitive_bool.js";
 import * as Primitive_float from "./Primitive_float.js";
 import * as Primitive_string from "./Primitive_string.js";
@@ -107,16 +106,6 @@ function compare(a, b) {
       }
       let tag_a = a.TAG;
       let tag_b = b.TAG;
-      if (tag_a === 248) {
-        return Primitive_int.compare(a[1], b[1]);
-      }
-      if (tag_a === 251) {
-        throw {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "equal: abstract value",
-          Error: new Error()
-        };
-      }
       if (tag_a !== tag_b) {
         if (tag_a < tag_b) {
           return -1;
@@ -247,16 +236,6 @@ function equal(a, b) {
   }
   let tag_a = a.TAG;
   let tag_b = b.TAG;
-  if (tag_a === 248) {
-    return a[1] === b[1];
-  }
-  if (tag_a === 251) {
-    throw {
-      RE_EXN_ID: "Invalid_argument",
-      _1: "equal: abstract value",
-      Error: new Error()
-    };
-  }
   if (tag_a !== tag_b) {
     return false;
   }
diff --git a/lib/js/Primitive_hash.js b/lib/js/Primitive_hash.js
index c54048c4f6..6ae6d31529 100644
--- a/lib/js/Primitive_hash.js
+++ b/lib/js/Primitive_hash.js
@@ -118,15 +118,11 @@ function hash(count, _limit, seed, obj) {
       if (size !== 0) {
         let obj_tag = obj$1.TAG;
         let tag = (size << 10) | obj_tag;
-        if (obj_tag === 248) {
-          s = hash_mix_int(s, obj$1[1]);
-        } else {
-          s = hash_mix_int(s, tag);
-          let v = size - 1 | 0;
-          let block = v < num ? v : num;
-          for (let i = 0; i <= block; ++i) {
-            push_back(queue, obj$1[i]);
-          }
+        s = hash_mix_int(s, tag);
+        let v = size - 1 | 0;
+        let block = v < num ? v : num;
+        for (let i = 0; i <= block; ++i) {
+          push_back(queue, obj$1[i]);
         }
       } else {
         let size$1 = (function(obj,cb){
diff --git a/lib/js/Primitive_object.js b/lib/js/Primitive_object.js
index 598c002036..b747f0665c 100644
--- a/lib/js/Primitive_object.js
+++ b/lib/js/Primitive_object.js
@@ -1,6 +1,5 @@
 'use strict';
 
-let Primitive_int = require("./Primitive_int.js");
 let Primitive_bool = require("./Primitive_bool.js");
 let Primitive_float = require("./Primitive_float.js");
 let Primitive_string = require("./Primitive_string.js");
@@ -107,16 +106,6 @@ function compare(a, b) {
       }
       let tag_a = a.TAG;
       let tag_b = b.TAG;
-      if (tag_a === 248) {
-        return Primitive_int.compare(a[1], b[1]);
-      }
-      if (tag_a === 251) {
-        throw {
-          RE_EXN_ID: "Invalid_argument",
-          _1: "equal: abstract value",
-          Error: new Error()
-        };
-      }
       if (tag_a !== tag_b) {
         if (tag_a < tag_b) {
           return -1;
@@ -247,16 +236,6 @@ function equal(a, b) {
   }
   let tag_a = a.TAG;
   let tag_b = b.TAG;
-  if (tag_a === 248) {
-    return a[1] === b[1];
-  }
-  if (tag_a === 251) {
-    throw {
-      RE_EXN_ID: "Invalid_argument",
-      _1: "equal: abstract value",
-      Error: new Error()
-    };
-  }
   if (tag_a !== tag_b) {
     return false;
   }
diff --git a/runtime/Primitive_hash.res b/runtime/Primitive_hash.res
index e195f2c947..0adc4ade6b 100644
--- a/runtime/Primitive_hash.res
+++ b/runtime/Primitive_hash.res
@@ -174,22 +174,18 @@ let hash = (count: int, _limit, seed: int, obj: Obj.t): int => {
         if size != 0 {
           let obj_tag = Obj.tag(obj)
           let tag = lor(lsl(size, 10), obj_tag)
-          if obj_tag == 248 /* Obj.object_tag */ {
-            s.contents = hash_mix_int(s.contents, (Obj.obj(Obj.getField(obj, 1)): int))
-          } else {
-            s.contents = hash_mix_int(s.contents, tag)
-            let block = {
-              let v = size - 1
-              if v < num.contents {
-                v
-              } else {
-                num.contents
-              }
-            }
-            for i in 0 to block {
-              push_back(queue, Obj.getField(obj, i))
+          s.contents = hash_mix_int(s.contents, tag)
+          let block = {
+            let v = size - 1
+            if v < num.contents {
+              v
+            } else {
+              num.contents
             }
           }
+          for i in 0 to block {
+            push_back(queue, Obj.getField(obj, i))
+          }
         } else {
           let size: int = %raw(`function(obj,cb){
             var size = 0  
diff --git a/runtime/Primitive_object.res b/runtime/Primitive_object.res
index ae655a20d5..62fdfa743b 100644
--- a/runtime/Primitive_object.res
+++ b/runtime/Primitive_object.res
@@ -32,7 +32,6 @@ type t = Primitive_object_extern.t
 let repr = Primitive_object_extern.repr
 let magic = Primitive_object_extern.magic
 let tag = Primitive_object_extern.tag
-let field = Primitive_object_extern.getField
 let size = Primitive_object_extern.size
 
 module O = {
@@ -145,11 +144,7 @@ let rec compare = (a: t, b: t): int =>
       } else {
         let tag_a = tag(a)
         let tag_b = tag(b)
-        if tag_a == 248 /* object/exception */ {
-          Pervasives.compare((magic(field(a, 1)): int), magic(field(b, 1)))
-        } else if tag_a == 251 /* abstract_tag */ {
-          raise(Invalid_argument("equal: abstract value"))
-        } else if tag_a != tag_b {
+        if tag_a != tag_b {
           if tag_a < tag_b {
             -1
           } else {
@@ -277,11 +272,7 @@ let rec equal = (a: t, b: t): bool =>
         /* [a] [b] could not be null, so it can not raise */
         let tag_a = tag(a)
         let tag_b = tag(b)
-        if tag_a == 248 /* object/exception */ {
-          magic(field(a, 1)) === magic(field(b, 1))
-        } else if tag_a == 251 /* abstract_tag */ {
-          raise(Invalid_argument("equal: abstract value"))
-        } else if tag_a != tag_b {
+        if tag_a != tag_b {
           false
         } else {
           let len_a = size(a)