diff --git a/analysis/reanalyze/src/dead_optional_args.ml b/analysis/reanalyze/src/dead_optional_args.ml
index 4866f75077..c3b84a28a4 100644
--- a/analysis/reanalyze/src/dead_optional_args.ml
+++ b/analysis/reanalyze/src/dead_optional_args.ml
@@ -16,11 +16,8 @@ let rec has_optional_args (texpr : Types.type_expr) =
   | _ -> false
 
 let add_function_reference ~config ~cross_file ~(loc_from : Location.t)
-    ~(loc_to : Location.t) ~type_from ~type_to =
-  (* Keep this filter type-based rather than consulting the declaration table.
-     References can be collected before their target declaration is visited,
-     notably in [let rec ... and ...] groups. *)
-  if has_optional_args type_from && has_optional_args type_to then (
+    ~(loc_to : Location.t) =
+  if active () then (
     let pos_to = loc_to.loc_start in
     let pos_from = loc_from.loc_start in
     if config.Dce_config.cli.debug then
diff --git a/analysis/reanalyze/src/dead_value.ml b/analysis/reanalyze/src/dead_value.ml
index 0dd3205160..d44ceac649 100644
--- a/analysis/reanalyze/src/dead_value.ml
+++ b/analysis/reanalyze/src/dead_value.ml
@@ -593,20 +593,21 @@ let traverse_structure ~config ~decls ~refs ~cross_file ~file ~do_types
 
 (* Merge a location's references to another one's *)
 let process_value_dependency ~config ~refs ~cross_file
-    ( ({
-         val_loc = {loc_start = pos_to; loc_ghost = ghost1} as loc_to;
-         val_type = type_to;
-       } :
-        Types.value_description),
-      ({
-         val_loc = {loc_start = pos_from; loc_ghost = ghost2} as loc_from;
-         val_type = type_from;
-       } :
-        Types.value_description) ) =
+    ({
+       value_loc = {loc_start = pos_to; loc_ghost = ghost1} as loc_to;
+       spec_loc = {loc_start = pos_from; loc_ghost = ghost2} as loc_from;
+       optional_args;
+     } :
+      Cmt_format.value_dependency) =
   if (not ghost1) && (not ghost2) && pos_to <> pos_from then (
     add_value_reference ~config ~refs ~binding:Location.none ~loc_from ~loc_to;
-    Dead_optional_args.add_function_reference ~config ~cross_file ~loc_from
-      ~loc_to ~type_from ~type_to)
+    (* The compiler decides this from the two types rather than reanalyze
+       consulting its declaration table: references can be collected before
+       their target declaration is visited, notably in [let rec ... and ...]
+       groups. *)
+    if optional_args then
+      Dead_optional_args.add_function_reference ~config ~cross_file ~loc_from
+        ~loc_to)
 
 let process_structure ~config ~decls ~refs ~cross_file ~file
     ~cmt_value_dependencies ~do_types ~do_externals
diff --git a/changes/smaller-cmt-files.internal.md b/changes/smaller-cmt-files.internal.md
new file mode 100644
index 0000000000..de1da7715f
--- /dev/null
+++ b/changes/smaller-cmt-files.internal.md
@@ -0,0 +1 @@
+- Write smaller `.cmt` files by dropping data no tool reads: full value descriptions in the value dependencies, the command line and environment summaries.
diff --git a/compiler/bsc/rescript_compiler_driver.ml b/compiler/bsc/rescript_compiler_driver.ml
index 06f3461f88..9a5f16088a 100644
--- a/compiler/bsc/rescript_compiler_driver.ml
+++ b/compiler/bsc/rescript_compiler_driver.ml
@@ -592,7 +592,6 @@ let with_fresh_request_states ~cwd action =
 let run_argv ?run_external ~capture ~cwd argv =
   with_fresh_request_states ~cwd (fun () ->
       start_request ();
-      Cmt_format.set_args argv;
       let execute () =
         try
           Bsc_args.parse_exn ~argv (command_line_flags ()) anonymous ~usage;
diff --git a/compiler/ext/compiler_request_state.ml b/compiler/ext/compiler_request_state.ml
index db71341576..6ac9922b28 100644
--- a/compiler/ext/compiler_request_state.ml
+++ b/compiler/ext/compiler_request_state.ml
@@ -3,7 +3,6 @@ type t = {
   cwd: string;
   mutable input_name: string;
   mutable command_runner: string -> int;
-  mutable cmt_args: string array;
   mutable lambda_raise_count: int;
   mutable lambda_negative_raise_count: int;
   mutable builtin_ppx_local_module_counter: int;
@@ -22,7 +21,6 @@ let create ~active cwd =
     cwd;
     input_name = "_none_";
     command_runner = Sys.command;
-    cmt_args = Sys.argv;
     lambda_raise_count = 0;
     lambda_negative_raise_count = 0;
     builtin_ppx_local_module_counter = 0;
diff --git a/compiler/ext/compiler_request_state.mli b/compiler/ext/compiler_request_state.mli
index 71e3bed64f..7bb74ef4b0 100644
--- a/compiler/ext/compiler_request_state.mli
+++ b/compiler/ext/compiler_request_state.mli
@@ -3,7 +3,6 @@ type t = {
   cwd: string;
   mutable input_name: string;
   mutable command_runner: string -> int;
-  mutable cmt_args: string array;
   mutable lambda_raise_count: int;
   mutable lambda_negative_raise_count: int;
   mutable builtin_ppx_local_module_counter: int;
diff --git a/compiler/jsoo/jsoo_playground_main.ml b/compiler/jsoo/jsoo_playground_main.ml
index dd8484a49b..77aed6e3aa 100644
--- a/compiler/jsoo/jsoo_playground_main.ml
+++ b/compiler/jsoo/jsoo_playground_main.ml
@@ -493,7 +493,6 @@ module Compile = struct
         Cmt_format.cmt_modname = modulename;
         cmt_annots;
         cmt_value_dependencies = [];
-        cmt_args = [||];
         cmt_source_digest = None;
         cmt_extra_info = {Cmt_utils.deprecated_used = []};
       }
diff --git a/compiler/ml/cmt_format.ml b/compiler/ml/cmt_format.ml
index cc2484a453..d86f88a8a0 100644
--- a/compiler/ml/cmt_format.ml
+++ b/compiler/ml/cmt_format.ml
@@ -1,7 +1,5 @@
 include Cmt_format_common
 
-let set_args = Cmt_format_persistence.set_args
-
 let save_cmt filename modname binary_annots sourcefile =
   Cmt_format_persistence.save_cmt filename modname binary_annots sourcefile;
   clear ()
diff --git a/compiler/ml/cmt_format.mli b/compiler/ml/cmt_format.mli
index 8bdd9642c3..843d711c5d 100644
--- a/compiler/ml/cmt_format.mli
+++ b/compiler/ml/cmt_format.mli
@@ -38,13 +38,22 @@ and binary_part =
   | Partial_signature_item of signature_item
   | Partial_module_type of module_type
 
+type value_dependency = {
+  value_loc: Location.t;  (** The value that was matched. *)
+  spec_loc: Location.t;  (** The declaration it was matched against. *)
+  optional_args: bool;
+      (** Both types are functions with an optional parameter. *)
+}
+(** One value inclusion check (an implementation against its interface, or a
+    module against a module type), recorded for reanalyze. *)
+
 type cmt_infos = {
   cmt_modname: string;
   cmt_annots: binary_annots;
-  cmt_value_dependencies:
-    (Types.value_description * Types.value_description) list;
-  cmt_args: string array;
+  cmt_value_dependencies: value_dependency list;
   cmt_source_digest: Digest.t option;
+      (** Digest of the source file, which [rescript-tools migrate] compares
+          to tell whether the .cmt is current. *)
   cmt_extra_info: Cmt_utils.cmt_extra_info;
 }
 
@@ -52,10 +61,6 @@ type error = Not_a_typedtree of string
 
 exception Error of error
 
-val set_args : string array -> unit
-(** Set the logical compiler arguments recorded in subsequently written CMT
-    files. Long-lived compiler hosts set this at each request boundary. *)
-
 val read_cmt : string -> cmt_infos
 val read_cmi : string -> Cmi_format.cmi_infos
 
diff --git a/compiler/ml/cmt_format_common.ml b/compiler/ml/cmt_format_common.ml
index fdb6140216..61023d0ed9 100644
--- a/compiler/ml/cmt_format_common.ml
+++ b/compiler/ml/cmt_format_common.ml
@@ -35,36 +35,31 @@ and binary_part =
   | Partial_signature_item of signature_item
   | Partial_module_type of module_type
 
+(* What reanalyze needs from one value inclusion check. Keeping the two full
+   value descriptions instead made up a fifth of the stdlib's .cmt bytes. *)
+type value_dependency = {
+  value_loc: Location.t;
+  spec_loc: Location.t;
+  optional_args: bool;
+}
+
 type cmt_infos = {
   cmt_modname: string;
   cmt_annots: binary_annots;
-  cmt_value_dependencies:
-    (Types.value_description * Types.value_description) list;
-  cmt_args: string array;
+  cmt_value_dependencies: value_dependency list;
   cmt_source_digest: Digest.t option;
   cmt_extra_info: Cmt_utils.cmt_extra_info;
 }
 
-(* Note that in Typerex, there is an awful hack to save a cmt file
-   together with the interface file that was generated by ocaml (this
-   is because the installed version of ocaml might differ from the one
-   integrated in Typerex).
-*)
-
 type error = Not_a_typedtree of string
 
-let need_to_clear_env =
-  try
-    ignore (Sys.getenv "OCAML_BINANNOT_WITHENV");
-    false
-  with Not_found -> true
-
-let keep_only_summary = Env.keep_only_summary
-
 open Tast_mapper
 
 let cenv =
-  {Tast_mapper.default with env = (fun _sub env -> keep_only_summary env)}
+  {
+    Tast_mapper.default with
+    env = (fun _sub env -> Env.keep_only_local_constraints env);
+  }
 
 let clear_part = function
   | Partial_structure s -> Partial_structure (cenv.structure cenv s)
@@ -78,14 +73,12 @@ let clear_part = function
   | Partial_module_type s -> Partial_module_type (cenv.module_type cenv s)
 
 let clear_env binary_annots =
-  if need_to_clear_env then
-    match binary_annots with
-    | Implementation s -> Implementation (cenv.structure cenv s)
-    | Interface s -> Interface (cenv.signature cenv s)
-    | Partial_implementation array ->
-      Partial_implementation (Array.map clear_part array)
-    | Partial_interface array -> Partial_interface (Array.map clear_part array)
-  else binary_annots
+  match binary_annots with
+  | Implementation s -> Implementation (cenv.structure cenv s)
+  | Interface s -> Interface (cenv.signature cenv s)
+  | Partial_implementation array ->
+    Partial_implementation (Array.map clear_part array)
+  | Partial_interface array -> Partial_interface (Array.map clear_part array)
 
 exception Error of error
 
@@ -138,7 +131,6 @@ let accumulators =
       {saved_types = []; value_deps = []; deprecated_used = []})
 
 let current_accumulators () = Domain.DLS.get accumulators
-let value_dependencies () = (current_accumulators ()).value_deps
 let deprecated_uses () = (current_accumulators ()).deprecated_used
 
 let clear () =
@@ -170,7 +162,35 @@ let[@live] record_deprecated_used ?deprecated_context ?migration_template
 
 let _ = Cmt_utils.record_deprecated_used := record_deprecated_used
 
-let record_value_dependency vd1 vd2 =
-  if vd1.Types.val_loc <> vd2.Types.val_loc then
+(* Whether a type is a function with an optional parameter. *)
+let rec takes_optional_args (t : Types.type_expr) =
+  match t.desc with
+  | Tarrow (params, _) ->
+    List.exists
+      (fun ({lbl} : Types.arg) ->
+        match lbl with
+        | Optional _ -> true
+        | Nolabel | Labelled _ -> false)
+      params
+  | Tlink t | Tsubst t -> takes_optional_args t
+  | _ -> false
+
+let record_value_dependency (vd1 : Types.value_description)
+    (vd2 : Types.value_description) =
+  if vd1.val_loc <> vd2.val_loc then
     let state = current_accumulators () in
     state.value_deps <- (vd1, vd2) :: state.value_deps
+
+(* The flag is decided when the .cmt is written, not when the dependency is
+   recorded: the inclusion check that follows the recording can still
+   instantiate weak type variables of the value. *)
+let value_dependencies () =
+  List.map
+    (fun ((vd1 : Types.value_description), (vd2 : Types.value_description)) ->
+      {
+        value_loc = vd1.val_loc;
+        spec_loc = vd2.val_loc;
+        optional_args =
+          takes_optional_args vd1.val_type && takes_optional_args vd2.val_type;
+      })
+    (current_accumulators ()).value_deps
diff --git a/compiler/ml/env.ml b/compiler/ml/env.ml
index fee35abf0a..0659044773 100644
--- a/compiler/ml/env.ml
+++ b/compiler/ml/env.ml
@@ -147,17 +147,6 @@ end
 
 module Path_map = Map.Make (Path)
 
-type summary =
-  | Env_empty
-  | Env_value of summary * Ident.t * value_description
-  | Env_type of summary * Ident.t * type_declaration
-  | Env_extension of summary * Ident.t * extension_constructor
-  | Env_module of summary * Ident.t * module_declaration
-  | Env_modtype of summary * Ident.t * modtype_declaration
-  | Env_open of summary * Path.t
-  | Env_functor_arg of summary * Ident.t
-  | Env_copy_types of summary * string list
-
 module Tycomp_tbl = struct
   (** This module is used to store components of types (i.e. labels
         and constructors).  We keep a representation of each nested
@@ -375,7 +364,6 @@ type t = {
   modtypes: modtype_declaration Id_tbl.t;
   components: module_components Id_tbl.t;
   functor_args: unit Ident.tbl;
-  summary: summary;
   local_constraints: type_declaration Path_map.t;
   gadt_instances: (int * Type_set.t ref) list;
   flags: int;
@@ -455,7 +443,6 @@ let empty =
     modules = Id_tbl.empty;
     modtypes = Id_tbl.empty;
     components = Id_tbl.empty;
-    summary = Env_empty;
     local_constraints = Path_map.empty;
     gadt_instances = [];
     flags = 0;
@@ -1088,7 +1075,7 @@ let copy_types l env =
   let values =
     List.fold_left (fun env s -> Id_tbl.update s f env) env.values l
   in
-  {env with values; summary = Env_copy_types (env.summary, l)}
+  {env with values}
 
 let mark_value_used env name vd =
   if not (is_implicit_coercion env) then
@@ -1551,11 +1538,7 @@ and check_value_name name loc =
 and store_value ?check id decl env =
   check_value_name (Ident.name id) decl.val_loc;
   may (fun f -> check_usage decl.val_loc id f (value_declarations ())) check;
-  {
-    env with
-    values = Id_tbl.add id decl env.values;
-    summary = Env_value (env.summary, id, decl);
-  }
+  {env with values = Id_tbl.add id decl env.values}
 
 and store_type ~check id info env =
   let loc = info.type_loc in
@@ -1598,7 +1581,6 @@ and store_type ~check id info env =
         (fun (id, descr) labels -> Tycomp_tbl.add id descr labels)
         labels env.labels;
     types = Id_tbl.add id (info, descrs) env.types;
-    summary = Env_type (env.summary, id, info);
   }
 
 and store_type_infos id info env =
@@ -1607,11 +1589,7 @@ and store_type_infos id info env =
      manifest-ness of the type.  Used in components_of_module to
      keep track of type abbreviations (e.g. type t = float) in the
      computation of label representations. *)
-  {
-    env with
-    types = Id_tbl.add id (info, ([], [])) env.types;
-    summary = Env_type (env.summary, id, info);
-  }
+  {env with types = Id_tbl.add id (info, ([], [])) env.types}
 
 and store_extension ~check id ext env =
   let loc = ext.ext_loc in
@@ -1635,7 +1613,6 @@ and store_extension ~check id ext env =
     env with
     constrs =
       Tycomp_tbl.add id (Datarepr.extension_descr (Pident id) ext) env.constrs;
-    summary = Env_extension (env.summary, id, ext);
   }
 
 and store_module ~check id md env =
@@ -1654,15 +1631,10 @@ and store_module ~check id md env =
         (components_of_module ~deprecated ~loc:md.md_loc env Subst.identity
            (Pident id) md.md_type)
         env.components;
-    summary = Env_module (env.summary, id, md);
   }
 
 and store_modtype id info env =
-  {
-    env with
-    modtypes = Id_tbl.add id info env.modtypes;
-    summary = Env_modtype (env.summary, id, info);
-  }
+  {env with modtypes = Id_tbl.add id info env.modtypes}
 
 (* Compute the components of a functor application in a path. *)
 
@@ -1689,11 +1661,7 @@ let _ =
 (* Insertion of bindings by identifier *)
 
 let add_functor_arg id env =
-  {
-    env with
-    functor_args = Ident.add id () env.functor_args;
-    summary = Env_functor_arg (env.summary, id);
-  }
+  {env with functor_args = Ident.add id () env.functor_args}
 
 let add_value ?check id desc env = store_value ?check id desc env
 
@@ -1780,17 +1748,7 @@ let add_components slot root env0 comps =
 
   let modules = add (fun x -> `Module x) comps.comp_modules env0.modules in
 
-  {
-    env0 with
-    summary = Env_open (env0.summary, root);
-    constrs;
-    labels;
-    values;
-    types;
-    modtypes;
-    components;
-    modules;
-  }
+  {env0 with constrs; labels; values; types; modtypes; components; modules}
 
 let open_signature slot root env0 =
   match get_components (find_module_descr root env0) with
@@ -2002,16 +1960,11 @@ let last_env () = Domain.DLS.get last_env_key
 let last_reduced_env_key = Request_local.new_key (fun () -> ref empty)
 let last_reduced_env () = Domain.DLS.get last_reduced_env_key
 
-let keep_only_summary env =
+let keep_only_local_constraints env =
   if !(last_env ()) == env then !(last_reduced_env ())
   else
     let new_env =
-      {
-        empty with
-        summary = env.summary;
-        local_constraints = env.local_constraints;
-        flags = env.flags;
-      }
+      {empty with local_constraints = env.local_constraints; flags = env.flags}
     in
     last_env () := env;
     last_reduced_env () := new_env;
diff --git a/compiler/ml/env.mli b/compiler/ml/env.mli
index a7b680ac53..a2ebfcaf66 100644
--- a/compiler/ml/env.mli
+++ b/compiler/ml/env.mli
@@ -20,17 +20,6 @@ open Types
 module Path_map :
   Map.S with type key = Path.t and type 'a t = 'a Map.Make(Path).t
 
-type summary =
-  | Env_empty
-  | Env_value of summary * Ident.t * value_description
-  | Env_type of summary * Ident.t * type_declaration
-  | Env_extension of summary * Ident.t * extension_constructor
-  | Env_module of summary * Ident.t * module_declaration
-  | Env_modtype of summary * Ident.t * modtype_declaration
-  | Env_open of summary * Path.t
-  | Env_functor_arg of summary * Ident.t
-  | Env_copy_types of summary * string list
-
 type t
 
 val empty : t
@@ -200,13 +189,11 @@ val imports : unit -> (string * Digest.t option) list
 val crc_units : unit -> Consistbl.t
 val add_import : string -> unit
 
-(* Summaries -- compact representation of an environment, to be
-   exported in debugging information. *)
-
-(* Return an equivalent environment where all fields have been reset,
-   except the summary. *)
+val keep_only_local_constraints : t -> t
+(** The environment stored in .cmt files: empty except for its GADT local
+    constraints and flags. Tools only look things up in it, and the lookups
+    find nothing in an empty table. *)
 
-val keep_only_summary : t -> t
 type error =
   | Illegal_renaming of string * string * string
   | Inconsistent_import of string * string * string
diff --git a/compiler/ml/platform/native/cmt_format_persistence.ml b/compiler/ml/platform/native/cmt_format_persistence.ml
index 461230a126..f911cf044e 100644
--- a/compiler/ml/platform/native/cmt_format_persistence.ml
+++ b/compiler/ml/platform/native/cmt_format_persistence.ml
@@ -15,8 +15,6 @@
 
 open Cmt_format_common
 
-let set_args value = (Compiler_request_state.current ()).cmt_args <- value
-
 let read_source_file path =
   let path = Compiler_request_state.resolve_path path in
   match Build_file_store.read path with
@@ -32,7 +30,6 @@ let save_cmt filename modname binary_annots sourcefile =
         cmt_modname = modname;
         cmt_annots = clear_env binary_annots;
         cmt_value_dependencies = value_dependencies ();
-        cmt_args = (Compiler_request_state.current ()).cmt_args;
         cmt_source_digest =
           Misc.may_map
             (fun path -> Digest.string (read_source_file path))
diff --git a/compiler/ml/platform/playground/cmt_format_persistence.ml b/compiler/ml/platform/playground/cmt_format_persistence.ml
index 48dccc6d62..713f8376e7 100644
--- a/compiler/ml/platform/playground/cmt_format_persistence.ml
+++ b/compiler/ml/platform/playground/cmt_format_persistence.ml
@@ -1,3 +1 @@
-let set_args _value = ()
-
 let save_cmt _filename _modname _binary_annots _sourcefile = ()
diff --git a/tests/ounit_tests/ounit_compiler_request_tests.ml b/tests/ounit_tests/ounit_compiler_request_tests.ml
index 24b121ef3c..38278613ad 100644
--- a/tests/ounit_tests/ounit_compiler_request_tests.ml
+++ b/tests/ounit_tests/ounit_compiler_request_tests.ml
@@ -813,26 +813,22 @@ let cmt_accumulator_isolation_tests _context =
   let left =
     Domain.spawn (fun () ->
         Cmt_format.clear ();
-        Cmt_format.set_args [|"bsc"; "First.res"|];
         Cmt_format.add_saved_type saved_part;
         Atomic.set left_ready true;
         wait_for_atomic right_ready;
-        ( List.length (Cmt_format.get_saved_types ()),
-          (Compiler_request_state.current ()).cmt_args ))
+        List.length (Cmt_format.get_saved_types ()))
   in
   let right =
     Domain.spawn (fun () ->
         wait_for_atomic left_ready;
         Cmt_format.clear ();
-        Cmt_format.set_args [|"bsc"; "Second.res"|];
         Cmt_format.add_saved_type saved_part;
         Cmt_format.add_saved_type saved_part;
         Atomic.set right_ready true;
-        ( List.length (Cmt_format.get_saved_types ()),
-          (Compiler_request_state.current ()).cmt_args ))
+        List.length (Cmt_format.get_saved_types ()))
   in
-  assert_equal (1, [|"bsc"; "First.res"|]) (Domain.join left);
-  assert_equal (2, [|"bsc"; "Second.res"|]) (Domain.join right)
+  assert_equal 1 (Domain.join left);
+  assert_equal 2 (Domain.join right)
 
 let package_output_isolation_tests _context =
   let left_ready = Atomic.make false in
@@ -1304,17 +1300,13 @@ let state_boundary_tests _context =
         (contains_text after_source_flags.stderr "Warning number 39")
         "source-level compiler flags are reset between requests";
       write root "Mapped.res" "let mapped = 1\n";
-      let mapped_args, mapped =
+      let _, mapped =
         run root ~extra:["-bs-source-map"; "linked"] "Mapped.res"
       in
       expect_code 0 mapped;
       check
         (Sys.file_exists (Filename.concat root "Mapped.js.map"))
         "the requested source map is generated";
-      let cmt = Cmt_format.read_cmt (Filename.concat root "Mapped.cmt") in
-      check
-        (Array.to_list cmt.cmt_args = ("bsc" :: mapped_args) @ ["Mapped.res"])
-        "CMT metadata records the logical request argv";
       write root "Plain.res" "let plain = 1\n";
       let _, plain =
         run root