diff --git a/src/Lean/Compiler/LCNF/ExtractClosed.lean b/src/Lean/Compiler/LCNF/ExtractClosed.lean
new file mode 100644
index 0000000000..8c0679f623
--- /dev/null
+++ b/src/Lean/Compiler/LCNF/ExtractClosed.lean
@@ -0,0 +1,156 @@
+/-
+Copyright (c) 2025 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Cameron Zwarich
+-/
+prelude
+import Lean.Compiler.ClosedTermCache
+import Lean.Compiler.NeverExtractAttr
+import Lean.Compiler.LCNF.Basic
+import Lean.Compiler.LCNF.InferType
+import Lean.Compiler.LCNF.Internalize
+import Lean.Compiler.LCNF.MonoTypes
+import Lean.Compiler.LCNF.PassManager
+import Lean.Compiler.LCNF.ToExpr
+
+namespace Lean.Compiler.LCNF
+namespace ExtractClosed
+
+abbrev ExtractM := StateRefT (Array CodeDecl) CompilerM
+
+mutual
+
+partial def extractLetValue (v : LetValue) : ExtractM Unit := do
+  match v with
+  | .const _ _ args => args.forM extractArg
+  | .fvar fnVar args =>
+    extractFVar fnVar
+    args.forM extractArg
+  | .proj _ _ baseVar => extractFVar baseVar
+  | .lit _ | .erased => return ()
+
+partial def extractArg (arg : Arg) : ExtractM Unit := do
+  match arg with
+  | .fvar fvarId => extractFVar fvarId
+  | .type _ | .erased => return ()
+
+partial def extractFVar (fvarId : FVarId) : ExtractM Unit := do
+  if let some letDecl ← findLetDecl? fvarId then
+    modify fun decls => decls.push (.let letDecl)
+    extractLetValue letDecl.value
+
+end
+
+def isIrrelevantArg (arg : Arg) : Bool :=
+  match arg with
+  | .erased | .type _ => true
+  | .fvar _ => false
+
+structure Context where
+  baseName : Name
+  sccDecls : Array Decl
+
+structure State where
+  decls : Array Decl := {}
+
+abbrev M := ReaderT Context $ StateRefT State CompilerM
+
+mutual
+
+partial def shouldExtractLetValue (isRoot : Bool) (v : LetValue) : M Bool := do
+  match v with
+  | .lit (.str _) => return true
+  | .lit (.nat v) =>
+    -- The old compiler's implementation used the runtime's `is_scalar` function, which
+    -- introduces a dependency on the architecture used by the compiler.
+    return v >= Nat.pow 2 63
+  | .lit _ | .erased => return !isRoot
+  | .const name _ args =>
+    if (← read).sccDecls.any (·.name == name) then
+      return false
+    if hasNeverExtractAttribute (← getEnv) name then
+      return false
+    if isRoot then
+      if let some constInfo := (← getEnv).find? name then
+        let shouldExtract := match constInfo with
+        | .defnInfo val => val.type.isForall
+        | .ctorInfo _ => !(args.all isIrrelevantArg)
+        | _ => true
+        if !shouldExtract then
+          return false
+    args.allM shouldExtractArg
+  | .fvar fnVar args => return (← shouldExtractFVar fnVar) && (← args.allM shouldExtractArg)
+  | .proj _ _ baseVar => shouldExtractFVar baseVar
+
+partial def shouldExtractArg (arg : Arg) : M Bool := do
+  match arg with
+  | .fvar fvarId => shouldExtractFVar fvarId
+  | .type _ | .erased => return true
+
+partial def shouldExtractFVar (fvarId : FVarId) : M Bool := do
+  if let some letDecl ← findLetDecl? fvarId then
+    shouldExtractLetValue false letDecl.value
+  else
+    return false
+
+end
+
+mutual
+
+partial def visitCode (code : Code) : M Code := do
+  match code with
+  | .let decl k =>
+    if (← shouldExtractLetValue true decl.value) then
+      let ⟨_, decls⟩ ← extractLetValue decl.value |>.run {}
+      let decls := decls.reverse.push (.let decl)
+      let decls ← decls.mapM Internalize.internalizeCodeDecl |>.run' {}
+      let closedCode := attachCodeDecls decls (.return decls.back!.fvarId)
+      let closedExpr := closedCode.toExpr
+      let env ← getEnv
+      let name ← if let some closedTermName := getClosedTermName? env closedExpr then
+        eraseCode closedCode
+        pure closedTermName
+      else
+        let name := (← read).baseName ++ (`_closedTerm).appendIndexAfter (← get).decls.size
+        cacheClosedTermName env closedExpr name |> setEnv
+        let decl := { name, levelParams := [], type := decl.type, params := #[],
+                      value := .code closedCode, inlineAttr? := some .noinline }
+        decl.saveMono
+        modify fun s => { s with decls := s.decls.push decl }
+        pure name
+      let decl ← decl.updateValue (.const name [] #[])
+      return code.updateLet! decl (← visitCode k)
+    else
+      return code.updateLet! decl (← visitCode k)
+  | .fun decl k =>
+    let decl ← decl.updateValue (← visitCode decl.value)
+    return code.updateFun! decl (← visitCode k)
+  | .jp decl k =>
+    let decl ← decl.updateValue (← visitCode decl.value)
+    return code.updateFun! decl (← visitCode k)
+  | .cases cases =>
+    let alts ← cases.alts.mapM (fun alt => do return alt.updateCode (← visitCode alt.getCode))
+    return code.updateAlts! alts
+  | .jmp .. | .return _ | .unreach .. => return code
+
+end
+
+def visitDecl (decl : Decl) : M Decl := do
+  let value ← decl.value.mapCodeM visitCode
+  return { decl with value }
+
+end ExtractClosed
+
+partial def Decl.extractClosed (decl : Decl) (sccDecls : Array Decl) : CompilerM (Array Decl) := do
+  let ⟨decl, s⟩ ← ExtractClosed.visitDecl decl |>.run { baseName := decl.name, sccDecls } |>.run {}
+  return s.decls.push decl
+
+def extractClosed : Pass where
+  phase := .mono
+  name := `extractClosed
+  run := fun decls =>
+    decls.foldlM (init := #[]) fun newDecls decl => return newDecls ++ (← decl.extractClosed decls)
+
+builtin_initialize registerTraceClass `Compiler.extractClosed (inherited := true)
+
+end Lean.Compiler.LCNF
diff --git a/src/Lean/Compiler/LCNF/Passes.lean b/src/Lean/Compiler/LCNF/Passes.lean
index 2abd1941ac..ac4cd4ae9d 100644
--- a/src/Lean/Compiler/LCNF/Passes.lean
+++ b/src/Lean/Compiler/LCNF/Passes.lean
@@ -19,6 +19,7 @@ import Lean.Compiler.LCNF.FloatLetIn
 import Lean.Compiler.LCNF.ReduceArity
 import Lean.Compiler.LCNF.ElimDeadBranches
 import Lean.Compiler.LCNF.StructProjCases
+import Lean.Compiler.LCNF.ExtractClosed
 
 namespace Lean.Compiler.LCNF