diff --git a/docs/guide/exe_verilator.rst b/docs/guide/exe_verilator.rst
index 938152af8..684d5646d 100644
--- a/docs/guide/exe_verilator.rst
+++ b/docs/guide/exe_verilator.rst
@@ -590,6 +590,8 @@ Summary:
 
 .. option:: -fno-const-bit-op-tree
 
+.. option:: -fno-const-eager
+
 .. option:: -fno-dedup
 
 .. option:: -fno-dfg
diff --git a/src/V3Expand.cpp b/src/V3Expand.cpp
index a0109d51e..952eb2d40 100644
--- a/src/V3Expand.cpp
+++ b/src/V3Expand.cpp
@@ -357,6 +357,16 @@ class ExpandVisitor final : public VNVisitor {
     }
 
     // VISITORS
+    void visit(AstCFunc* nodep) override {
+        iterateChildren(nodep);
+
+        // Constant fold here, as Ast size can likely be reduced
+        if (v3Global.opt.fConstEager()) {
+            AstNode* const editedp = V3Const::constifyEditCpp(nodep);
+            UASSERT_OBJ(editedp == nodep, editedp, "Should not have replaced CFunc");
+        }
+    }
+
     void visit(AstExtend* nodep) override {
         if (nodep->user1SetOnce()) return;  // Process once
         iterateChildren(nodep);
diff --git a/src/V3Options.cpp b/src/V3Options.cpp
index 86a7c0c16..257b1c7fe 100644
--- a/src/V3Options.cpp
+++ b/src/V3Options.cpp
@@ -1320,6 +1320,7 @@ void V3Options::parseOptsList(FileLine* fl, const string& optdir, int argc,
     DECL_OPTION("-fconst", FOnOff, &m_fConst);
     DECL_OPTION("-fconst-before-dfg", FOnOff, &m_fConstBeforeDfg);
     DECL_OPTION("-fconst-bit-op-tree", FOnOff, &m_fConstBitOpTree);
+    DECL_OPTION("-fconst-eager", FOnOff, &m_fConstEager);
     DECL_OPTION("-fdead-assigns", FOnOff, &m_fDeadAssigns);
     DECL_OPTION("-fdead-cells", FOnOff, &m_fDeadCells);
     DECL_OPTION("-fdedup", FOnOff, &m_fDedupe);
diff --git a/src/V3Options.h b/src/V3Options.h
index 6c7fb6acd..8d5a2de1d 100644
--- a/src/V3Options.h
+++ b/src/V3Options.h
@@ -389,6 +389,7 @@ private:
     bool m_fConst;       // main switch: -fno-const: constant folding
     bool m_fConstBeforeDfg = true;  // main switch: -fno-const-before-dfg for testing only!
     bool m_fConstBitOpTree;  // main switch: -fno-const-bit-op-tree constant bit op tree
+    bool m_fConstEager = true;  // main switch: -fno-const-eagerly run V3Const during passes
     bool m_fDedupe;      // main switch: -fno-dedupe: logic deduplication
     bool m_fDfgPeephole = true; // main switch: -fno-dfg-peephole
     bool m_fDfgPreInline;    // main switch: -fno-dfg-pre-inline and -fno-dfg
@@ -701,6 +702,7 @@ public:
     bool fConst() const { return m_fConst; }
     bool fConstBeforeDfg() const { return m_fConstBeforeDfg; }
     bool fConstBitOpTree() const { return m_fConstBitOpTree; }
+    bool fConstEager() const { return m_fConstEager; }
     bool fDedupe() const { return m_fDedupe; }
     bool fDfgPeephole() const { return m_fDfgPeephole; }
     bool fDfgPreInline() const { return m_fDfgPreInline; }
diff --git a/src/V3Subst.cpp b/src/V3Subst.cpp
index 19fd3d9d8..98ceea886 100644
--- a/src/V3Subst.cpp
+++ b/src/V3Subst.cpp
@@ -26,6 +26,7 @@
 
 #include "V3Subst.h"
 
+#include "V3Const.h"
 #include "V3Stats.h"
 
 #include <algorithm>
@@ -361,6 +362,12 @@ class SubstVisitor final : public VNVisitor {
         iterateChildren(nodep);
         for (SubstVarEntry& ip : m_entries) ip.deleteUnusedAssign();
         m_entries.clear();
+
+        // Constant fold here, as Ast size can likely be reduced
+        if (v3Global.opt.fConstEager()) {
+            AstNode* const editedp = V3Const::constifyEditCpp(nodep);
+            UASSERT_OBJ(editedp == nodep, editedp, "Should not have replaced CFunc");
+        }
     }
 
     void visit(AstNode* nodep) override {
diff --git a/test_regress/t/t_case_66bits_no_const_eager.py b/test_regress/t/t_case_66bits_no_const_eager.py
new file mode 100755
index 000000000..2ce516e24
--- /dev/null
+++ b/test_regress/t/t_case_66bits_no_const_eager.py
@@ -0,0 +1,19 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2025 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('vlt')
+test.top_filename = "t/t_case_66bits.v"
+
+test.compile(verilator_flags2=['-fno-const-eager'])
+
+test.execute()
+
+test.passes()