diff --git a/pkgs/applications/editors/jupyter-kernels/xeus-cling/0003-Remove-unsupported-src-root-flag.patch b/pkgs/applications/editors/jupyter-kernels/xeus-cling/0003-Remove-unsupported-src-root-flag.patch
new file mode 100644
index 0000000000000..8a44919e47d59
--- /dev/null
+++ b/pkgs/applications/editors/jupyter-kernels/xeus-cling/0003-Remove-unsupported-src-root-flag.patch
@@ -0,0 +1,85 @@
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index 43718f5..d0d8670 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -63,8 +63,7 @@ if(LLVM_CONFIG)
+         "--bindir"
+         "--libdir"
+         "--includedir"
+-        "--prefix"
+-        "--src-root")
++        "--prefix")
+     execute_process(COMMAND ${CONFIG_COMMAND}
+                     RESULT_VARIABLE HAD_ERROR
+                     OUTPUT_VARIABLE CONFIG_OUTPUT)
+diff --git a/src/xmagics/executable.cpp b/src/xmagics/executable.cpp
+index 391c8c9..aba5e03 100644
+--- a/src/xmagics/executable.cpp
++++ b/src/xmagics/executable.cpp
+@@ -12,6 +12,7 @@
+ #include <iterator>
+ #include <fstream>
+ #include <memory>
++#include <optional>
+ #include <string>
+ #include <vector>
+ 
+@@ -25,7 +26,7 @@
+ #include "clang/AST/ASTContext.h"
+ #include "clang/AST/DeclGroup.h"
+ #include "clang/AST/RecursiveASTVisitor.h"
+-#include "clang/Basic/DebugInfoOptions.h"
++#include "llvm/Frontend/Debug/Options.h"
+ #include "clang/Basic/Sanitizers.h"
+ #include "clang/Basic/TargetInfo.h"
+ #include "clang/CodeGen/BackendUtil.h"
+@@ -115,7 +116,7 @@ namespace xcpp
+             // Filter out functions added by Cling.
+             if (auto Identifier = D->getIdentifier())
+             {
+-                if (Identifier->getName().startswith("__cling"))
++                if (Identifier->getName().starts_with("__cling"))
+                 {
+                     return true;
+                 }
+@@ -153,12 +154,13 @@ namespace xcpp
+         if (EnableDebugInfo)
+         {
+             CodeGenOpts.setDebugInfo(
+-                clang::codegenoptions::DebugInfoKind::FullDebugInfo);
++                llvm::codegenoptions::DebugInfoKind::FullDebugInfo);
+         }
+ 
+         std::unique_ptr<clang::CodeGenerator> CG(clang::CreateLLVMCodeGen(
+-            CI->getDiagnostics(), "object", HeaderSearchOpts,
+-            CI->getPreprocessorOpts(), CodeGenOpts, *Context));
++            CI->getDiagnostics(), "object", 
++            llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>(&CI->getVirtualFileSystem()),
++            HeaderSearchOpts, CI->getPreprocessorOpts(), CodeGenOpts, *Context));
+         CG->Initialize(AST);
+ 
+         FindTopLevelDecls Visitor(CG.get());
+@@ -186,7 +188,9 @@ namespace xcpp
+         EmitBackendOutput(CI->getDiagnostics(), HeaderSearchOpts,
+                           CodeGenOpts, CI->getTargetOpts(),
+                           CI->getLangOpts(), DataLayout, CG->GetModule(),
+-                          clang::Backend_EmitObj, std::move(OS));
++                          clang::Backend_EmitObj, 
++                          llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>(&CI->getVirtualFileSystem()),
++                          std::move(OS));
+         return true;
+     }
+ 
+@@ -222,10 +226,10 @@ namespace xcpp
+ 
+         llvm::StringRef OutputFileStr(OutputFile);
+         llvm::StringRef ErrorFileStr(ErrorFile);
+-        llvm::SmallVector<llvm::Optional<llvm::StringRef>, 16> Redirects = {llvm::NoneType::None, OutputFileStr, ErrorFileStr};
++        llvm::SmallVector<std::optional<llvm::StringRef>, 16> Redirects = {std::nullopt, OutputFileStr, ErrorFileStr};
+ 
+         // Finally run the linker.
+-        int ret = llvm::sys::ExecuteAndWait(Compiler, Args, llvm::NoneType::None,
++        int ret = llvm::sys::ExecuteAndWait(Compiler, Args, std::nullopt,
+                                             Redirects);
+ 
+         // Read back output and error streams.
diff --git a/pkgs/applications/editors/jupyter-kernels/xeus-cling/xeus-cling.nix b/pkgs/applications/editors/jupyter-kernels/xeus-cling/xeus-cling.nix
index af0c5cce88f36..843f4a07b71de 100644
--- a/pkgs/applications/editors/jupyter-kernels/xeus-cling/xeus-cling.nix
+++ b/pkgs/applications/editors/jupyter-kernels/xeus-cling/xeus-cling.nix
@@ -3,7 +3,7 @@
   clangStdenv,
   cmake,
   fetchFromGitHub,
-  llvmPackages_13,
+  llvmPackages_18,
   # Libraries
   argparse,
   cling,
@@ -65,6 +65,7 @@ clangStdenv.mkDerivation rec {
   patches = [
     ./0001-Fix-bug-in-extract_filename.patch
     ./0002-Don-t-pass-extra-includes-configure-this-with-flags.patch
+    ./0003-Remove-unsupported-src-root-flag.patch
   ];
 
   nativeBuildInputs = [ cmake ];
@@ -73,7 +74,7 @@ clangStdenv.mkDerivation rec {
     cling.unwrapped
     cppzmq
     libuuid
-    llvmPackages_13.llvm
+    llvmPackages_18.llvm
     ncurses
     openssl
     pugixml
diff --git a/pkgs/by-name/cl/cling/fix-new-parser.patch b/pkgs/by-name/cl/cling/fix-new-parser.patch
new file mode 100644
index 0000000000000..9869686e6dda7
--- /dev/null
+++ b/pkgs/by-name/cl/cling/fix-new-parser.patch
@@ -0,0 +1,54 @@
+From cd4d1d8c4963620a6a84834948845df81fbbd70b Mon Sep 17 00:00:00 2001
+From: Jonas Hahnfeld <jonas.hahnfeld@cern.ch>
+Date: Tue, 17 Dec 2024 14:54:18 +0100
+Subject: [PATCH] Use single Parser for LookupHelper
+
+It is the only construction of a temporary parser, and it seems not
+necessary (anymore).
+---
+ include/cling/Interpreter/LookupHelper.h |  2 +-
+ lib/Interpreter/Interpreter.cpp          | 11 ++++-------
+ 2 files changed, 5 insertions(+), 8 deletions(-)
+
+diff --git a/include/cling/Interpreter/LookupHelper.h b/include/cling/Interpreter/LookupHelper.h
+index 6e6e281470..cd79b2a65c 100644
+--- a/include/cling/Interpreter/LookupHelper.h
++++ b/include/cling/Interpreter/LookupHelper.h
+@@ -56,7 +56,7 @@ namespace cling {
+       WithDiagnostics
+     };
+   private:
+-    std::unique_ptr<clang::Parser> m_Parser;
++    clang::Parser* m_Parser;
+     Interpreter* m_Interpreter; // we do not own.
+     std::array<const clang::Type*, kNumCachedStrings> m_StringTy = {{}};
+     /// A map containing the hash of the lookup buffer. This allows us to avoid
+diff --git a/lib/Interpreter/Interpreter.cpp b/lib/Interpreter/Interpreter.cpp
+index 13c8409cc5..f04695439b 100644
+--- a/lib/Interpreter/Interpreter.cpp
++++ b/lib/Interpreter/Interpreter.cpp
+@@ -265,13 +265,6 @@ namespace cling {
+     }
+ 
+     Sema& SemaRef = getSema();
+-    Preprocessor& PP = SemaRef.getPreprocessor();
+-
+-    m_LookupHelper.reset(new LookupHelper(new Parser(PP, SemaRef,
+-                                                     /*SkipFunctionBodies*/false,
+-                                                     /*isTemp*/true), this));
+-    if (!m_LookupHelper)
+-      return;
+ 
+     if (!isInSyntaxOnlyMode() && !m_Opts.CompilerOpts.CUDADevice) {
+       m_Executor.reset(new IncrementalExecutor(SemaRef.Diags, *getCI(),
+@@ -317,6 +310,10 @@ namespace cling {
+       return;
+     }
+ 
++    m_LookupHelper.reset(new LookupHelper(m_IncrParser->getParser(), this));
++    if (!m_LookupHelper)
++      return;
++
+     // When not using C++ modules, we now have a PCH and we can safely setup
+     // our callbacks without fearing that they get overwritten by clang code.
+     // The modules setup is handled above.
diff --git a/pkgs/by-name/cl/cling/no-clang-cpp.patch b/pkgs/by-name/cl/cling/no-clang-cpp.patch
deleted file mode 100644
index 6048037cee84f..0000000000000
--- a/pkgs/by-name/cl/cling/no-clang-cpp.patch
+++ /dev/null
@@ -1,13 +0,0 @@
-diff --git a/tools/driver/CMakeLists.txt b/tools/driver/CMakeLists.txt
-index 590d708d83..340ae529d4 100644
---- a/tools/driver/CMakeLists.txt
-+++ b/tools/driver/CMakeLists.txt
-@@ -63,7 +63,7 @@ endif()
- add_dependencies(clang clang-resource-headers)
-
- if(NOT CLANG_LINKS_TO_CREATE)
--  set(CLANG_LINKS_TO_CREATE clang++ clang-cl clang-cpp)
-+  set(CLANG_LINKS_TO_CREATE clang++ clang-cl)
- endif()
-
- foreach(link ${CLANG_LINKS_TO_CREATE})
diff --git a/pkgs/by-name/cl/cling/package.nix b/pkgs/by-name/cl/cling/package.nix
index 60cbaabe1fb9f..0bea1d522f6b2 100644
--- a/pkgs/by-name/cl/cling/package.nix
+++ b/pkgs/by-name/cl/cling/package.nix
@@ -5,13 +5,13 @@
   git,
   lib,
   libffi,
-  llvmPackages_13,
+  llvmPackages_18,
   makeWrapper,
   ncurses,
   python3,
   zlib,
 
-  # *NOT* from LLVM 13!
+  # *NOT* from LLVM 18!
   # The compiler used to compile Cling may affect the runtime include and lib
   # directories it expects to be run with. Cling builds against (a fork of) Clang,
   # so we prefer to use Clang as the compiler as well for consistency.
@@ -34,41 +34,38 @@
 let
   stdenv = clangStdenv;
 
-  # The patched clang lives in the LLVM megarepo
-  clangSrc = fetchFromGitHub {
+  version = "1.2";
+
+  clingSrc = fetchFromGitHub {
     owner = "root-project";
-    repo = "llvm-project";
-    # cling-llvm13 branch
-    rev = "3610201fbe0352a63efb5cb45f4ea4987702c735";
-    sha256 = "sha256-Cb7BvV7yobG+mkaYe7zD2KcnPvm8/vmVATNWssklXyk=";
-    sparseCheckout = [ "clang" ];
+    repo = "cling";
+    rev = "v${version}";
+    sha256 = "sha256-ay9FXANJmB/+AdnCR4WOKHuPm6P88wLqoOgiKJwJ8JM=";
   };
 
-  llvm = llvmPackages_13.llvm.override { enableSharedLibraries = false; };
-
-  unwrapped = stdenv.mkDerivation rec {
+  unwrapped = stdenv.mkDerivation {
     pname = "cling-unwrapped";
-    version = "1.0";
-
-    src = "${clangSrc}/clang";
+    inherit version;
 
-    clingSrc = fetchFromGitHub {
+    src = fetchFromGitHub {
       owner = "root-project";
-      repo = "cling";
-      rev = "v${version}";
-      sha256 = "sha256-Ye8EINzt+dyNvUIRydACXzb/xEPLm0YSkz08Xxw3xp4=";
+      repo = "llvm-project";
+      rev = "cling-llvm18-20250721-01";
+      sha256 = "sha256-JGteapyujU5w81DsfPQfTq76cYHgk5PbAFbdYfYIDo4=";
     };
 
-    prePatch = ''
-      echo "add_llvm_external_project(cling)" >> tools/CMakeLists.txt
+    preConfigure = ''
+      cp -r ${clingSrc} cling-source
 
-      cp -r $clingSrc tools/cling
-      chmod -R a+w tools/cling
-    '';
+      # Patch a bug in version 1.2 by backporting a fix. See
+      # https://github.com/root-project/cling/issues/556
+      chmod -R u+w cling-source
+      pushd cling-source
+      patch -p1 < ${./fix-new-parser.patch}
+      popd
 
-    patches = [
-      ./no-clang-cpp.patch
-    ];
+      cd llvm
+    '';
 
     nativeBuildInputs = [
       python3
@@ -84,22 +81,15 @@ let
     strictDeps = true;
 
     cmakeFlags = [
-      "-DLLVM_BINARY_DIR=${llvm.out}"
-      "-DLLVM_CONFIG=${llvm.dev}/bin/llvm-config"
-      "-DLLVM_LIBRARY_DIR=${llvm.lib}/lib"
-      "-DLLVM_MAIN_INCLUDE_DIR=${llvm.dev}/include"
-      "-DLLVM_TABLEGEN_EXE=${llvm.out}/bin/llvm-tblgen"
-      "-DLLVM_TOOLS_BINARY_DIR=${llvm.out}/bin"
-      "-DLLVM_BUILD_TOOLS=Off"
-      "-DLLVM_TOOL_CLING_BUILD=ON"
-
+      "-DLLVM_EXTERNAL_PROJECTS=cling"
+      "-DLLVM_EXTERNAL_CLING_SOURCE_DIR=../../cling-source"
+      "-DLLVM_ENABLE_PROJECTS=clang"
       "-DLLVM_TARGETS_TO_BUILD=host;NVPTX"
+      "-DLLVM_INCLUDE_TESTS=OFF"
       "-DLLVM_ENABLE_RTTI=ON"
-
-      # Setting -DCLING_INCLUDE_TESTS=ON causes the cling/tools targets to be built;
-      # see cling/tools/CMakeLists.txt
-      "-DCLING_INCLUDE_TESTS=ON"
-      "-DCLANG-TOOLS=OFF"
+    ]
+    ++ lib.optionals (!debug) [
+      "-DCMAKE_BUILD_TYPE=Release"
     ]
     ++ lib.optionals debug [
       "-DCMAKE_BUILD_TYPE=Debug"
@@ -111,11 +101,13 @@ let
 
     CPPFLAGS = if useLLVMLibcxx then [ "-stdlib=libc++" ] else [ ];
 
-    postInstall = lib.optionalString (!stdenv.hostPlatform.isDarwin) ''
+    postInstall = ''
       mkdir -p $out/share/Jupyter
-      cp -r /build/clang/tools/cling/tools/Jupyter/kernel $out/share/Jupyter
+      cp -r ../../cling-source/tools/Jupyter/kernel $out/share/Jupyter
     '';
 
+    buildTargets = [ "cling" ];
+
     dontStrip = debug;
 
     meta = with lib; {
@@ -147,18 +139,18 @@ let
     "-nostdinc++"
 
     "-resource-dir"
-    "${llvm.lib}/lib"
+    "${llvmPackages_18.llvm.lib}/lib"
 
     "-isystem"
-    "${lib.getLib unwrapped}/lib/clang/${llvmPackages_13.clang.version}/include"
+    "${lib.getLib unwrapped}/lib/clang/18/include"
   ]
   ++ lib.optionals useLLVMLibcxx [
     "-I"
-    "${lib.getDev llvmPackages_13.libcxx}/include/c++/v1"
+    "${lib.getDev llvmPackages_18.libcxx}/include/c++/v1"
     "-L"
-    "${llvmPackages_13.libcxx}/lib"
+    "${llvmPackages_18.libcxx}/lib"
     "-l"
-    "${llvmPackages_13.libcxx}/lib/libc++${stdenv.hostPlatform.extensions.sharedLibrary}"
+    "${llvmPackages_18.libcxx}/lib/libc++${stdenv.hostPlatform.extensions.sharedLibrary}"
   ]
   ++ lib.optionals (!useLLVMLibcxx) [
     "-I"