diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 1d391a9f..6323eb7b 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -394,6 +394,7 @@ eic:
       - BUILD_IMAGE: eic_
         ENV:
         - ci
+        - ci_clang
         - ci_without_acts
         - cvmfs
         - xl
diff --git a/containers/debian/Dockerfile b/containers/debian/Dockerfile
index 0c85d2d0..679583f3 100644
--- a/containers/debian/Dockerfile
+++ b/containers/debian/Dockerfile
@@ -120,6 +120,7 @@ fi
 apt-get -yqq update
 apt-get -yqq install cpp${GCC} gcc${GCC} g++${GCC} gfortran${GCC}
 apt-get -yqq install clang${CLANG} clang-tidy${CLANG} clang-format${CLANG} libclang${CLANG}-dev libc++${CLANG}-dev
+if [ "${CLANG#-}" -ge 20 ]; then apt-get -yqq install flang${CLANG}; fi
 apt-get -yqq autoremove
 # Remove symlinks loop in nvidia/cuda:12.5.1-devel-ubuntu24.04
 rm -f /usr/bin/cpp /etc/alternatives/cpp
@@ -136,6 +137,7 @@ update-alternatives --install /usr/bin/clang-format-diff clang-format-diff /usr/
 update-alternatives --install /usr/bin/clang-tidy-diff clang-tidy-diff /usr/bin/clang-tidy-diff${CLANG}.py 100
 update-alternatives --install /usr/bin/run-clang-tidy run-clang-tidy /usr/bin/run-clang-tidy${CLANG}.py 100
 update-alternatives --install /usr/bin/llvm-config llvm-config /usr/bin/llvm-config${CLANG} 100
+if [ "${CLANG#-}" -ge 20 ]; then update-alternatives --install /usr/bin/flang flang /usr/bin/flang${CLANG} 100; fi
 # Default to gcc
 update-alternatives --install /usr/bin/cc  cc  /usr/bin/gcc 100
 update-alternatives --install /usr/bin/c++ c++ /usr/bin/g++ 100
diff --git a/spack-environment/ci_clang/epic/spack.yaml b/spack-environment/ci_clang/epic/spack.yaml
new file mode 100644
index 00000000..b06813bb
--- /dev/null
+++ b/spack-environment/ci_clang/epic/spack.yaml
@@ -0,0 +1,16 @@
+spack:
+  include:
+  - ../spack.lock
+  - ../../concretizer.yaml
+  - ../../config.yaml
+  - ../../packages.yaml
+  - ../../view.yaml
+  packages:
+    geant4:
+      require:
+      - ~opengl
+  specs:
+  - algorithms
+  - edm4eic
+  - eicrecon
+  - epic@main # EPIC_VERSION
diff --git a/spack-environment/ci_clang/spack.yaml b/spack-environment/ci_clang/spack.yaml
new file mode 100644
index 00000000..c2108b73
--- /dev/null
+++ b/spack-environment/ci_clang/spack.yaml
@@ -0,0 +1,80 @@
+spack:
+  include:
+  - ../concretizer.yaml
+  - ../config.yaml
+  - ../packages.yaml
+  - ../packages_root_without_opengl.yaml
+  - ../view.yaml
+  packages:
+    all:
+      require:
+      - '%clang'
+      - any_of: [build_system=cmake, '@:']
+      - any_of: [build_type=Release, '@:']
+  specs:
+  - acts
+  - actsvg
+  - afterburner
+  - cmake
+  - covfie
+  - dd4hep -ddeve
+  - edm4hep
+  - eigen
+  - fastjet
+  - fjcontrib
+  - fmt
+  - gaudi
+  - geant4 -opengl
+  - gfal2
+  - gfal2-util
+  - graphviz
+  - hepmc3
+  - hepmcmerger
+  - heppdt
+  - imagemagick
+  - irt
+  - iwyu
+  - jana2
+  - juggler
+  - nopayloadclient
+  - npsim -geocad
+  - onnx
+  - osg-ca-certs
+  - podio
+  - prmon
+  - pythia8
+  - py-awkward
+  - py-bokeh
+  - py-boost-histogram
+  - py-dask
+  - py-dask-histogram
+  - py-deepdiff
+  - py-eic-rucio-policy-package
+  - py-epic-capybara
+  - py-graphviz
+  - py-hepunits
+  - py-hist
+  - py-histoprint
+  - py-jinja2
+  - py-jinja2-cli
+  - py-lmfit
+  - py-lxml
+  - py-matplotlib
+  - py-mplhep
+  - py-htgettoken
+  - py-numpy
+  - py-onnx
+  - py-onnxruntime
+  - py-pandas
+  - py-particle
+  - py-pip
+  - py-rucio-clients
+  - py-scipy
+  - py-seaborn
+  - py-toml
+  - py-uproot
+  - py-vector
+  - root
+  - snakemake
+  - spdlog
+  - xrootd
diff --git a/spack-environment/packages.yaml b/spack-environment/packages.yaml
index d9a05626..27201198 100644
--- a/spack-environment/packages.yaml
+++ b/spack-environment/packages.yaml
@@ -350,6 +350,13 @@ packages:
   mosquitto:
     require:
     - '@2.0.18:'
+  mpi:
+    require:
+    - mpich
+  mpich:
+    require:
+    - '@4.2.1:'
+    - -fortran
   nlohmann-json:
     require:
     - '@3.11.2:'