diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index d93fe4fc..e63eb135 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -363,6 +363,7 @@ eic:
       - BUILD_IMAGE: eic_
         ENV:
         - ci
+        - ci_clang
         - ci_without_acts
         - xl
         BUILD_TYPE:
diff --git a/containers/debian/Dockerfile b/containers/debian/Dockerfile
index 4546e083..b2b43469 100644
--- a/containers/debian/Dockerfile
+++ b/containers/debian/Dockerfile
@@ -246,7 +246,7 @@ spack config --scope user add "config:source_cache:/var/cache/spack"
 spack config --scope user add "config:install_tree:root:/opt/software"
 spack config --scope user add "config:ccache:true"
 spack config blame config
-spack compiler find --scope site
+spack compiler find --scope site --mixed-toolchain
 spack config blame compilers
 EOF
 
diff --git a/spack-environment/ci_clang/spack.yaml b/spack-environment/ci_clang/spack.yaml
new file mode 100644
index 00000000..5e1930e6
--- /dev/null
+++ b/spack-environment/ci_clang/spack.yaml
@@ -0,0 +1,82 @@
+spack:
+  include:
+  - ../concretizer.yaml
+  - ../packages.yaml
+  - ../view.yaml
+  packages:
+    all:
+      require:
+      - '%clang'
+      - any_of: [+ipo, '@:']
+      - any_of: [build_system=cmake, '@:']
+      - any_of: [build_type=Release, '@:']
+  specs:
+  - acts
+  - actsvg
+  - afterburner
+  - algorithms
+  - cmake
+  - covfie
+  - dd4hep -ddeve
+  - edm4eic
+  - edm4hep
+  - eicrecon
+  - eigen
+  - epic@main # EPIC_VERSION
+  - 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-seaborn
+  - py-toml
+  - py-uproot
+  - py-vector
+  - root -opengl -webgui
+  - snakemake
+  - spdlog
+  - xrootd
diff --git a/spack-environment/packages.yaml b/spack-environment/packages.yaml
index b13d8bfd..fab64a5a 100644
--- a/spack-environment/packages.yaml
+++ b/spack-environment/packages.yaml
@@ -264,6 +264,13 @@ packages:
   mosquitto:
     require:
     - '@2.0.18:'
+  mpi:
+    require:
+    - mpich
+  mpich:
+    require:
+    - '@4.2.1'
+    - -fortran
   nlohmann-json:
     require:
     - '@3.11.2:'