diff --git a/.github/workflows/build_spack.yml b/.github/workflows/build_spack.yml
index d5fbee8..b6de43e 100644
--- a/.github/workflows/build_spack.yml
+++ b/.github/workflows/build_spack.yml
@@ -17,10 +17,22 @@ jobs:
       fail-fast: false
       matrix:
         include:
+
+         - os: macos-14
+           xcode: "15.0.1"
+           compiler: "apple-clang@15.0.0"
+           publish: false
+
          - os: macos-14
            xcode: "16.0.0"
+           compiler: "apple-clang@16.0.0"
+           publish: true
+
          - os: macos-15
            xcode: "16.0.0"
+           compiler: "apple-clang@16.0.0"
+           publish: true
+
     uses: ./.github/workflows/spack.yml
     with:
       os: ${{ matrix.os }}
@@ -31,9 +43,20 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os:
-         - ubuntu-22.04
-         - ubuntu-24.04
+        include:
+
+         - os: ubuntu-22.04
+           compiler: gcc@12.3.0
+           publish: true
+
+         - os: ubuntu-24.04
+           compiler: gcc@13.2.0
+           publish: true
+
+         - os: ubuntu-24.04
+           compiler: clang@18.1.3
+           publish: false
+
     uses: ./.github/workflows/spack.yml
     with:
       os: ${{ matrix.os }}
@@ -43,8 +66,12 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        image:
-          - ghcr.io/acts-project/alma9-base:67
+
+        include:
+          - image: ghcr.io/acts-project/alma9-base:67
+            compiler: gcc@11.4.1
+            publish: true
+
     uses: ./.github/workflows/spack.yml
     with:
       os: ubuntu-latest
diff --git a/.github/workflows/spack.yml b/.github/workflows/spack.yml
index 893d66d..2b8fedf 100644
--- a/.github/workflows/spack.yml
+++ b/.github/workflows/spack.yml
@@ -14,10 +14,14 @@ on:
         required: false
         type: string
         default: "latest-stable"
+      compiler:
+        required: false
+        type: string
+        default: ""
       publish:
         required: false
         type: boolean
-        default: true
+        default: false
 
 jobs:
 
@@ -38,7 +42,8 @@ jobs:
           git config user.email 41898282+github-actions[bot]@users.noreply.github.com
           curl https://patch-diff.githubusercontent.com/raw/spack/spack/pull/47370.patch | git am
 
-      - run: |
+      - name: List visible compilers
+        run: |
           spack compiler find
           spack compilers
 
@@ -74,6 +79,11 @@ jobs:
           rm -rf /usr/share/dotnet/
           df -h
 
+      - name: Select compiler
+        if: inputs.compiler != ''
+        run: |
+          spack -e .config add 'packages:all:compiler: ["%${{ inputs.compiler }}"]'
+
       - name: Spack concretize
         run: |
           spack -e . concretize -Uf
@@ -102,12 +112,16 @@ jobs:
 
       - name: Derive target triplet
         run: |
-          echo "TARGET_TRIPLET=$(spack arch --family)" >> "$GITHUB_ENV"
+          if [ "${{ inputs.compiler }}" != "" ]; then
+            echo "TARGET_TRIPLET=$(spack arch --family)_${{ inputs.compiler }}" >> "$GITHUB_ENV"
+          else
+            echo "TARGET_TRIPLET=$(spack arch --family)" >> "$GITHUB_ENV"
+          fi
 
       - name: Copy spack.lock to target-triplet
         run: |
           echo "TARGET_TRIPLET=${TARGET_TRIPLET}" >> "$GITHUB_ENV"
-          cp spack.lock "spack-${TARGET_TRIPLET}.lock"
+          cp spack.lock "spack_${TARGET_TRIPLET}.lock"
 
       - name: Upload lock files
         if: inputs.publish
@@ -115,7 +129,7 @@ jobs:
         with:
           name: spack-${{ env.TARGET_TRIPLET }}-locks
           path: |
-            spack-*.lock
+            spack_*.lock
           if-no-files-found: error
 
       - name: Add lock files to release
@@ -123,7 +137,7 @@ jobs:
         if: inputs.publish && startsWith(github.ref, 'refs/tags/')
         with:
           files: |
-            spack-*.lock
+            spack_*.lock
 
       - name: Push packages and update index
         if: (github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/tags/')) && !cancelled()