diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..0e4897d
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,152 @@
+name: CI
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+
+jobs:
+  # -------------------------------------------
+  # 1) CI Format job
+  # -------------------------------------------
+  ci_format:
+    # If you want to skip if the PR title has 'Draft:' or 'WIP:',
+    # you can approximate with the condition below.
+    if: >
+      github.event_name == 'pull_request' &&
+      (!
+        (
+          contains(github.event.pull_request.title, 'Draft:') ||
+          contains(github.event.pull_request.title, 'WIP:')
+        )
+      ) ||
+      github.event_name == 'push'
+    runs-on: ubuntu-latest
+
+    # If you need HPC resources, set up a self-hosted runner here:
+    # runs-on: self-hosted
+    # or
+    # runs-on: [self-hosted, darwin-slurm-shared]
+
+    # Equivalent to 'variables:' in GitLab
+    env:
+      GIT_SUBMODULE_STRATEGY: recursive
+      SCHEDULER_PARAMETERS: "--nodes 1 --partition=skylake-gold"
+
+    steps:
+      - name: Check out code (with submodules)
+        uses: actions/checkout@v3
+        with:
+          submodules: true
+
+      - name: Set up environment
+        run: |
+          source env/bash
+
+      - name: Format
+        run: |
+          VERBOSE=1 ./style/format.sh
+
+      - name: Check for changes
+        run: |
+          git diff --exit-code --ignore-submodules
+
+  # -------------------------------------------
+  # 2) CI CPU job
+  # -------------------------------------------
+  ci_cpu:
+    # If you wanted it to run only if ci_format succeeded:
+    needs: ci_format
+    # Or skip if 'Draft:' or 'WIP:' in PR title
+    if: >
+      github.event_name == 'pull_request' &&
+      (!
+        (
+          contains(github.event.pull_request.title, 'Draft:') ||
+          contains(github.event.pull_request.title, 'WIP:')
+        )
+      ) ||
+      github.event_name == 'push'
+    runs-on: ubuntu-latest
+    env:
+      GIT_SUBMODULE_STRATEGY: recursive
+      SCHEDULER_PARAMETERS: "--nodes 1 --partition=skylake-gold"
+
+    steps:
+      - name: Check out code (with submodules)
+        uses: actions/checkout@v3
+        with:
+          submodules: true
+
+      - name: Set up environment
+        run: |
+          source env/bash
+
+      - name: Build Jaybenne
+        run: |
+          build_jaybenne
+
+      - name: stepdiff tests
+        run: |
+          cd tst
+          ./stepdiff.py --executable ../build_darwin-skylake-gold/mcblock \
+                        --input ../inputs/stepdiff.in --use_mpiexec
+          ./stepdiff.py --executable ../build_darwin-skylake-gold/mcblock \
+                        --input ../inputs/stepdiff_ddmc.in --use_mpiexec
+          ./stepdiff_smr.py --executable ../build_darwin-skylake-gold/mcblock \
+                            --input ../inputs/stepdiff_smr.in --use_mpiexec
+          ./stepdiff_smr.py --executable ../build_darwin-skylake-gold/mcblock \
+                            --input ../inputs/stepdiff_smr_ddmc.in --use_mpiexec
+          ./stepdiff_smr.py --executable ../build_darwin-skylake-gold/mcblock \
+                            --input ../inputs/stepdiff_smr_ddmc.in --use_mpiexec --mpi_nthreads 8
+          ./stepdiff_smr.py --executable ../build_darwin-skylake-gold/mcblock \
+                            --input ../inputs/stepdiff_smr_hybrid.in --use_mpiexec
+          ./stepdiff_smr.py --executable ../build_darwin-skylake-gold/mcblock \
+                            --input ../inputs/stepdiff_smr_hybrid.in --use_mpiexec --mpi_nthreads 8
+
+  # -------------------------------------------
+  # 3) CI GPU job
+  # -------------------------------------------
+  ci_gpu:
+    needs: ci_format
+    if: >
+      github.event_name == 'pull_request' &&
+      (!
+        (
+          contains(github.event.pull_request.title, 'Draft:') ||
+          contains(github.event.pull_request.title, 'WIP:')
+        )
+      ) ||
+      github.event_name == 'push'
+    runs-on: ubuntu-latest
+    env:
+      GIT_SUBMODULE_STRATEGY: recursive
+      SCHEDULER_PARAMETERS: "--nodes 1 --partition=volta-x86"
+
+    steps:
+      - name: Check out code (with submodules)
+        uses: actions/checkout@v3
+        with:
+          submodules: true
+
+      - name: Set up environment
+        run: |
+          source env/bash
+
+      - name: Build Jaybenne
+        run: |
+          build_jaybenne
+
+      - name: stepdiff GPU tests
+        run: |
+          cd tst
+          ./stepdiff.py --executable ../build_darwin-volta-x86/mcblock \
+                        --input ../inputs/stepdiff.in --use_mpiexec
+          ./stepdiff.py --executable ../build_darwin-volta-x86/mcblock \
+                        --input ../inputs/stepdiff_ddmc.in --use_mpiexec
+          ./stepdiff_smr.py --executable ../build_darwin-volta-x86/mcblock \
+                            --input ../inputs/stepdiff_smr.in --use_mpiexec
+          ./stepdiff_smr.py --executable ../build_darwin-volta-x86/mcblock \
+                            --input ../inputs/stepdiff_smr_ddmc.in --use_mpiexec
+          ./stepdiff_smr.py --executable ../build_darwin-volta-x86/mcblock \
+                            --input ../inputs/stepdiff_smr_hybrid.in --use_mpiexec
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
deleted file mode 100644
index fce8aca..0000000
--- a/.gitlab-ci.yml
+++ /dev/null
@@ -1,82 +0,0 @@
-# ========================================================================================
-#  (C) (or copyright) 2023-2024. Triad National Security, LLC. All rights reserved.
-#
-#  This program was produced under U.S. Government contract 89233218CNA000001 for Los
-#  Alamos National Laboratory (LANL), which is operated by Triad National Security, LLC
-#  for the U.S. Department of Energy/National Nuclear Security Administration. All rights
-#  in the program are reserved by Triad National Security, LLC, and the U.S. Department
-#  of Energy/National Nuclear Security Administration. The Government is granted for
-#  itself and others acting on its behalf a nonexclusive, paid-up, irrevocable worldwide
-#  license in this material to reproduce, prepare derivative works, distribute copies to
-#  the public, perform publicly and display publicly, and to permit others to do so.
-# ========================================================================================
-
-# NOTE(@pdmullen): The following is largely borrowed from the open-source AthenaK
-# software, adapted to LANL Darwin runners
-
-variables:
-  GIT_SUBMODULE_STRATEGY: recursive
-
-stages:
-  - ci_format
-  - ci_cpu
-  - ci_gpu
-
-default:
-  tags:
-    - darwin-slurm-shared
-
-.default-job:
-  rules:
-    - if: '$CI_MERGE_REQUEST_TITLE =~ /Draft:/ || $CI_MERGE_REQUEST_TITLE =~ /WIP:/'
-      when: never
-    - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
-  id_tokens:
-    SITE_ID_TOKEN:
-      aud: https://gitlab.lanl.gov
-
-ci_format-job:
-  extends: .default-job
-  stage: ci_format
-  variables:
-    SCHEDULER_PARAMETERS: "--nodes 1 --partition=skylake-gold"
-  script:
-    - cd $CI_PROJECT_DIR
-    - source env/bash
-    - VERBOSE=1 ./style/format.sh
-    - git diff --exit-code --ignore-submodules
-
-ci_cpu-job:
-  extends: .default-job
-  stage: ci_cpu
-  variables:
-    SCHEDULER_PARAMETERS: "--nodes 1 --partition=skylake-gold"
-  script:
-    - cd $CI_PROJECT_DIR
-    - source env/bash
-    - build_jaybenne
-    - cd ../tst
-    - ./stepdiff.py --executable ../build_darwin-skylake-gold/mcblock --input ../inputs/stepdiff.in --use_mpiexec
-    - ./stepdiff.py --executable ../build_darwin-skylake-gold/mcblock --input ../inputs/stepdiff_ddmc.in --use_mpiexec
-    - ./stepdiff_smr.py --executable ../build_darwin-skylake-gold/mcblock --input ../inputs/stepdiff_smr.in --use_mpiexec
-    - ./stepdiff_smr.py --executable ../build_darwin-skylake-gold/mcblock --input ../inputs/stepdiff_smr_ddmc.in --use_mpiexec
-    - ./stepdiff_smr.py --executable ../build_darwin-skylake-gold/mcblock --input ../inputs/stepdiff_smr_ddmc.in --use_mpiexec --mpi_nthreads 8
-    - ./stepdiff_smr.py --executable ../build_darwin-skylake-gold/mcblock --input ../inputs/stepdiff_smr_hybrid.in --use_mpiexec
-    - ./stepdiff_smr.py --executable ../build_darwin-skylake-gold/mcblock --input ../inputs/stepdiff_smr_hybrid.in --use_mpiexec --mpi_nthreads 8
-
-
-ci_gpu-job:
-  extends: .default-job
-  stage: ci_gpu
-  variables:
-    SCHEDULER_PARAMETERS: "--nodes 1 --partition=volta-x86"
-  script:
-    - cd $CI_PROJECT_DIR
-    - source env/bash
-    - build_jaybenne
-    - cd ../tst
-    - ./stepdiff.py --executable ../build_darwin-volta-x86/mcblock --input ../inputs/stepdiff.in --use_mpiexec
-    - ./stepdiff.py --executable ../build_darwin-volta-x86/mcblock --input ../inputs/stepdiff_ddmc.in --use_mpiexec
-    - ./stepdiff_smr.py --executable ../build_darwin-volta-x86/mcblock --input ../inputs/stepdiff_smr.in --use_mpiexec
-    - ./stepdiff_smr.py --executable ../build_darwin-volta-x86/mcblock --input ../inputs/stepdiff_smr_ddmc.in --use_mpiexec
-    - ./stepdiff_smr.py --executable ../build_darwin-volta-x86/mcblock --input ../inputs/stepdiff_smr_hybrid.in --use_mpiexec
diff --git a/.gitlab/merge_request_templates/Default.md b/.gitlab/merge_request_templates/Default.md
deleted file mode 100644
index 9d49f05..0000000
--- a/.gitlab/merge_request_templates/Default.md
+++ /dev/null
@@ -1,17 +0,0 @@
-### Background
-
-* item
-
-### Purpose of Pull Request
-
-* detail
-
-### Description of changes
-
-* item
-
-### Status
-
-* Required checks:
-  - [ ] CI passes
-  - [ ] At least one approval
diff --git a/external/singularity-opac b/external/singularity-opac
index b4542ed..b61be52 160000
--- a/external/singularity-opac
+++ b/external/singularity-opac
@@ -1 +1 @@
-Subproject commit b4542ed7cd618e6ad0d9331205f7ed3d0c2e3a0d
+Subproject commit b61be5226fee505d05ffeb6419408740792b51c7