diff --git a/.cirrus.yml b/.cirrus.yml
index 56b911f13e..2d4b4bd367 100644
--- a/.cirrus.yml
+++ b/.cirrus.yml
@@ -64,24 +64,12 @@ linux_task:
   timeout_in: 60m
   environment:
     matrix:
-      - TASK_NAME_SUFFIX: x86, DMD (latest)
-        MODEL: 32
       - TASK_NAME_SUFFIX: x86, DMD (coverage)
         MODEL: 32
         << : *COVERAGE_ENVIRONMENT_TEMPLATE
-      - TASK_NAME_SUFFIX: x86, DMD (bootstrap)
-        MODEL: 32
-        HOST_DMD: dmd-2.097.1
-      - TASK_NAME_SUFFIX: x64, DMD (latest)
       # Enable this to replace coverage tests on CircleCI
       # - TASK_NAME_SUFFIX: x64, DMD (coverage)
       #   << : *COVERAGE_ENVIRONMENT_TEMPLATE
-      - TASK_NAME_SUFFIX: x64, DMD (bootstrap)
-        HOST_DMD: dmd-2.079.0
-      - TASK_NAME_SUFFIX: x64, LDC
-        HOST_DC: ldc #TODO: Update to HOST_DMD when support for HOST_DC is removed
-      - TASK_NAME_SUFFIX: x64, GDC
-        HOST_DMD: gdmd-9
   << : *COMMON_STEPS_TEMPLATE
 
 # Mac
@@ -95,23 +83,9 @@ macos13_task:
     # override Cirrus default OS (`darwin`)
     OS: osx
     matrix:
-      - TASK_NAME_SUFFIX: DMD (latest)
       - TASK_NAME_SUFFIX: DMD (coverage)
         << : *COVERAGE_ENVIRONMENT_TEMPLATE
   << : *COMMON_STEPS_TEMPLATE
-macos12_task:
-  name: macOS 12.x x64 (M1), DMD (bootstrap)
-  macos_instance:
-    image: ghcr.io/cirruslabs/macos-monterey-xcode:latest
-  timeout_in: 60m
-  environment:
-    OS_NAME: darwin
-    # override Cirrus default OS (`darwin`)
-    OS: osx
-    # de-facto bootstrap version on OSX
-    # See: https://github.com/dlang/dmd/pull/13890
-    HOST_DMD: dmd-2.099.1
-  << : *COMMON_STEPS_TEMPLATE
 
 # FreeBSD
 freebsd13_task:
diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
new file mode 100644
index 0000000000..05e2c3735b
--- /dev/null
+++ b/.github/workflows/main.yml
@@ -0,0 +1,93 @@
+# https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions
+
+name: Main
+on:
+  - pull_request # without merge conflicts
+  - push # branch or tag
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  test:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          # Linux
+          - job_name: Ubuntu 22.04 x64, DMD (latest)
+            os: ubuntu-22.04
+            host_dmd: dmd
+          - job_name: Ubuntu 22.04 x64, DMD (bootstrap)
+            os: ubuntu-22.04
+            host_dmd: dmd-2.079.0
+          - job_name: Ubuntu 22.04 x86, DMD (latest)
+            os: ubuntu-22.04
+            model: 32
+            host_dmd: dmd
+          - job_name: Ubuntu 22.04 x86, DMD (bootstrap)
+            os: ubuntu-22.04
+            model: 32
+            host_dmd: dmd-2.097.1
+          - job_name: Ubuntu 22.04 x64, LDC
+            os: ubuntu-22.04
+            host_dmd: ldc
+          - job_name: Ubuntu 22.04 x64, GDC
+            os: ubuntu-22.04
+            host_dmd: gdmd-9
+          # macOS
+          - job_name: macOS 13 x64, DMD (latest)
+            os: macos-13
+            host_dmd: dmd
+          - job_name: macOS 12 x64, DMD (bootstrap)
+            os: macos-12
+            # de-facto bootstrap version on OSX
+            # See: https://github.com/dlang/dmd/pull/13890
+            host_dmd: dmd-2.099.1
+    name: ${{ matrix.job_name }}
+    runs-on: ${{ matrix.os }}
+    timeout-minutes: 40
+    env:
+      # for ci/run.sh:
+      OS_NAME: ${{ startsWith(matrix.os, 'ubuntu') && 'linux' || (startsWith(matrix.os, 'macos') && 'darwin' || '') }}
+      MODEL: ${{ matrix.model || '64' }}
+      HOST_DMD: ${{ matrix.host_dmd }}
+      N: ${{ startsWith(matrix.os, 'macos') && '3' || '2' }}
+      FULL_BUILD: true
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 50
+      - name: Install prerequisites
+        run: ${{ runner.os == 'macOS' && 'ci/cirrusci.sh' || 'sudo -E ci/cirrusci.sh' }}
+      - name: Install host compiler
+        run: ci/run.sh install_host_compiler
+      - name: Set up repos
+        run: |
+          set -uexo pipefail
+          ln -s "$GITHUB_WORKSPACE" ../dmd
+
+          ref='${{ github.ref }}'
+          if [[ "$ref" =~ ^refs/pull/ ]]; then
+            # PR: clone the Phobos head with the same name as this DMD PR's target branch
+            # e.g., Phobos stable when targeting DMD stable
+            REPO_BRANCH="$GITHUB_BASE_REF"
+          elif [[ "$ref" =~ ^refs/(heads|tags)/(.*)$ ]]; then
+            # no PR: try to clone the Phobos head with the same name as this DMD head, falling back to master
+            # e.g., Phobos stable for a push to DMD stable, or Phobos v2.105.2 for DMD tag v2.105.2
+            REPO_BRANCH="${BASH_REMATCH[2]}"
+          else
+            echo "Error: unexpected GitHub ref '$ref'" >&2
+            exit 1
+          fi
+
+          ./ci/run.sh setup_repos "$REPO_BRANCH"
+      - name: Build
+        run: ci/run.sh build
+      - name: Test dmd
+        run: ci/run.sh test_dmd
+      - name: Test druntime
+        run: ci/run.sh test_druntime
+      - name: Test phobos
+        run: ci/run.sh test_phobos