diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 048167ee..151fb9d6 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -7,42 +7,45 @@ jobs:
       fail-fast: false
       max-parallel: 20
       matrix:
+        branch: [v1.4.6]
         target:
           # Unit tests
           - os: linux
             cpu: amd64
+            TEST_KIND: unit-tests
           - os: linux
             cpu: i386
+            TEST_KIND: unit-tests
           - os: macos
             cpu: amd64
+            TEST_KIND: unit-tests
           - os: windows
             cpu: i386
+            TEST_KIND: unit-tests
           - os: windows
             cpu: amd64
+            TEST_KIND: unit-tests
         include:
           - target:
               os: linux
-            builder: ubuntu-20.04
+            builder: ubuntu-18.04
           - target:
               os: macos
             builder: macos-10.15
           - target:
               os: windows
             builder: windows-2019
-
-    defaults:
-      run:
-        shell: bash
-
-    name: '${{ matrix.target.os }}-${{ matrix.target.cpu }}'
+    name: '${{ matrix.target.os }}-${{ matrix.target.cpu }} (${{ matrix.branch }})'
     runs-on: ${{ matrix.builder }}
     steps:
       - name: Checkout nim-dagger
         uses: actions/checkout@v2
         with:
+          path: nim-dagger
           submodules: true
 
       - name: Derive environment variables
+        shell: bash
         run: |
           if [[ '${{ matrix.target.cpu }}' == 'amd64' ]]; then
             ARCH=64
@@ -53,10 +56,8 @@ jobs:
           fi
           echo "ARCH=$ARCH" >> $GITHUB_ENV
           echo "PLATFORM=$PLATFORM" >> $GITHUB_ENV
-
           ncpu=
           ext=
-          MAKE_CMD="make"
           case '${{ runner.os }}' in
           'Linux')
             ncpu=$(nproc)
@@ -67,13 +68,11 @@ jobs:
           'Windows')
             ncpu=$NUMBER_OF_PROCESSORS
             ext=.exe
-            MAKE_CMD="mingw32-make"
             ;;
           esac
           [[ -z "$ncpu" || $ncpu -le 0 ]] && ncpu=1
           echo "ncpu=$ncpu" >> $GITHUB_ENV
           echo "ext=$ext" >> $GITHUB_ENV
-          echo "MAKE_CMD=${MAKE_CMD}" >> $GITHUB_ENV
 
       - name: Install build dependencies (Linux i386)
         if: runner.os == 'Linux' && matrix.target.cpu == 'i386'
@@ -115,6 +114,7 @@ jobs:
         if: >
           steps.windows-mingw-cache.outputs.cache-hit != 'true' &&
           runner.os == 'Windows'
+        shell: bash
         run: |
           mkdir -p external
           curl -L "https://nim-lang.org/download/mingw$ARCH.7z" -o "external/mingw-${{ matrix.target.cpu }}.7z"
@@ -125,6 +125,7 @@ jobs:
         if: >
           steps.windows-dlls-cache.outputs.cache-hit != 'true' &&
           runner.os == 'Windows'
+        shell: bash
         run: |
           mkdir -p external
           curl -L "https://nim-lang.org/download/windeps.zip" -o external/windeps.zip
@@ -133,33 +134,85 @@ jobs:
       - name: Path to cached dependencies (Windows)
         if: >
           runner.os == 'Windows'
+        shell: bash
         run: |
           echo "${{ github.workspace }}/external/mingw-${{ matrix.target.cpu }}/bin" >> $GITHUB_PATH
           echo "${{ github.workspace }}/external/dlls-${{ matrix.target.cpu }}" >> $GITHUB_PATH
 
+      - name: Setup environment
+        shell: bash
+        run: echo '${{ github.workspace }}/nim/bin' >> $GITHUB_PATH
+
       - name: Get latest Nim commit hash
         id: versions
+        shell: bash
         run: |
           getHash() {
             git ls-remote "https://github.com/$1" "${2:-HEAD}" | cut -f 1
           }
-          nbsHash=$(getHash status-im/nimbus-build-system)
-          echo "::set-output name=nimbus_build_system::$nbsHash"
+          nimHash=$(getHash nim-lang/Nim '${{ matrix.branch }}')
+          csourcesHash=$(getHash nim-lang/csources)
+          echo "::set-output name=nim::$nimHash"
+          echo "::set-output name=csources::$csourcesHash"
 
       - name: Restore prebuilt Nim from cache
         id: nim-cache
-        uses: actions/cache@v2
+        uses: actions/cache@v1
         with:
-          path: NimBinaries
-          key: 'NimBinaries-${{ matrix.target.os }}-${{ matrix.target.cpu }}-${{ steps.versions.outputs.nimbus_build_system }}'
+          path: nim
+          key: "nim-${{ matrix.target.os }}-${{ matrix.target.cpu }}-${{ steps.versions.outputs.nim }}"
+
+      - name: Restore prebuilt csources from cache
+        if: steps.nim-cache.outputs.cache-hit != 'true'
+        id: csources-cache
+        uses: actions/cache@v1
+        with:
+          path: csources/bin
+          key: "csources-${{ matrix.target.os }}-${{ matrix.target.cpu }}-${{ steps.versions.outputs.csources }}"
+
+      - name: Checkout Nim csources
+        if: >
+          steps.csources-cache.outputs.cache-hit != 'true' &&
+          steps.nim-cache.outputs.cache-hit != 'true'
+        uses: actions/checkout@v2
+        with:
+          repository: nim-lang/csources
+          path: csources
+          ref: ${{ steps.versions.outputs.csources }}
+
+      - name: Checkout Nim
+        if: steps.nim-cache.outputs.cache-hit != 'true'
+        uses: actions/checkout@v2
+        with:
+          repository: nim-lang/Nim
+          path: nim
+          ref: ${{ steps.versions.outputs.nim }}
 
       - name: Build Nim and associated tools
+        if: steps.nim-cache.outputs.cache-hit != 'true'
+        shell: bash
         run: |
-          curl -O -L -s -S https://raw.githubusercontent.com/status-im/nimbus-build-system/master/scripts/build_nim.sh
-          env MAKE="${MAKE_CMD} -j${ncpu}" ARCH_OVERRIDE=${PLATFORM} CC=gcc bash build_nim.sh nim csources dist/nimble NimBinaries
-          echo '${{ github.workspace }}/nim/bin' >> $GITHUB_PATH
+          [[ -z "$ncpu" || $ncpu -le 0 ]] && ncpu=1
+          if [[ ! -e csources/bin/nim$ext ]]; then
+            make -C csources -j $ncpu CC=gcc ucpu='${{ matrix.target.cpu }}'
+          else
+            echo 'Using prebuilt csources'
+          fi
+          cp -v csources/bin/nim$ext nim/bin
+          cd nim
+          nim c koch
+          ./koch boot -d:release
+          ./koch tools -d:release
+          # clean up to save cache space
+          rm koch
+          rm -rf nimcache
+          rm -rf dist
+          rm -rf .git
 
       - name: Run nim-dagger tests
+        shell: bash
         run: |
+          export UCPU="$cpu"
+          cd nim-dagger
           nimble install -y --depsOnly
           nimble test