diff --git a/.github/workflows/linux.yml b/.github/workflows/linux.yml
index d30d592b6cd1..2861a0a0ba20 100644
--- a/.github/workflows/linux.yml
+++ b/.github/workflows/linux.yml
@@ -21,17 +21,21 @@ jobs:
     env:
       ARCH: x86_64
       ARCH_CMD: linux64
-      DOCKER_TEST_PREFIX: crystallang/crystal:${{ matrix.crystal_bootstrap_version }}
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
       matrix:
-        flags: [""]
+        env:
+          - FLAGS: ""
+          - FLAGS: "-Devloop=libevent"
+          - FLAGS: "-Dpreview_mt -Dexecution_context"
         include:
-          # libffi is only available starting from the 1.2.2 build images
-          - crystal_bootstrap_version: 1.0.0
-            flags: "FLAGS=-Dwithout_ffi USE_PCRE1=true"
-          - crystal_bootstrap_version: 1.18.2 # LATEST RELEASE
+          - env:
+              CRYSTAL_BOOTSTRAP_VERSION: 1.0.0
+              # libffi is only available starting from the 1.2.2 build images
+              FLAGS: "-Dwithout_ffi"
+              # pcre2 is only available starting from the 1.8.0 build images
+              USE_PCRE1: true
     steps:
       - name: Download Crystal source
         uses: actions/checkout@v5
@@ -45,13 +49,21 @@ jobs:
         run: bin/ci prepare_build
 
       - name: Test
-        run: ${{ matrix.flags }} bin/ci build
+        run: bin/ci build
+        env: ${{ matrix.env }}
 
   x86_64-musl-test:
     env:
       ARCH: x86_64-musl
       ARCH_CMD: linux64
     runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        env:
+          - FLAGS: ""
+          - FLAGS: "-Devloop=libevent"
+          - FLAGS: "-Dpreview_mt -Dexecution_context"
     steps:
       - name: Download Crystal source
         uses: actions/checkout@v5
@@ -66,29 +78,7 @@ jobs:
 
       - name: Test
         run: bin/ci build
-
-  x86_64-gnu-test-preview_mt:
-    env:
-      ARCH: x86_64
-      ARCH_CMD: linux64
-    runs-on: ubuntu-latest
-    steps:
-      - name: Download Crystal source
-        uses: actions/checkout@v5
-        with:
-          persist-credentials: false
-
-      - name: Prepare System
-        run: bin/ci prepare_system
-
-      - name: Prepare Build
-        run: bin/ci prepare_build
-
-      - name: Make Crystal
-        run: bin/ci with_build_env 'make crystal'
-
-      - name: Test
-        run: bin/ci with_build_env 'CRYSTAL_WORKERS=4 make std_spec threads=1 FLAGS="-D preview_mt"'
+        env: ${{ matrix.env }}
 
   check_format:
     env:
diff --git a/.github/workflows/macos.yml b/.github/workflows/macos.yml
index 191e66ec988d..53660a2e43ef 100644
--- a/.github/workflows/macos.yml
+++ b/.github/workflows/macos.yml
@@ -15,16 +15,13 @@ env:
 jobs:
   darwin-test:
     runs-on: ${{ matrix.runs-on }}
-    name: "${{ matrix.runs-on }} (${{ matrix.arch }})"
     strategy:
       matrix:
-        include:
-        - runs-on: macos-15-intel
-          arch: x86_64-darwin
-        - runs-on: macos-14
-          arch: aarch64-darwin
-        - runs-on: macos-15
-          arch: aarch64-darwin
+        runs-on: [macos-15-intel, macos-15]
+        env:
+          - FLAGS: ""
+          - FLAGS: "-Devloop=libevent"
+          - FLAGS: "-Dpreview_mt -Dexecution_context"
       fail-fast: false
     steps:
       - name: Download Crystal source
@@ -50,6 +47,8 @@ jobs:
 
       - name: Test
         run: bin/ci build
+        env: ${{ matrix.env }}
 
       - name: Test interpreter
         run: bin/ci with_build_env 'make interpreter_spec'
+        env: ${{ matrix.env }}
diff --git a/.github/workflows/mingw-w64-steps.yml b/.github/workflows/mingw-w64-steps.yml
index f4740a9c425f..41595e197166 100644
--- a/.github/workflows/mingw-w64-steps.yml
+++ b/.github/workflows/mingw-w64-steps.yml
@@ -81,6 +81,12 @@ jobs:
 
   test-stdlib:
     runs-on: ${{ inputs.runs-on }}
+    strategy:
+      fail-fast: false
+      matrix:
+        env:
+          - FLAGS: ""
+          - FLAGS: "-Dpreview_mt -Dexecution_context"
     steps:
       - name: Setup MSYS2
         id: msys2
@@ -109,6 +115,7 @@ jobs:
         run: |
           export CRYSTAL_SPEC_COMPILER_BIN="$(which crystal.exe)"
           make std_spec
+        env: ${{ matrix.env }}
 
   test-compiler:
     runs-on: ${{ inputs.runs-on }}
diff --git a/.github/workflows/smoke.yml b/.github/workflows/smoke.yml
index c16cb6101cb1..f3efa74d52db 100644
--- a/.github/workflows/smoke.yml
+++ b/.github/workflows/smoke.yml
@@ -57,7 +57,6 @@ env:
 
 jobs:
   smoke-test:
-    name: ${{ matrix.target }}
     runs-on: ubuntu-latest
 
     strategy:
@@ -74,6 +73,13 @@ jobs:
           - x86_64-netbsd
           - x86_64-openbsd
           - x86_64-solaris
+        env:
+          - FLAGS: ""
+          - FLAGS: "-Dpreview_mt -Dexecution_context"
+        include:
+          - target: x86_64-freebsd
+            env:
+              FLAGS: "-Devloop=libevent"
 
     steps:
       - name: Download Crystal source
@@ -86,3 +92,4 @@ jobs:
 
       - name: Run smoke test
         run: bin/ci with_build_env make smoke_test target=${{ matrix.target }}
+        env: ${{ matrix.env }}
diff --git a/.github/workflows/win.yml b/.github/workflows/win.yml
index 2d2f9a3bcc00..ba589236757b 100644
--- a/.github/workflows/win.yml
+++ b/.github/workflows/win.yml
@@ -228,6 +228,13 @@ jobs:
   x86_64-windows-test:
     runs-on: windows-2025
     needs: [x86_64-windows-release]
+    strategy:
+      fail-fast: false
+      matrix:
+        env:
+          - FLAGS: ""
+          - FLAGS: "-Dpreview_mt -Dexecution_context"
+    env: ${{ matrix.env }}
     steps:
       - name: Disable CRLF line ending substitution
         run: |
diff --git a/bin/ci b/bin/ci
index fabeae18cbab..a47600b5c952 100755
--- a/bin/ci
+++ b/bin/ci
@@ -189,7 +189,7 @@ with_build_env() {
 
   on_linux verify_linux_environment
 
-  export DOCKER_TEST_PREFIX="${DOCKER_TEST_PREFIX:=crystallang/crystal:1.18.2}"
+  export DOCKER_TEST_PREFIX="${DOCKER_TEST_PREFIX:="crystallang/crystal:${CRYSTAL_BOOTSTRAP_VERSION:-1.18.2}"}"
 
   case $ARCH in
     x86_64)