diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 5f3807ec889..dacd4e7bb01 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -4,7 +4,7 @@ on:
   pull_request:
     branches: [ develop, master ]
   push:
-    branches: [ develop ]
+    branches: [ develop, arm-ci ]
     paths-ignore:
       - 'doygen/**'
       - 'hooks/**'
@@ -19,165 +19,21 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
-  prim-rev:
-    name: prim and rev tests
-    runs-on: windows-latest
-
-    steps:
-    - uses: actions/checkout@v4
-    - uses: actions/setup-python@v5
-      with:
-        python-version: '3.x'
-    - uses: r-lib/actions/setup-r@v2
-      with:
-        r-version: 'release'
-        rtools-version: '44'
-
-    - name: Set path for Rtools44
-      if: runner.os == 'Windows'
-      run: echo "C:/rtools44/usr/bin;C:/rtools44/x86_64-w64-mingw32.static.posix/bin" | Out-File -Append -FilePath $env:GITHUB_PATH -Encoding utf8
-
-    - name: Build Math libs
-      shell: powershell
-      run: |
-        make -f make/standalone math-libs -j2
-    - name: Add TBB to PATH
-      shell: powershell
-      run: echo "D:/a/math/math/lib/tbb" | Out-File -Append -FilePath $env:GITHUB_PATH -Encoding utf8
-    - name: Run prim and rev unit tests
-      shell: powershell
-      run: |
-        python.exe runTests.py -j2 test/unit/*_test.cpp
-        python.exe runTests.py -j2 test/unit/math/*_test.cpp
-        python.exe runTests.py -j2 test/unit/math/prim
-        python.exe runTests.py -j2 test/unit/math/rev
-        python.exe runTests.py -j2 test/unit/math/memory
-
-    - name: Upload gtest_output xml
-      uses: actions/upload-artifact@v4
-      if: failure()
-      with:
-        name: gtest_outputs_xml
-        path: '**/*_test.xml'
-
-  fwd-non-fun-mix:
-    name: fwd tests and non-fun mix tests
-    runs-on: windows-latest
-
-    steps:
-    - uses: actions/checkout@v4
-    - uses: actions/setup-python@v5
-      with:
-        python-version: '3.x'
-    - uses: r-lib/actions/setup-r@v2
-      with:
-        r-version: 'release'
-        rtools-version: '44'
-
-    - name: Set path for Rtools44
-      if: runner.os == 'Windows'
-      run: echo "C:/rtools44/usr/bin;C:/rtools44/x86_64-w64-mingw32.static.posix/bin" | Out-File -Append -FilePath $env:GITHUB_PATH -Encoding utf8
-
-    - name: Build Math libs
-      shell: powershell
-      run: |
-        make -f make/standalone math-libs -j2
-    - name: Add TBB to PATH
-      shell: powershell
-      run: echo "D:/a/math/math/lib/tbb" | Out-File -Append -FilePath $env:GITHUB_PATH -Encoding utf8
-    - name: Disable running fwd/mix tests
-      shell: powershell
-      run: echo "CXXFLAGS+= -DSTAN_MATH_TESTS_REV_ONLY" | Out-File -Append -FilePath make/local -Encoding utf8
-    - name: Run fwd unit tests and all the mix tests except those in mix/fun
-      shell: powershell
-      run: |
-        python.exe runTests.py test/unit/math/fwd -j2
-        python.exe runTests.py test/unit/math/mix/core -j2
-        python.exe runTests.py test/unit/math/mix/functor -j2
-        python.exe runTests.py test/unit/math/mix/meta -j2
-        python.exe runTests.py test/unit/math/mix/prob -j2
-        python.exe runTests.py test/unit/math/mix/*_test.cpp -j2
-
-    - name: Upload gtest_output xml
-      uses: actions/upload-artifact@v4
-      if: failure()
-      with:
-        name: gtest_outputs_xml
-        path: '**/*_test.xml'
-
   mix-fun-1:
     name: mix/fun tests 1
-    runs-on: windows-latest
+    runs-on: ubuntu-24.04-arm
 
     steps:
     - uses: actions/checkout@v4
     - uses: actions/setup-python@v5
       with:
         python-version: '3.x'
-    - uses: r-lib/actions/setup-r@v2
-      with:
-        r-version: 'release'
-        rtools-version: '44'
-
-    - name: Set path for Rtools44
-      if: runner.os == 'Windows'
-      run: echo "C:/rtools44/usr/bin;C:/rtools44/x86_64-w64-mingw32.static.posix/bin" | Out-File -Append -FilePath $env:GITHUB_PATH -Encoding utf8
-
-    - name: Build Math libs
-      shell: powershell
-      run: |
-        make -f make/standalone math-libs -j2
-    - name: Add TBB to PATH
-      shell: powershell
-      run: echo "D:/a/math/math/lib/tbb" | Out-File -Append -FilePath $env:GITHUB_PATH -Encoding utf8
-    - name: Run mix/fun unit tests
-      shell: powershell
-      run: |
-        $MixFunTests = Get-ChildItem -Path test\unit\math\mix\fun\* -Include *.cpp | Resolve-Path -Relative
-        $NumberTests = $MixFunTests.Length
-        $HalfNumberTests = [math]::Floor($NumberTests / 2)
-        python.exe runTests.py $MixFunTests[0..$HalfNumberTests]
-
-    - name: Upload gtest_output xml
-      uses: actions/upload-artifact@v4
-      if: failure()
-      with:
-        name: gtest_outputs_xml
-        path: '**/*_test.xml'
-
-  mix-fun-2:
-    name: mix/fun tests 2
-    runs-on: windows-latest
-
-    steps:
-    - uses: actions/checkout@v4
-    - uses: actions/setup-python@v5
-      with:
-        python-version: '3.x'
-    - uses: r-lib/actions/setup-r@v2
-      with:
-        r-version: 'release'
-        rtools-version: '44'
-
-    - name: Set path for Rtools44
-      if: runner.os == 'Windows'
-      run: echo "C:/rtools44/usr/bin;C:/rtools44/x86_64-w64-mingw32.static.posix/bin" | Out-File -Append -FilePath $env:GITHUB_PATH -Encoding utf8
-
     - name: Build Math libs
-      shell: powershell
       run: |
-        Add-Content make\local "O=1`n"
         make -f make/standalone math-libs -j2
-    - name: Add TBB to PATH
-      shell: powershell
-      run: echo "D:/a/math/math/lib/tbb" | Out-File -Append -FilePath $env:GITHUB_PATH -Encoding utf8
     - name: Run mix/fun unit tests
-      shell: powershell
       run: |
-        $MixFunTests = Get-ChildItem -Path test\unit\math\mix\fun\* -Include *.cpp | Resolve-Path -Relative
-        $NumberTests = $MixFunTests.Length
-        $HalfNumberTests = [math]::Floor($NumberTests / 2)
-        python.exe runTests.py $MixFunTests[($HalfNumberTests + 1)..($NumberTests - 1)]
+        python runTests.py -j4 test/unit/math/mix/fun
 
     - name: Upload gtest_output xml
       uses: actions/upload-artifact@v4