diff --git a/.github/workflows/build-reusable.yml b/.github/workflows/build-reusable.yml
index 1ff4c62345c8..f87b4ba39097 100644
--- a/.github/workflows/build-reusable.yml
+++ b/.github/workflows/build-reusable.yml
@@ -182,6 +182,20 @@ jobs:
             package_json_arch: "x64"
             CMAKE_BUILD_TYPE: "Release"
             RELEASE_FLAGS: "-O3 -DNDEBUG=1"
+          - lto_flag: "-flto=full  -fwhole-program-vtables -fforce-emit-vtables"
+            label: bun-webkit-linux-amd64-baseline-lto
+            os: linux-x64-gh
+            package_json_arch: "x64"
+            CMAKE_BUILD_TYPE: "Release"
+            RELEASE_FLAGS: "-O3 -DNDEBUG=1"
+            MARCH_FLAG: "-march=nehalem"
+          - lto_flag: ""
+            label: bun-webkit-linux-amd64-baseline
+            os: linux-x64-gh
+            package_json_arch: "x64"
+            CMAKE_BUILD_TYPE: "Release"
+            RELEASE_FLAGS: "-O3 -DNDEBUG=1"
+            MARCH_FLAG: "-march=nehalem"
           - lto_flag: ""
             label: bun-webkit-linux-amd64-asan
             os: linux-x64-gh
@@ -218,8 +232,8 @@ jobs:
           rm -rf ${{runner.temp}}/bun-webkit ${{runner.temp}}/bun-webkit.tar.gz
           if [ "${{matrix.package_json_arch}}" = "arm64" ]; then
             export MARCH_FLAG="-march=armv8-a+crc -mtune=ampere1"
-          elif [ "${{matrix.package_json_arch}}" = "x64" ]; then
-            export MARCH_FLAG="-march=nehalem"
+          else
+            export MARCH_FLAG="${{ matrix.MARCH_FLAG || '-march=haswell' }}"
           fi
           WEBKIT_RELEASE_TYPE=${{matrix.CMAKE_BUILD_TYPE}} CPU="native" cpu=native LTO_FLAG="${{matrix.lto_flag}}" temp=${{runner.temp}} ENABLE_SANITIZERS="${{matrix.ENABLE_SANITIZERS}}" bash release.sh
           cd ${{runner.temp}}
@@ -248,6 +262,12 @@ jobs:
             package_json_arch: "x64"
             label: bun-webkit-windows-amd64-debug
             platform: x64
+          - runner: windows
+            build-type: Release
+            package_json_arch: "x64"
+            label: bun-webkit-windows-amd64-baseline
+            platform: x64
+            baseline: true
           - runner: windows-11-arm
             build-type: Release
             package_json_arch: "arm64"
@@ -312,7 +332,8 @@ jobs:
           $env:GITHUB_SHA = "${{ inputs.build_ref }}"
           $env:PACKAGE_JSON_ARCH = "${{matrix.package_json_arch}}"
           $env:GITHUB_REPOSITORY = "${{ github.repository }}"
-          ./windows-release.ps1 -Platform ${{matrix.platform}}
+          $baselineArg = if ("${{ matrix.baseline }}" -eq "true") { @("-Baseline") } else { @() }
+          ./windows-release.ps1 -Platform ${{matrix.platform}} @baselineArg
       - uses: actions/upload-artifact@v4
         with:
           name: ${{matrix.label}}
@@ -354,6 +375,18 @@ jobs:
             os: linux-x64-gh
             package_json_arch: "x64"
             CMAKE_BUILD_TYPE: "MinSizeRel"
+          - lto_flag: "-flto=full -fwhole-program-vtables -fforce-emit-vtables"
+            label: bun-webkit-linux-amd64-musl-baseline-lto
+            os: linux-x64-gh
+            package_json_arch: "x64"
+            CMAKE_BUILD_TYPE: "MinSizeRel"
+            MARCH_FLAG: "-march=nehalem"
+          - lto_flag: ""
+            label: bun-webkit-linux-amd64-musl-baseline
+            os: linux-x64-gh
+            package_json_arch: "x64"
+            CMAKE_BUILD_TYPE: "MinSizeRel"
+            MARCH_FLAG: "-march=nehalem"
     timeout-minutes: 90
     steps:
       - uses: actions/checkout@v4
@@ -373,8 +406,8 @@ jobs:
           rm -rf ${{runner.temp}}/bun-webkit ${{runner.temp}}/bun-webkit.tar.gz
           if [ "${{matrix.package_json_arch}}" = "arm64" ]; then
             export MARCH_FLAG="-march=armv8-a+crc -mtune=ampere1"
-          elif [ "${{matrix.package_json_arch}}" = "x64" ]; then
-            export MARCH_FLAG="-march=nehalem"
+          else
+            export MARCH_FLAG="${{ matrix.MARCH_FLAG || '-march=haswell' }}"
           fi
           WEBKIT_RELEASE_TYPE=${{matrix.CMAKE_BUILD_TYPE}} CPU="native" cpu=native LTO_FLAG="${{matrix.lto_flag}}" temp=${{runner.temp}} bash musl-release.sh
           cd ${{runner.temp}}
@@ -477,10 +510,22 @@ jobs:
         with:
           name: bun-webkit-linux-arm64-lto
           path: ${{runner.temp}}/bun-webkit-linux-arm64-lto
+      - uses: actions/download-artifact@v4
+        with:
+          name: bun-webkit-linux-amd64-baseline
+          path: ${{runner.temp}}/bun-webkit-linux-amd64-baseline
+      - uses: actions/download-artifact@v4
+        with:
+          name: bun-webkit-linux-amd64-baseline-lto
+          path: ${{runner.temp}}/bun-webkit-linux-amd64-baseline-lto
       - uses: actions/download-artifact@v4
         with:
           name: bun-webkit-windows-amd64
           path: ${{runner.temp}}/bun-webkit-windows-amd64
+      - uses: actions/download-artifact@v4
+        with:
+          name: bun-webkit-windows-amd64-baseline
+          path: ${{runner.temp}}/bun-webkit-windows-amd64-baseline
       - uses: actions/download-artifact@v4
         with:
           name: bun-webkit-windows-amd64-debug
@@ -517,6 +562,14 @@ jobs:
         with:
           name: bun-webkit-linux-arm64-musl-lto
           path: ${{runner.temp}}/bun-webkit-linux-arm64-musl-lto
+      - uses: actions/download-artifact@v4
+        with:
+          name: bun-webkit-linux-amd64-musl-baseline
+          path: ${{runner.temp}}/bun-webkit-linux-amd64-musl-baseline
+      - uses: actions/download-artifact@v4
+        with:
+          name: bun-webkit-linux-amd64-musl-baseline-lto
+          path: ${{runner.temp}}/bun-webkit-linux-amd64-musl-baseline-lto
 
       - name: Rename files
         run: |
@@ -541,9 +594,14 @@ jobs:
           mv ${{runner.temp}}/bun-webkit-macos-amd64-debug/bun-webkit.tar.gz ./out/bun-webkit-macos-amd64-debug.tar.gz
           mv ${{runner.temp}}/bun-webkit-linux-amd64-lto/bun-webkit.tar.gz ./out/bun-webkit-linux-amd64-lto.tar.gz
           mv ${{runner.temp}}/bun-webkit-linux-arm64-lto/bun-webkit.tar.gz ./out/bun-webkit-linux-arm64-lto.tar.gz
+          mv ${{runner.temp}}/bun-webkit-linux-amd64-baseline/bun-webkit.tar.gz ./out/bun-webkit-linux-amd64-baseline.tar.gz
+          mv ${{runner.temp}}/bun-webkit-linux-amd64-baseline-lto/bun-webkit.tar.gz ./out/bun-webkit-linux-amd64-baseline-lto.tar.gz
           mv ${{runner.temp}}/bun-webkit-linux-amd64-musl-lto/bun-webkit.tar.gz ./out/bun-webkit-linux-amd64-musl-lto.tar.gz
           mv ${{runner.temp}}/bun-webkit-linux-arm64-musl-lto/bun-webkit.tar.gz ./out/bun-webkit-linux-arm64-musl-lto.tar.gz
+          mv ${{runner.temp}}/bun-webkit-linux-amd64-musl-baseline/bun-webkit.tar.gz ./out/bun-webkit-linux-amd64-musl-baseline.tar.gz
+          mv ${{runner.temp}}/bun-webkit-linux-amd64-musl-baseline-lto/bun-webkit.tar.gz ./out/bun-webkit-linux-amd64-musl-baseline-lto.tar.gz
           mv ${{runner.temp}}/bun-webkit-windows-amd64/bun-webkit.tar.gz ./out/bun-webkit-windows-amd64.tar.gz
+          mv ${{runner.temp}}/bun-webkit-windows-amd64-baseline/bun-webkit.tar.gz ./out/bun-webkit-windows-amd64-baseline.tar.gz
           mv ${{runner.temp}}/bun-webkit-windows-amd64-debug/bun-webkit.tar.gz ./out/bun-webkit-windows-amd64-debug.tar.gz
           mv ${{runner.temp}}/bun-webkit-windows-arm64/bun-webkit.tar.gz ./out/bun-webkit-windows-arm64.tar.gz
           mv ${{runner.temp}}/bun-webkit-windows-arm64-debug/bun-webkit.tar.gz ./out/bun-webkit-windows-arm64-debug.tar.gz
@@ -568,6 +626,8 @@ jobs:
             ./out/bun-webkit-linux-arm64.tar.gz
             ./out/bun-webkit-linux-amd64-lto.tar.gz
             ./out/bun-webkit-linux-arm64-lto.tar.gz
+            ./out/bun-webkit-linux-amd64-baseline.tar.gz
+            ./out/bun-webkit-linux-amd64-baseline-lto.tar.gz
             ./out/bun-webkit-linux-amd64-asan.tar.gz
             ./out/bun-webkit-linux-arm64-asan.tar.gz
             ./out/bun-webkit-linux-amd64-debug.tar.gz
@@ -583,6 +643,8 @@ jobs:
             ./out/bun-webkit-linux-arm64-musl.tar.gz
             ./out/bun-webkit-linux-amd64-musl-lto.tar.gz
             ./out/bun-webkit-linux-arm64-musl-lto.tar.gz
+            ./out/bun-webkit-linux-amd64-musl-baseline.tar.gz
+            ./out/bun-webkit-linux-amd64-musl-baseline-lto.tar.gz
             ./out/bun-webkit-linux-amd64-musl-debug.tar.gz
             ./out/bun-webkit-linux-arm64-musl-debug.tar.gz
 
@@ -602,6 +664,7 @@ jobs:
           tag_name: ${{ inputs.release_tag }}
           files: |
             ./out/bun-webkit-windows-amd64.tar.gz
+            ./out/bun-webkit-windows-amd64-baseline.tar.gz
             ./out/bun-webkit-windows-amd64-debug.tar.gz
             ./out/bun-webkit-windows-arm64.tar.gz
             ./out/bun-webkit-windows-arm64-debug.tar.gz
diff --git a/build-icu.ps1 b/build-icu.ps1
index 78472f4cc3d6..2ceca7608c55 100644
--- a/build-icu.ps1
+++ b/build-icu.ps1
@@ -16,7 +16,9 @@ param(
     [ValidateSet("Release", "Debug")]
     [string]$BuildType = "Release",
 
-    [string]$OutputDir = ""
+    [string]$OutputDir = "",
+
+    [switch]$Baseline
 )
 
 $ErrorActionPreference = "Stop"
@@ -73,6 +75,12 @@ if (-not (Test-Path $ICU_SOURCE_DIR)) {
     if ($LASTEXITCODE -ne 0) { throw "tar failed with exit code $LASTEXITCODE" }
 }
 
+if ($Platform -eq "x64") {
+    $ArchFlag = if ($Baseline) { "/arch:SSE2" } else { "/arch:AVX2" }
+} else {
+    $ArchFlag = ""
+}
+
 # --- Function to patch vcxproj files for static library build with /MT ---
 function Patch-IcuVcxProj {
     param(
@@ -106,6 +114,10 @@ function Patch-IcuVcxProj {
         $content = $content -replace '(<PreprocessorDefinitions>)', '$1U_STATIC_IMPLEMENTATION;'
     }
 
+    if ($ArchFlag) {
+        $content = $content -replace '(<ClCompile>)', "`$1`n      <AdditionalOptions>$ArchFlag %(AdditionalOptions)</AdditionalOptions>"
+    }
+
     # Disable /GL - lld-link cannot read LTCG object files
     $content = $content -replace '<WholeProgramOptimization>true</WholeProgramOptimization>', '<WholeProgramOptimization>false</WholeProgramOptimization>'
 
diff --git a/mac-release.bash b/mac-release.bash
index 31c0e6510999..aedb064c03c6 100755
--- a/mac-release.bash
+++ b/mac-release.bash
@@ -10,7 +10,7 @@ THIS_DIR=$(pwd)
 
 # Set default values for environment variables that are not set.
 CMAKE_C_COMPILER=${CMAKE_C_COMPILER:-clang-21}
-CMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER:-clang++}
+CMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER:-clang++-21}
 CMAKE_C_FLAGS=${CMAKE_C_FLAGS:-}
 CMAKE_CXX_FLAGS=${CMAKE_CXX_FLAGS:-}
 CMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE:-Release}
diff --git a/windows-release.ps1 b/windows-release.ps1
index fab4c9b7d8b1..63c18ed15652 100644
--- a/windows-release.ps1
+++ b/windows-release.ps1
@@ -1,6 +1,8 @@
 param(
     [ValidateSet("x64", "ARM64")]
-    [string]$Platform = "x64"
+    [string]$Platform = "x64",
+
+    [switch]$Baseline
 )
 $ErrorActionPreference = "Stop"
 
@@ -41,6 +43,15 @@ clang-cl.exe --version
 $env:CC = "clang-cl"
 $env:CXX = "clang-cl"
 
+if ($Platform -eq "ARM64") {
+    $MarchFlag = "/clang:-march=armv8-a+crc /clang:-mtune=ampere1"
+} elseif ($Baseline) {
+    $MarchFlag = "/clang:-march=nehalem"
+} else {
+    $MarchFlag = "/clang:-march=haswell"
+}
+Write-Host ":: WebKit codegen floor: $MarchFlag"
+
 $output = if ($env:WEBKIT_OUTPUT_DIR) { $env:WEBKIT_OUTPUT_DIR } else { "bun-webkit" }
 $WebKitBuild = if ($env:WEBKIT_BUILD_DIR) { $env:WEBKIT_BUILD_DIR } else { "WebKitBuild" }
 $CMAKE_BUILD_TYPE = if ($env:CMAKE_BUILD_TYPE) { $env:CMAKE_BUILD_TYPE } else { "Release" }
@@ -52,7 +63,7 @@ $ICU_STATIC_LIBRARY = Join-Path $ICU_STATIC_ROOT "lib"
 $ICU_STATIC_INCLUDE_DIR = Join-Path $ICU_STATIC_ROOT "include"
 
 $ScriptDir = Split-Path -Parent $MyInvocation.MyCommand.Path
-& "$ScriptDir/build-icu.ps1" -Platform $Platform -BuildType $CMAKE_BUILD_TYPE -OutputDir $ICU_STATIC_ROOT
+& "$ScriptDir/build-icu.ps1" -Platform $Platform -BuildType $CMAKE_BUILD_TYPE -OutputDir $ICU_STATIC_ROOT -Baseline:$Baseline
 if ($LASTEXITCODE -ne 0) { throw "build-icu.ps1 failed with exit code $LASTEXITCODE" }
 
 Write-Host ":: Configuring WebKit"
@@ -108,10 +119,10 @@ cmake -S . -B $WebKitBuild `
     "-DCMAKE_C_COMPILER=${ClangPath}" `
     "-DCMAKE_CXX_COMPILER=${ClangPath}" `
     "-DCMAKE_LINKER=${LldLinkPath}" `
-    "-DCMAKE_C_FLAGS_RELEASE=/Zi /O2 /Ob2 /DNDEBUG /DU_STATIC_IMPLEMENTATION ${ARM64SehWorkaround}" `
-    "-DCMAKE_CXX_FLAGS_RELEASE=/Zi /O2 /Ob2 /DNDEBUG /DU_STATIC_IMPLEMENTATION /clang:-fno-c++-static-destructors ${ARM64SehWorkaround}" `
-    "-DCMAKE_C_FLAGS_DEBUG=/Zi /FS /O0 /Ob0 /DU_STATIC_IMPLEMENTATION ${ARM64SehWorkaround}" `
-    "-DCMAKE_CXX_FLAGS_DEBUG=/Zi /FS /O0 /Ob0 /DU_STATIC_IMPLEMENTATION /clang:-fno-c++-static-destructors ${ARM64SehWorkaround}" `
+    "-DCMAKE_C_FLAGS_RELEASE=/Zi /O2 /Ob2 /DNDEBUG /DU_STATIC_IMPLEMENTATION ${MarchFlag} ${ARM64SehWorkaround}" `
+    "-DCMAKE_CXX_FLAGS_RELEASE=/Zi /O2 /Ob2 /DNDEBUG /DU_STATIC_IMPLEMENTATION ${MarchFlag} /clang:-fno-c++-static-destructors ${ARM64SehWorkaround}" `
+    "-DCMAKE_C_FLAGS_DEBUG=/Zi /FS /O0 /Ob0 /DU_STATIC_IMPLEMENTATION ${MarchFlag} ${ARM64SehWorkaround}" `
+    "-DCMAKE_CXX_FLAGS_DEBUG=/Zi /FS /O0 /Ob0 /DU_STATIC_IMPLEMENTATION ${MarchFlag} /clang:-fno-c++-static-destructors ${ARM64SehWorkaround}" `
     -DENABLE_REMOTE_INSPECTOR=ON `
     "-DCMAKE_MSVC_RUNTIME_LIBRARY=${CmakeMsvcRuntimeLibrary}" `
     -G Ninja