diff --git a/.bazelrc b/.bazelrc
index c75186b55b5..f3b086bf580 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -219,12 +219,7 @@ build:macos --copt='-femit-dwarf-unwind=no-compact-unwind'
 # an effect. On macOS we build some ObjC as part of Dawn, set this flag to an empty string so we
 # can set the right configuration flags.
 # TODO(soon): File a bazel issue for the flag so we can drop this.
-build:macos --experimental_objc_fastbuild_options=''
-
-# Unfortunately experimental_objc_fastbuild_options does not respect options set before and
-# overwrites them. This causes mysterious binary size bloat for fastbuild-based configurations on
-# macOS when enabling some optimizations. Turn it in into a no-op.
-build:mac --experimental_objc_fastbuild_options=""
+build:macos --experimental_objc_fastbuild_options=""
 
 # On Linux, always link libc++ statically to avoid compatibility issues with different OS versions.
 # macOS links with dynamic libc++ by default, which has good backwards compatibility.
@@ -318,6 +313,17 @@ build:release_macos --config=release_unix
 build:release_macos --linkopt="-Wl,-no_data_in_code_info"
 build:release_macos --linkopt="-Wl,-no_function_starts"
 
+# On macOS, optionally compile using LLD (19 or higher is compatible with the default flags added by
+# apple_support). Requires Homebrew's lld package to be installed. This is less CPU intensive than
+# the system linker, but also slightly slower in terms of wall time since it is less parallel. More
+# importantly, it allows us to enable LLD's ICF pass, which significantly decreases binary sizes.
+# We could use Xcode 16's -Wl,-deduplicate option instead, but LLD's ICF appears to be superior.
+# We also want to enable ICF for Linux, but there it causes warnings when dynamically linking with
+# libc++.
+build:macos_lld --linkopt="-fuse-ld=/opt/homebrew/bin/ld64.lld"
+build:macos_lld_icf --config=macos_lld
+build:macos_lld_icf --linkopt="-Wl,--icf=safe"
+
 build:release_windows --config=release
 # Windows uses /O2 as its preferred optimization setting and enabled by bazel in the opt
 # configuration, but for clang-cl this is equivalent to only -O2 and a few other things. -O3 is
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 99063ace919..2dd4378054a 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -96,6 +96,10 @@ jobs:
         if: runner.os == 'macOS'
         run: |
           sudo xcode-select -s "/Applications/Xcode_15.1.app"
+          # Install lld
+          brew install lld
+          # Enable lld identical code folding to significantly reduce binary size.
+          echo "build:macos --config=macos_lld_icf" >> .bazelrc
       - name: Setup Windows
         if: runner.os == 'Windows'
         run: |
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index fecddeb1ea3..5284188acbd 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -19,16 +19,16 @@ jobs:
   fixup:
     if: github.event_name == 'pull_request'
     uses: ./.github/workflows/fixup.yml
-  labels:    
+  labels:
     if: github.event_name == 'pull_request'
-    uses: ./.github/workflows/labels.yml 
+    uses: ./.github/workflows/labels.yml
   test:
     strategy:
       matrix:
         os:
           [
             { name : linux, image : ubuntu-20.04 },
-            { name : macOS, image : macos-13 },
+            { name : macOS, image : macos-15 },
             { name : windows, image : windows-2022 }
           ]
         config:
@@ -62,7 +62,7 @@ jobs:
             config: { suffix: -debug, bazel-args: --config=debug }
           # due to resource constraints, exclude the macOS-debug runner for now. linux-debug and
           # linux-asan should provide sufficient coverage for building in the debug configuration.
-          - os:     { name : macOS, image : macos-13 }
+          - os:     { name : macOS, image : macos-15 }
             config: { suffix: -debug, bazel-args: --config=debug }
       fail-fast: false
     runs-on: ${{ matrix.os.image }}
@@ -103,17 +103,15 @@ jobs:
           sed -i -e "s%llvm-symbolizer%/usr/lib/llvm-16/bin/llvm-symbolizer%" .bazelrc
       - name: Setup macOS
         if: matrix.os.name == 'macOS'
-        # TODO: We want to symbolize stacks for crashes on CI. Xcode is currently based on LLVM 16
-        # but the macos-13 image has llvm@15 installed:
-        # https://github.com/actions/runner-images/blob/main/images/macos/macos-13-Readme.md
+        # TODO: We want to symbolize stacks for crashes on CI. Xcode is currently based on LLVM 17
+        # but the macos-15 image has llvm@18 installed:
+        # https://github.com/actions/runner-images/blob/main/images/macos/macos-15-Readme.md
         #
         # Not enabled because symbolication does not work on workerd macOS builds yet and running
         # llvm-symbolizer in the currently broken state causes some tests to time out on the
         # runner.
-        # Use latest available Xcode version – runner still defaults to 15.0.1.
         run: |
-          sudo xcode-select -s "/Applications/Xcode_15.1.app"
-          # export LLVM_SYMBOLIZER=$(brew --prefix llvm@15)/bin/llvm-symbolizer
+          # export LLVM_SYMBOLIZER=$(brew --prefix llvm@18)/bin/llvm-symbolizer
           # sed -i -e "s%llvm-symbolizer%${LLVM_SYMBOLIZER}%" .bazelrc
       - name: Setup Windows
         if: matrix.os.name == 'windows'