diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8e9bce0..b396526 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -14,7 +14,11 @@ jobs:
   build:
     name: ${{ matrix.config.variant }} ${{ matrix.config.target }} ${{ matrix.config.v8_enable_pointer_compression && 'ptrcomp' || '' }} ${{ matrix.config.v8_enable_multi_cage && 'multicage' || '' }}
     runs-on: ${{ matrix.config.os }}
-    timeout-minutes: 180
+    # Standard runners have fewer cores than the larger runners this matrix
+    # used to run on, so a cold-cache build takes considerably longer: the
+    # debug riscv64 cross build no longer fits in 180 minutes, and the debug
+    # aarch64 one only just did. 360 is the ceiling GitHub allows.
+    timeout-minutes: 360
     strategy:
       # Always run main branch builds to completion. This allows the cache to
       # stay mostly up-to-date in situations where a single job fails due to
@@ -27,25 +31,25 @@ jobs:
         !contains(github.event.pull_request.labels.*.name, 'no-fail-fast') }}
       matrix:
         config:
-          - os: macos-15-large
+          - os: macos-15
             target: x86_64-apple-darwin
             variant: debug
             v8_enable_pointer_compression: false
             cargo: cargo
 
-          - os: macos-15-large
+          - os: macos-15
             target: x86_64-apple-darwin
             variant: release
             v8_enable_pointer_compression: false
             cargo: cargo
 
-          - os: macos-15-large
+          - os: macos-15
             target: x86_64-apple-darwin
             variant: debug
             v8_enable_pointer_compression: true
             cargo: cargo
 
-          - os: macos-15-large
+          - os: macos-15
             target: x86_64-apple-darwin
             variant: release
             v8_enable_pointer_compression: true
@@ -91,25 +95,25 @@ jobs:
             v8_enable_pointer_compression: false
             cargo: cargo
 
-          - os: ${{ github.repository == 'denoland/rusty_v8' && 'ubuntu-22.04-xl' || 'ubuntu-22.04' }}
+          - os: ubuntu-22.04
             target: x86_64-unknown-linux-gnu
             variant: debug
             v8_enable_pointer_compression: false
             cargo: cargo
 
-          - os: ${{ github.repository == 'denoland/rusty_v8' && 'ubuntu-22.04-xl' || 'ubuntu-22.04' }}
+          - os: ubuntu-22.04
             target: x86_64-unknown-linux-gnu
             variant: release
             v8_enable_pointer_compression: false
             cargo: cargo
 
-          - os: ${{ github.repository == 'denoland/rusty_v8' && 'ubuntu-22.04-xl' || 'ubuntu-22.04' }}
+          - os: ubuntu-22.04
             target: x86_64-unknown-linux-gnu
             variant: debug
             v8_enable_pointer_compression: true
             cargo: cargo
 
-          - os: ${{ github.repository == 'denoland/rusty_v8' && 'ubuntu-22.04-xl' || 'ubuntu-22.04' }}
+          - os: ubuntu-22.04
             target: x86_64-unknown-linux-gnu
             variant: release
             v8_enable_pointer_compression: true
@@ -119,7 +123,7 @@ jobs:
           # `v8::IsolateGroup::create()` works. Built and tested here so the
           # isolate group code stays honest, but deliberately not published:
           # embedders that want it build this crate from source.
-          - os: ${{ github.repository == 'denoland/rusty_v8' && 'ubuntu-22.04-xl' || 'ubuntu-22.04' }}
+          - os: ubuntu-22.04
             target: x86_64-unknown-linux-gnu
             variant: release
             v8_enable_pointer_compression: true
@@ -131,7 +135,7 @@ jobs:
           # Release only for now, like the iOS targets: V8's debug-only
           # execinfo backtrace path (external-reference-table.cc) assumes glibc
           # and doesn't compile against musl.
-          - os: ${{ github.repository == 'denoland/rusty_v8' && 'ubuntu-22.04-xl' || 'ubuntu-22.04' }}
+          - os: ubuntu-22.04
             target: x86_64-unknown-linux-musl
             variant: release
             v8_enable_pointer_compression: false
@@ -140,7 +144,7 @@ jobs:
 
           # aarch64 musl: cross-compiled on the x64 glibc runner (host + snapshot
           # toolchains stay glibc; only the arm64 target objects are musl).
-          - os: ${{ github.repository == 'denoland/rusty_v8' && 'ubuntu-22.04-xl' || 'ubuntu-22.04' }}
+          - os: ubuntu-22.04
             target: aarch64-unknown-linux-musl
             variant: release
             v8_enable_pointer_compression: false
@@ -153,25 +157,25 @@ jobs:
             v8_enable_pointer_compression: false
             cargo: cargo
 
-          - os: ${{ github.repository == 'denoland/rusty_v8' && 'ubuntu-22.04-xl' || 'ubuntu-22.04' }}
+          - os: ubuntu-22.04
             target: aarch64-unknown-linux-gnu
             variant: debug
             v8_enable_pointer_compression: false
             cargo: cargo
 
-          - os: ${{ github.repository == 'denoland/rusty_v8' && 'ubuntu-22.04-xl' || 'ubuntu-22.04' }}
+          - os: ubuntu-22.04
             target: aarch64-unknown-linux-gnu
             variant: release
             v8_enable_pointer_compression: false
             cargo: cargo
 
-          - os: ${{ github.repository == 'denoland/rusty_v8' && 'ubuntu-22.04-xl' || 'ubuntu-22.04' }}
+          - os: ubuntu-22.04
             target: riscv64gc-unknown-linux-gnu
             variant: debug
             v8_enable_pointer_compression: false
             cargo: cargo
 
-          - os: ${{ github.repository == 'denoland/rusty_v8' && 'ubuntu-22.04-xl' || 'ubuntu-22.04' }}
+          - os: ubuntu-22.04
             target: riscv64gc-unknown-linux-gnu
             variant: release
             v8_enable_pointer_compression: false
@@ -270,6 +274,16 @@ jobs:
         if: contains(matrix.config.target, 'ios')
         run: rustup target add ${{ matrix.config.target }}
 
+      # x86_64 macOS is cross-compiled on the free arm64 macOS runner (the
+      # x86_64 "large" runner is billed even on public repos). Unlike the iOS
+      # and musl cross builds, the test suite still runs here: the x86_64 test
+      # binaries execute under Rosetta 2.
+      - name: Install x86_64 macOS target and Rosetta 2
+        if: matrix.config.target == 'x86_64-apple-darwin'
+        run: |
+          rustup target add x86_64-apple-darwin
+          softwareupdate --install-rosetta --agree-to-license
+
       - name: Install musl cross compilation toolchain
         if: contains(matrix.config.target, '-linux-musl')
         run: |
@@ -346,7 +360,9 @@ jobs:
         run: |
           $version = "v0.8.2"
           $platform =
-            @{ "x86_64-apple-darwin"       = "x86_64-apple-darwin"
+            @{ # x86_64 macOS cross-compiles on the arm64 macOS runner, so use
+               # the host sccache binary.
+               "x86_64-apple-darwin"       = "aarch64-apple-darwin"
                "aarch64-apple-darwin"      = "aarch64-apple-darwin"
                "x86_64-unknown-linux-gnu"  = "x86_64-unknown-linux-musl"
                "x86_64-unknown-linux-musl" = "x86_64-unknown-linux-musl"
@@ -682,7 +698,7 @@ jobs:
 
   publish:
     needs: [build, build-windows-arm64]
-    runs-on: ${{ github.repository == 'denoland/rusty_v8' && 'ubuntu-22.04-xl' || 'ubuntu-22.04' }}
+    runs-on: ubuntu-22.04
     if: github.repository == 'denoland/rusty_v8' && startsWith(github.ref, 'refs/tags/')
     steps:
       - name: Configure git
diff --git a/build.rs b/build.rs
index e2c6baa..15d31eb 100644
--- a/build.rs
+++ b/build.rs
@@ -520,6 +520,14 @@ fn build_v8(is_asan: bool) {
       maybe_install_sysroot("amd64");
     }
   }
+  // Without this, GN defaults target_cpu to host_cpu, which the Apple Silicon
+  // block above pins to "arm64". An x86_64 macOS build hosted on arm64 (as CI
+  // does, to stay on the free standard runner) would then silently produce an
+  // arm64 V8 for an x86_64 Rust target. On an x86_64 host this matches GN's
+  // own default and is a no-op.
+  if target_arch == "x86_64" {
+    gn_args.push(r#"target_cpu="x64""#.to_string());
+  }
   if target_arch == "arm" {
     gn_args.push(r#"target_cpu="arm""#.to_string());
     gn_args.push(r#"v8_target_cpu="arm""#.to_string());