diff --git a/.github/scripts/resolve-hermes.mts b/.github/scripts/resolve-hermes.mts
new file mode 100644
index 00000000000..8d628957359
--- /dev/null
+++ b/.github/scripts/resolve-hermes.mts
@@ -0,0 +1,250 @@
+#!/usr/bin/env node
+/**
+ * CI entry point for resolving Hermes artifacts.
+ *
+ * Commands:
+ *   node resolve-hermes.mts download-hermes [Debug|Release]
+ *   node resolve-hermes.mts recompose-xcframework <tarball> <destroot>
+ *   node resolve-hermes.mts resolve-commit
+ *
+ * Each command writes results to $GITHUB_OUTPUT for use in GitHub Actions.
+ */
+import { createRequire } from 'node:module';
+import os from 'node:os';
+import { parseArgs } from 'node:util';
+import { $, echo, fs, path } from 'zx';
+
+// Use createRequire to import CommonJS modules from ESM context
+const require = createRequire(import.meta.url);
+const {
+  findMatchingHermesVersion,
+  findVersionAtMergeBase,
+  getLatestStableVersionFromNPM,
+  hermesCommitAtMergeBase,
+} = require('../../packages/react-native/scripts/ios-prebuild/microsoft-hermes.js');
+const {
+  computeNightlyTarballURL,
+} = require('../../packages/react-native/scripts/ios-prebuild/utils.js');
+
+function setActionOutput(key: string, value: string) {
+  const outputFile = process.env.GITHUB_OUTPUT;
+  if (outputFile) {
+    fs.appendFileSync(outputFile, `${key}=${value}\n`);
+  }
+}
+
+/**
+ * Downloads the upstream Hermes tarball from Maven or Sonatype.
+ *
+ * Tries multiple version resolution strategies in order:
+ * 1. Mapped version from peerDependencies (stable branches)
+ * 2. Version at merge base with facebook/react-native (main branch)
+ * 3. Latest stable version from npm (last resort)
+ *
+ * Returns {tarballPath, version} on success, or null if no tarball is available.
+ */
+async function downloadUpstreamHermesTarball(
+  buildType: string = 'Debug',
+): Promise<{ tarballPath: string; version: string } | null> {
+  const packageJsonPath = path.resolve(
+    import.meta.dirname!, '..', '..', 'packages', 'react-native', 'package.json',
+  );
+
+  // Build a list of candidate versions to try (in priority order)
+  const candidates: string[] = [];
+
+  const mapped = findMatchingHermesVersion(packageJsonPath);
+  if (mapped != null) {
+    candidates.push(mapped);
+  }
+
+  const mergeBaseVersion = findVersionAtMergeBase();
+  if (mergeBaseVersion != null && !candidates.includes(mergeBaseVersion)) {
+    candidates.push(mergeBaseVersion);
+  }
+
+  try {
+    const latestStable = await getLatestStableVersionFromNPM();
+    if (!candidates.includes(latestStable)) {
+      candidates.push(latestStable);
+    }
+  } catch {
+    // npm lookup failed, continue with what we have
+  }
+
+  if (candidates.length === 0) {
+    echo('Could not determine any upstream version to download Hermes tarball');
+    return null;
+  }
+
+  const mavenRepoUrl = 'https://repo1.maven.org/maven2';
+  const namespace = 'com/facebook/react';
+
+  for (const version of candidates) {
+    const releaseUrl = `${mavenRepoUrl}/${namespace}/react-native-artifacts/${version}/react-native-artifacts-${version}-hermes-ios-${buildType.toLowerCase()}.tar.gz`;
+    const nightlyUrl = await computeNightlyTarballURL(
+      version,
+      buildType,
+      'react-native-artifacts',
+      `hermes-ios-${buildType.toLowerCase()}.tar.gz`,
+    );
+    const urlsToTry = [releaseUrl];
+    if (nightlyUrl) {
+      urlsToTry.push(nightlyUrl);
+    }
+
+    for (const tarballUrl of urlsToTry) {
+      echo(`Trying upstream Hermes tarball (version: ${version}, ${buildType}) at ${tarballUrl}...`);
+
+      try {
+        const response = await fetch(tarballUrl);
+        if (!response.ok) {
+          echo(`Tarball not available: ${response.status} ${response.statusText}`);
+          continue;
+        }
+
+        const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'hermes-'));
+        const tarballPath = path.join(tmpDir, 'hermes-ios.tar.gz');
+        const buffer = await response.arrayBuffer();
+        fs.writeFileSync(tarballPath, Buffer.from(buffer));
+
+        echo(`Downloaded upstream Hermes tarball (${version}) to ${tarballPath}`);
+        return { tarballPath, version };
+      } catch (e: any) {
+        echo(`Error downloading tarball for ${version}: ${e.message}`);
+        continue;
+      }
+    }
+  }
+
+  echo('No upstream Hermes tarball found for any candidate version — will build from source.');
+  return null;
+}
+
+/**
+ * Extracts an upstream Hermes tarball and recomposes the xcframework to include
+ * the macOS slice, if needed.
+ *
+ * Upstream tarballs ship a universal xcframework (iOS, simulator, catalyst,
+ * tvOS, visionOS) plus a standalone macosx/hermes.framework. This function
+ * merges the standalone macOS framework into the universal xcframework using
+ * `xcodebuild -create-xcframework`.
+ *
+ * NOTE: Once upstream Hermes includes macOS in the universal xcframework
+ * natively, this function will detect the existing macOS slice and skip
+ * the recompose. At that point, this step can be removed entirely.
+ * Tracking PRs:
+ *   - https://github.com/facebook/hermes/pull/1958
+ *   - https://github.com/facebook/hermes/pull/1970
+ *   - https://github.com/facebook/hermes/pull/1971
+ */
+async function recomposeHermesXcframework(
+  tarballPath: string,
+  destroot: string,
+): Promise<boolean> {
+  // Extract tarball
+  fs.mkdirSync(destroot, { recursive: true });
+  await $`tar -xzf ${tarballPath} -C ${destroot} --strip-components=2`;
+
+  const frameworksDir = path.join(destroot, 'Library', 'Frameworks');
+  const xcfwPath = path.join(frameworksDir, 'universal', 'hermes.xcframework');
+
+  echo('Upstream tarball contents:');
+  await $`ls -la ${frameworksDir}`;
+
+  // Check if macOS is already in the universal xcframework — if so, no recompose needed
+  const xcfwContents = fs.readdirSync(xcfwPath);
+  const hasMacSlice = xcfwContents.some(
+    (entry: string) => entry.startsWith('macos') && entry.includes('arm64'),
+  );
+  if (hasMacSlice) {
+    echo('macOS slice already present in universal xcframework, skipping recompose');
+    const standaloneMacDir = path.join(frameworksDir, 'macosx');
+    if (fs.existsSync(standaloneMacDir)) {
+      fs.removeSync(standaloneMacDir);
+    }
+    return true;
+  }
+
+  // Check for standalone macOS framework
+  const standaloneMacFw = path.join(frameworksDir, 'macosx', 'hermes.framework');
+  if (!fs.existsSync(standaloneMacFw)) {
+    echo('ERROR: Upstream tarball missing macosx/hermes.framework');
+    return false;
+  }
+
+  // Collect existing frameworks from inside the universal xcframework
+  const frameworkArgs: string[] = [];
+  for (const entry of xcfwContents) {
+    const fwPath = path.join(xcfwPath, entry, 'hermes.framework');
+    if (fs.existsSync(fwPath) && fs.statSync(fwPath).isDirectory()) {
+      echo(`Found slice: ${fwPath}`);
+      frameworkArgs.push('-framework', fwPath);
+    }
+  }
+
+  // Add the standalone macOS framework
+  echo(`Found standalone macOS slice: ${standaloneMacFw}`);
+  frameworkArgs.push('-framework', standaloneMacFw);
+
+  // Build new xcframework at a temp path (frameworks reference paths inside the old xcfw)
+  const xcfwNew = path.join(frameworksDir, 'universal', 'hermes-new.xcframework');
+  const sliceCount = frameworkArgs.filter(f => f !== '-framework').length;
+  echo(`Creating new universal xcframework with ${sliceCount} slices...`);
+  await $`xcodebuild -create-xcframework ${frameworkArgs} -output ${xcfwNew} -allow-internal-distribution`;
+
+  // Swap in the recomposed xcframework
+  fs.removeSync(xcfwPath);
+  fs.renameSync(xcfwNew, xcfwPath);
+
+  // Clean up standalone macOS dir (now included in universal)
+  fs.removeSync(path.join(frameworksDir, 'macosx'));
+
+  echo('Recomposed xcframework:');
+  await $`ls -la ${xcfwPath}/`;
+
+  return true;
+}
+
+// --- CLI dispatch ---
+
+const { positionals } = parseArgs({
+  allowPositionals: true,
+  strict: false,
+});
+
+const [command, ...args] = positionals;
+
+switch (command) {
+  case 'download-hermes': {
+    const buildType = args[0] || 'Debug';
+    const result = await downloadUpstreamHermesTarball(buildType);
+    if (result != null) {
+      setActionOutput('tarball', result.tarballPath);
+      setActionOutput('version', result.version);
+      echo(`Downloaded upstream Hermes tarball for version ${result.version}`);
+    } else {
+      echo('No upstream tarball available');
+    }
+    break;
+  }
+  case 'recompose-xcframework': {
+    const [tarball, destroot] = args;
+    if (!tarball || !destroot) {
+      echo('Usage: node resolve-hermes.mts recompose-xcframework <tarball> <destroot>');
+      process.exit(1);
+    }
+    const recomposed = await recomposeHermesXcframework(tarball, destroot);
+    setActionOutput('recomposed', String(recomposed));
+    break;
+  }
+  case 'resolve-commit': {
+    const { commit } = hermesCommitAtMergeBase();
+    setActionOutput('hermes-commit', commit);
+    echo(`Resolved Hermes commit: ${commit}`);
+    break;
+  }
+  default:
+    echo(`Unknown command: ${command ?? '(none)'}. Available: download-hermes, recompose-xcframework, resolve-commit`);
+    process.exit(1);
+}
diff --git a/.github/workflows/microsoft-pr.yml b/.github/workflows/microsoft-pr.yml
index c20f2c7edfc..157cd8b05fa 100644
--- a/.github/workflows/microsoft-pr.yml
+++ b/.github/workflows/microsoft-pr.yml
@@ -132,10 +132,10 @@ jobs:
     permissions: {}
     uses: ./.github/workflows/microsoft-build-rntester.yml
 
-  build-spm:
-    name: "Build SPM"
+  prebuild-macos-core:
+    name: "Prebuild macOS Core"
     permissions: {}
-    uses: ./.github/workflows/microsoft-build-spm.yml
+    uses: ./.github/workflows/microsoft-prebuild-macos-core.yml
 
   test-react-native-macos-init:
     name: "Test react-native-macos init"
@@ -162,7 +162,7 @@ jobs:
       - yarn-constraints
       - javascript-tests
       - build-rntester
-      - build-spm
+      - prebuild-macos-core
       - test-react-native-macos-init
       # - react-native-test-app-integration
     steps:
diff --git a/.github/workflows/microsoft-prebuild-macos-core.yml b/.github/workflows/microsoft-prebuild-macos-core.yml
new file mode 100644
index 00000000000..878678e7efe
--- /dev/null
+++ b/.github/workflows/microsoft-prebuild-macos-core.yml
@@ -0,0 +1,185 @@
+name: Prebuild macOS Core
+
+on:
+  workflow_call:
+
+jobs:
+  resolve-hermes:
+    name: "Resolve Hermes"
+    uses: ./.github/workflows/microsoft-resolve-hermes.yml
+
+  build:
+    name: "Build ${{ matrix.platform }}"
+    needs: [resolve-hermes]
+    runs-on: macos-26
+    timeout-minutes: 60
+    strategy:
+      fail-fast: false
+      matrix:
+        platform: [ios, ios-simulator, macos, visionos, visionos-simulator]
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          filter: blob:none
+          fetch-depth: 0
+
+      - name: Restore slice cache
+        id: cache-slice
+        uses: actions/cache/restore@v4
+        with:
+          key: v1-macos-core-${{ matrix.platform }}-Debug-${{ hashFiles('packages/react-native/Package.swift', 'packages/react-native/scripts/ios-prebuild/*.js', 'packages/react-native/scripts/ios-prebuild.js', 'packages/react-native/React/**/*', 'packages/react-native/ReactCommon/**/*', 'packages/react-native/Libraries/**/*') }}
+          path: |
+            packages/react-native/.build/output/spm/Debug/Build/Products
+            packages/react-native/.build/headers
+
+      - name: Setup toolchain
+        if: steps.cache-slice.outputs.cache-hit != 'true'
+        uses: ./.github/actions/microsoft-setup-toolchain
+        with:
+          node-version: '22'
+          platform: ${{ matrix.platform }}
+
+      - name: Install npm dependencies
+        if: steps.cache-slice.outputs.cache-hit != 'true'
+        run: yarn install
+
+      - name: Download Hermes artifacts
+        if: steps.cache-slice.outputs.cache-hit != 'true'
+        uses: actions/download-artifact@v4
+        with:
+          name: hermes-artifacts
+          path: packages/react-native/.build/artifacts/hermes/destroot
+
+      - name: Create Hermes version marker
+        if: steps.cache-slice.outputs.cache-hit != 'true'
+        working-directory: packages/react-native
+        run: |
+          echo "prebuilt-Debug" > .build/artifacts/hermes/version.txt
+
+      - name: Setup workspace (using prebuilt Hermes)
+        if: steps.cache-slice.outputs.cache-hit != 'true'
+        working-directory: packages/react-native
+        env:
+          HERMES_VERSION: prebuilt
+        run: node scripts/ios-prebuild.js -s -f Debug
+
+      - name: Build (${{ matrix.platform }})
+        if: steps.cache-slice.outputs.cache-hit != 'true'
+        working-directory: packages/react-native
+        run: node scripts/ios-prebuild.js -b -f Debug -p ${{ matrix.platform }}
+
+      - name: Save slice cache
+        if: ${{ github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/heads/') && endsWith(github.ref, '-stable') }}
+        uses: actions/cache/save@v4
+        with:
+          key: v1-macos-core-${{ matrix.platform }}-Debug-${{ hashFiles('packages/react-native/Package.swift', 'packages/react-native/scripts/ios-prebuild/*.js', 'packages/react-native/scripts/ios-prebuild.js', 'packages/react-native/React/**/*', 'packages/react-native/ReactCommon/**/*', 'packages/react-native/Libraries/**/*') }}
+          path: |
+            packages/react-native/.build/output/spm/Debug/Build/Products
+            packages/react-native/.build/headers
+
+      - name: Upload headers
+        uses: actions/upload-artifact@v4
+        with:
+          name: prebuild-macos-core-headers-Debug-${{ matrix.platform }}
+          path: packages/react-native/.build/headers
+
+      - name: Upload slice artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: prebuild-macos-core-slice-Debug-${{ matrix.platform }}
+          path: packages/react-native/.build/output/spm/Debug/Build/Products
+
+  compose-xcframework:
+    name: "Compose XCFramework (Debug)"
+    needs: [build]
+    if: ${{ always() && !cancelled() && !failure() }}
+    runs-on: macos-26
+    timeout-minutes: 30
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          filter: blob:none
+
+      - name: Restore compose cache
+        id: cache-xcframework
+        uses: actions/cache/restore@v4
+        with:
+          key: v1-macos-core-xcframework-Debug-${{ hashFiles('packages/react-native/Package.swift', 'packages/react-native/scripts/ios-prebuild/*.js', 'packages/react-native/scripts/ios-prebuild.js', 'packages/react-native/React/**/*', 'packages/react-native/ReactCommon/**/*', 'packages/react-native/Libraries/**/*') }}
+          path: |
+            packages/react-native/.build/output/xcframeworks/ReactCoreDebug.xcframework.tar.gz
+            packages/react-native/.build/output/xcframeworks/ReactCoreDebug.framework.dSYM.tar.gz
+
+      - name: Setup toolchain
+        if: steps.cache-xcframework.outputs.cache-hit != 'true'
+        uses: ./.github/actions/microsoft-setup-toolchain
+        with:
+          node-version: '22'
+          platform: ios
+
+      - name: Install npm dependencies
+        if: steps.cache-xcframework.outputs.cache-hit != 'true'
+        run: yarn install
+
+      - name: Download slice artifacts
+        if: steps.cache-xcframework.outputs.cache-hit != 'true'
+        uses: actions/download-artifact@v4
+        with:
+          pattern: prebuild-macos-core-slice-Debug-*
+          path: packages/react-native/.build/output/spm/Debug/Build/Products
+          merge-multiple: true
+
+      - name: Download headers
+        if: steps.cache-xcframework.outputs.cache-hit != 'true'
+        uses: actions/download-artifact@v4
+        with:
+          pattern: prebuild-macos-core-headers-Debug-*
+          path: packages/react-native/.build/headers
+          merge-multiple: true
+
+      - name: Verify downloaded artifacts
+        if: steps.cache-xcframework.outputs.cache-hit != 'true'
+        run: |
+          echo "=== Products directory ==="
+          ls -R packages/react-native/.build/output/spm/Debug/Build/Products/ | head -40
+          echo "=== Headers directory ==="
+          ls packages/react-native/.build/headers/ | head -20
+
+      - name: Create XCFramework
+        if: steps.cache-xcframework.outputs.cache-hit != 'true'
+        working-directory: packages/react-native
+        run: node scripts/ios-prebuild -c -f Debug
+
+      - name: Compress XCFramework
+        if: steps.cache-xcframework.outputs.cache-hit != 'true'
+        run: |
+          cd packages/react-native/.build/output/xcframeworks/Debug
+          tar -cz -f ../ReactCoreDebug.xcframework.tar.gz React.xcframework
+
+      - name: Compress dSYMs
+        if: steps.cache-xcframework.outputs.cache-hit != 'true'
+        run: |
+          cd packages/react-native/.build/output/xcframeworks/Debug/Symbols
+          tar -cz -f ../../ReactCoreDebug.framework.dSYM.tar.gz .
+
+      - name: Save compose cache
+        if: ${{ github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/heads/') && endsWith(github.ref, '-stable') }}
+        uses: actions/cache/save@v4
+        with:
+          key: v1-macos-core-xcframework-Debug-${{ hashFiles('packages/react-native/Package.swift', 'packages/react-native/scripts/ios-prebuild/*.js', 'packages/react-native/scripts/ios-prebuild.js', 'packages/react-native/React/**/*', 'packages/react-native/ReactCommon/**/*', 'packages/react-native/Libraries/**/*') }}
+          path: |
+            packages/react-native/.build/output/xcframeworks/ReactCoreDebug.xcframework.tar.gz
+            packages/react-native/.build/output/xcframeworks/ReactCoreDebug.framework.dSYM.tar.gz
+
+      - name: Upload XCFramework
+        uses: actions/upload-artifact@v4
+        with:
+          name: ReactCoreDebug.xcframework.tar.gz
+          path: packages/react-native/.build/output/xcframeworks/ReactCoreDebug.xcframework.tar.gz
+          retention-days: 14
+
+      - name: Upload dSYMs
+        uses: actions/upload-artifact@v4
+        with:
+          name: ReactCoreDebug.framework.dSYM.tar.gz
+          path: packages/react-native/.build/output/xcframeworks/ReactCoreDebug.framework.dSYM.tar.gz
+          retention-days: 14
diff --git a/.github/workflows/microsoft-build-spm.yml b/.github/workflows/microsoft-resolve-hermes.yml
similarity index 60%
rename from .github/workflows/microsoft-build-spm.yml
rename to .github/workflows/microsoft-resolve-hermes.yml
index ae9752c507f..78f590715dd 100644
--- a/.github/workflows/microsoft-build-spm.yml
+++ b/.github/workflows/microsoft-resolve-hermes.yml
@@ -1,44 +1,81 @@
-name: Build SwiftPM
+# Resolve Hermes — reusable workflow called by microsoft-prebuild-macos-core.yml
+#
+# Strategy (fast path first):
+#   1. Download upstream Hermes tarball from Maven/Sonatype
+#   2. If found → recompose xcframework (add macOS slice) → upload artifact → done
+#   3. If not found → resolve Hermes commit at merge base → check cache → upload if cached
+#
+# Build-from-source fallback (only when recomposed != true AND cache-hit != true):
+#   build-hermesc → build 5 platform slices in parallel → assemble universal xcframework
+#
+name: Resolve Hermes
 
 on:
   workflow_call:
 
 jobs:
+  # ---------------------------------------------------------------------------
+  # Fast path: download upstream tarball and recompose, or resolve commit + cache
+  # ---------------------------------------------------------------------------
   resolve-hermes:
     name: "Resolve Hermes"
     runs-on: macos-15
-    timeout-minutes: 10
+    timeout-minutes: 15
     outputs:
       hermes-commit: ${{ steps.resolve.outputs.hermes-commit }}
       cache-hit: ${{ steps.cache.outputs.cache-hit }}
+      recomposed: ${{ steps.recompose.outputs.recomposed }}
     steps:
       - uses: actions/checkout@v4
         with:
           filter: blob:none
           fetch-depth: 0
 
-      - name: Setup Xcode
-        run: sudo xcode-select --switch /Applications/Xcode_16.2.app
-
-      - name: Set up Node.js
-        uses: actions/setup-node@v4.4.0
+      - name: Setup toolchain
+        uses: ./.github/actions/microsoft-setup-toolchain
         with:
           node-version: '22'
-          cache: yarn
-          registry-url: https://registry.npmjs.org
+          platform: macos
 
       - name: Install npm dependencies
         run: yarn install
 
+      # Step 1: Try to download a prebuilt Hermes tarball from upstream Maven/Sonatype.
+      # Writes tarball= and version= to $GITHUB_OUTPUT if successful.
+      - name: Download upstream Hermes tarball
+        id: download
+        run: node .github/scripts/resolve-hermes.mts download-hermes Debug
+
+      # Step 2: If tarball found, recompose the xcframework to include the macOS slice
+      # (or skip if macOS is already present in the universal xcframework).
+      # Writes recomposed=true/false to $GITHUB_OUTPUT.
+      - name: Recompose xcframework with macOS slice
+        id: recompose
+        if: steps.download.outputs.tarball != ''
+        run: >-
+          node .github/scripts/resolve-hermes.mts
+          recompose-xcframework
+          "${{ steps.download.outputs.tarball }}"
+          "${{ github.workspace }}/hermes-destroot"
+
+      # Upload recomposed artifacts — the prebuild-macos-core workflow downloads these
+      - name: Upload recomposed Hermes artifacts
+        if: steps.recompose.outputs.recomposed == 'true'
+        uses: actions/upload-artifact@v4
+        with:
+          name: hermes-artifacts
+          path: hermes-destroot
+          retention-days: 30
+
+      # Step 3 (fallback): No upstream tarball — resolve the Hermes commit hash
+      # at the merge base with facebook/react-native and check the build cache.
       - name: Resolve Hermes commit at merge base
+        if: steps.recompose.outputs.recomposed != 'true'
         id: resolve
-        working-directory: packages/react-native
-        run: |
-          COMMIT=$(node -e "const {hermesCommitAtMergeBase} = require('./scripts/ios-prebuild/macosVersionResolver'); console.log(hermesCommitAtMergeBase().commit);" 2>&1 | grep -E '^[0-9a-f]{40}$')
-          echo "hermes-commit=$COMMIT" >> "$GITHUB_OUTPUT"
-          echo "Resolved Hermes commit: $COMMIT"
+        run: node .github/scripts/resolve-hermes.mts resolve-commit
 
       - name: Restore Hermes cache
+        if: steps.recompose.outputs.recomposed != 'true'
         id: cache
         uses: actions/cache/restore@v4
         with:
@@ -46,16 +83,20 @@ jobs:
           path: hermes-destroot
 
       - name: Upload cached Hermes artifacts
-        if: steps.cache.outputs.cache-hit == 'true'
+        if: steps.recompose.outputs.recomposed != 'true' && steps.cache.outputs.cache-hit == 'true'
         uses: actions/upload-artifact@v4
         with:
           name: hermes-artifacts
           path: hermes-destroot
           retention-days: 30
 
+  # ---------------------------------------------------------------------------
+  # Build-from-source fallback — only runs when no recomposed or cached artifact
+  # Pipeline: hermesc (host compiler) → 5 platform slices → assemble xcframework
+  # ---------------------------------------------------------------------------
   build-hermesc:
     name: "Build hermesc"
-    if: ${{ needs.resolve-hermes.outputs.cache-hit != 'true' }}
+    if: ${{ needs.resolve-hermes.outputs.recomposed != 'true' && needs.resolve-hermes.outputs.cache-hit != 'true' }}
     needs: resolve-hermes
     runs-on: macos-15
     timeout-minutes: 30
@@ -64,8 +105,11 @@ jobs:
         with:
           filter: blob:none
 
-      - name: Setup Xcode
-        run: sudo xcode-select --switch /Applications/Xcode_16.2.app
+      - name: Setup toolchain
+        uses: ./.github/actions/microsoft-setup-toolchain
+        with:
+          platform: macos
+          cache-npm-dependencies: ''
 
       - name: Clone Hermes
         uses: actions/checkout@v4
@@ -93,7 +137,7 @@ jobs:
 
   build-hermes-slice:
     name: "Hermes ${{ matrix.slice }}"
-    if: ${{ needs.resolve-hermes.outputs.cache-hit != 'true' }}
+    if: ${{ needs.resolve-hermes.outputs.recomposed != 'true' && needs.resolve-hermes.outputs.cache-hit != 'true' }}
     needs: [resolve-hermes, build-hermesc]
     runs-on: macos-15
     timeout-minutes: 45
@@ -101,21 +145,27 @@ jobs:
       fail-fast: false
       matrix:
         slice: [iphoneos, iphonesimulator, macosx, xros, xrsimulator]
+        include:
+          - slice: iphoneos
+            platform: ios
+          - slice: iphonesimulator
+            platform: ios
+          - slice: macosx
+            platform: macos
+          - slice: xros
+            platform: visionos
+          - slice: xrsimulator
+            platform: visionos
     steps:
       - uses: actions/checkout@v4
         with:
           filter: blob:none
 
-      - name: Setup Xcode
-        run: sudo xcode-select --switch /Applications/Xcode_16.2.app
-
-      - name: Download visionOS SDK
-        if: ${{ matrix.slice == 'xros' || matrix.slice == 'xrsimulator' }}
-        run: |
-          sudo xcodebuild -runFirstLaunch
-          sudo xcrun simctl list
-          sudo xcodebuild -downloadPlatform visionOS
-          sudo xcodebuild -runFirstLaunch
+      - name: Setup toolchain
+        uses: ./.github/actions/microsoft-setup-toolchain
+        with:
+          platform: ${{ matrix.platform }}
+          cache-npm-dependencies: ''
 
       - name: Clone Hermes
         uses: actions/checkout@v4
@@ -155,7 +205,7 @@ jobs:
 
   assemble-hermes:
     name: "Assemble Hermes xcframework"
-    if: ${{ needs.resolve-hermes.outputs.cache-hit != 'true' }}
+    if: ${{ needs.resolve-hermes.outputs.recomposed != 'true' && needs.resolve-hermes.outputs.cache-hit != 'true' }}
     needs: [resolve-hermes, build-hermes-slice]
     runs-on: macos-15
     timeout-minutes: 15
@@ -208,50 +258,3 @@ jobs:
           name: hermes-artifacts
           path: hermes/destroot
           retention-days: 30
-
-  build-spm:
-    name: "SPM ${{ matrix.platform }}"
-    needs: [resolve-hermes, assemble-hermes]
-    # Run when upstream jobs succeeded or were skipped (cache hit)
-    if: ${{ always() && !cancelled() && !failure() }}
-    runs-on: macos-26
-    timeout-minutes: 60
-    strategy:
-      fail-fast: false
-      matrix:
-        platform: [ios, macos, visionos]
-    steps:
-      - uses: actions/checkout@v4
-        with:
-          filter: blob:none
-          fetch-depth: 0
-
-      - name: Setup toolchain
-        uses: ./.github/actions/microsoft-setup-toolchain
-        with:
-          node-version: '22'
-          platform: ${{ matrix.platform }}
-
-      - name: Install npm dependencies
-        run: yarn install
-
-      - name: Download Hermes artifacts
-        uses: actions/download-artifact@v4
-        with:
-          name: hermes-artifacts
-          path: packages/react-native/.build/artifacts/hermes/destroot
-
-      - name: Create Hermes version marker
-        working-directory: packages/react-native
-        run: |
-          echo "prebuilt-Debug" > .build/artifacts/hermes/version.txt
-
-      - name: Setup SPM workspace (using prebuilt Hermes)
-        working-directory: packages/react-native
-        env:
-          HERMES_VERSION: prebuilt
-        run: node scripts/ios-prebuild.js -s -f Debug
-
-      - name: Build SPM (${{ matrix.platform }})
-        working-directory: packages/react-native
-        run: node scripts/ios-prebuild.js -b -f Debug -p ${{ matrix.platform }}
diff --git a/package.json b/package.json
index d57a41c95ab..f262e9fe2a5 100644
--- a/package.json
+++ b/package.json
@@ -114,7 +114,8 @@
     "temp-dir": "^2.0.0",
     "tinybench": "^3.1.0",
     "typescript": "5.8.3",
-    "ws": "^6.2.3"
+    "ws": "^6.2.3",
+    "zx": "^8.2.4"
   },
   "resolutions": {
     "@grpc/proto-loader": "^0.7.8",
diff --git a/packages/react-native/scripts/ios-prebuild/cli.js b/packages/react-native/scripts/ios-prebuild/cli.js
index c2f3586f46f..e18e663df0a 100644
--- a/packages/react-native/scripts/ios-prebuild/cli.js
+++ b/packages/react-native/scripts/ios-prebuild/cli.js
@@ -20,6 +20,7 @@ const platforms /*: $ReadOnlyArray<Platform> */ = [
   'mac-catalyst',
   'macos', // [macOS]
   'visionos', // [macOS]
+  'visionos-simulator', // [macOS]
 ];
 
 // CI can't use commas in cache keys, so 'macOS,variant=Mac Catalyst' was creating troubles
@@ -30,6 +31,7 @@ const platformToDestination /*: $ReadOnly<{|[Platform]: Destination|}> */ = {
   'mac-catalyst': 'macOS,variant=Mac Catalyst',
   macos: 'macOS', // [macOS]
   visionos: 'visionOS', // [macOS]
+  'visionos-simulator': 'visionOS Simulator', // [macOS]
 };
 
 const cli = yargs
diff --git a/packages/react-native/scripts/ios-prebuild/hermes.js b/packages/react-native/scripts/ios-prebuild/hermes.js
index 4b997cb4a90..92cc5b5eda6 100644
--- a/packages/react-native/scripts/ios-prebuild/hermes.js
+++ b/packages/react-native/scripts/ios-prebuild/hermes.js
@@ -11,7 +11,7 @@
 const {
   findMatchingHermesVersion,
   hermesCommitAtMergeBase,
-} = require('./macosVersionResolver'); // [macOS]
+} = require('./microsoft-hermes'); // [macOS]
 const {computeNightlyTarballURL, createLogger} = require('./utils');
 const {execSync} = require('child_process');
 const fs = require('fs');
diff --git a/packages/react-native/scripts/ios-prebuild/macosVersionResolver.js b/packages/react-native/scripts/ios-prebuild/microsoft-hermes.js
similarity index 95%
rename from packages/react-native/scripts/ios-prebuild/macosVersionResolver.js
rename to packages/react-native/scripts/ios-prebuild/microsoft-hermes.js
index 70b85d3cebe..9bdeec72d8f 100644
--- a/packages/react-native/scripts/ios-prebuild/macosVersionResolver.js
+++ b/packages/react-native/scripts/ios-prebuild/microsoft-hermes.js
@@ -4,7 +4,11 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * [macOS] Handles version resolution for macOS fork branches.
+ * [macOS] Resolves Hermes artifacts for macOS fork branches.
+ *
+ * Library functions for version resolution and resolving Hermes commits.
+ * The CI entry point that orchestrates downloading, recomposing, and
+ * caching is at .github/scripts/resolve-hermes.mts.
  *
  * @flow
  * @format
diff --git a/packages/react-native/scripts/ios-prebuild/reactNativeDependencies.js b/packages/react-native/scripts/ios-prebuild/reactNativeDependencies.js
index cc0bc9f8ff1..b4efe4fdea1 100644
--- a/packages/react-native/scripts/ios-prebuild/reactNativeDependencies.js
+++ b/packages/react-native/scripts/ios-prebuild/reactNativeDependencies.js
@@ -14,7 +14,7 @@ const {
   findMatchingHermesVersion,
   findVersionAtMergeBase,
   getLatestStableVersionFromNPM,
-} = require('./macosVersionResolver'); // [macOS]
+} = require('./microsoft-hermes'); // [macOS]
 const {computeNightlyTarballURL, createLogger} = require('./utils');
 const {execSync} = require('child_process');
 const fs = require('fs');
diff --git a/packages/react-native/scripts/ios-prebuild/types.js b/packages/react-native/scripts/ios-prebuild/types.js
index 87f516c5ba9..cdb554815a6 100644
--- a/packages/react-native/scripts/ios-prebuild/types.js
+++ b/packages/react-native/scripts/ios-prebuild/types.js
@@ -13,15 +13,17 @@ export type Platform =
   'ios' |
   'ios-simulator' |
   'mac-catalyst' |
-  'macos' |        // [macOS]
-  'visionos';      // [macOS]
+  'macos' |              // [macOS]
+  'visionos' |           // [macOS]
+  'visionos-simulator';  // [macOS]
 
 export type Destination =
   'iOS' |
   'iOS Simulator' |
   'macOS,variant=Mac Catalyst' |
-  'macOS' |        // [macOS]
-  'visionOS';      // [macOS]
+  'macOS' |              // [macOS]
+  'visionOS' |           // [macOS]
+  'visionOS Simulator';  // [macOS]
 
 export type BuildFlavor = 'Debug' | 'Release';
 */
diff --git a/yarn.lock b/yarn.lock
index 6df6b951b68..0fe1ab5a0f8 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2963,6 +2963,7 @@ __metadata:
     tinybench: "npm:^3.1.0"
     typescript: "npm:5.8.3"
     ws: "npm:^6.2.3"
+    zx: "npm:^8.2.4"
   languageName: unknown
   linkType: soft
 
@@ -14214,3 +14215,12 @@ __metadata:
   checksum: 10c0/5718ec35e3c40b600316c5b4c5e4976f7fee68151bc8f8d90ec18a469be9571f072e1bbaace10f1e85cf8892ea12d90821b200e980ab46916a6166a4260a983c
   languageName: node
   linkType: hard
+
+"zx@npm:^8.2.4":
+  version: 8.8.5
+  resolution: "zx@npm:8.8.5"
+  bin:
+    zx: build/cli.js
+  checksum: 10c0/1273e4f72cfe35a59041aef5a56fd87318bc4e11947d101810b67e5c486ab30574042938728e8a15e085de985e762b8585fcdaab4cf87fd113153b63a5846611
+  languageName: node
+  linkType: hard