diff --git a/.github/workflows/microsoft-build-spm.yml b/.github/workflows/microsoft-build-spm.yml
new file mode 100644
index 000000000000..46a6c25a62c8
--- /dev/null
+++ b/.github/workflows/microsoft-build-spm.yml
@@ -0,0 +1,256 @@
+name: Build SwiftPM
+
+on:
+  workflow_call:
+
+jobs:
+  resolve-hermes:
+    name: "Resolve Hermes"
+    runs-on: macos-15
+    timeout-minutes: 10
+    outputs:
+      hermes-commit: ${{ steps.resolve.outputs.hermes-commit }}
+      cache-hit: ${{ steps.cache.outputs.cache-hit }}
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          filter: blob:none
+          fetch-depth: 0
+
+      - name: Setup Xcode
+        run: sudo xcode-select --switch /Applications/Xcode_16.2.app
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4.4.0
+        with:
+          node-version: '22'
+          cache: yarn
+          registry-url: https://registry.npmjs.org
+
+      - name: Install npm dependencies
+        run: yarn install
+
+      - name: Resolve Hermes commit at merge base
+        id: resolve
+        working-directory: packages/react-native
+        run: |
+          COMMIT=$(node -e "const {hermesCommitAtMergeBase} = require('./scripts/ios-prebuild/hermes'); console.log(hermesCommitAtMergeBase().commit);" 2>&1 | grep -E '^[0-9a-f]{40}$')
+          echo "hermes-commit=$COMMIT" >> "$GITHUB_OUTPUT"
+          echo "Resolved Hermes commit: $COMMIT"
+
+      - name: Restore Hermes cache
+        id: cache
+        uses: actions/cache/restore@v4
+        with:
+          key: hermes-v1-${{ steps.resolve.outputs.hermes-commit }}-Debug
+          path: hermes-destroot
+
+      - name: Upload cached Hermes artifacts
+        if: steps.cache.outputs.cache-hit == 'true'
+        uses: actions/upload-artifact@v4
+        with:
+          name: hermes-artifacts
+          path: hermes-destroot
+          retention-days: 1
+
+  build-hermesc:
+    name: "Build hermesc"
+    if: ${{ needs.resolve-hermes.outputs.cache-hit != 'true' }}
+    needs: resolve-hermes
+    runs-on: macos-15
+    timeout-minutes: 30
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          filter: blob:none
+
+      - name: Setup Xcode
+        run: sudo xcode-select --switch /Applications/Xcode_16.2.app
+
+      - name: Clone Hermes
+        uses: actions/checkout@v4
+        with:
+          repository: facebook/hermes
+          ref: ${{ needs.resolve-hermes.outputs.hermes-commit }}
+          path: hermes
+
+      - name: Build hermesc
+        working-directory: hermes
+        env:
+          HERMES_PATH: ${{ github.workspace }}/hermes
+          JSI_PATH: ${{ github.workspace }}/hermes/API/jsi
+          MAC_DEPLOYMENT_TARGET: '14.0'
+        run: |
+          source $GITHUB_WORKSPACE/packages/react-native/sdks/hermes-engine/utils/build-apple-framework.sh
+          build_host_hermesc
+
+      - name: Upload hermesc artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: hermesc
+          path: hermes/build_host_hermesc
+          retention-days: 1
+
+  build-hermes-slice:
+    name: "Hermes ${{ matrix.slice }}"
+    if: ${{ needs.resolve-hermes.outputs.cache-hit != 'true' }}
+    needs: [resolve-hermes, build-hermesc]
+    runs-on: macos-15
+    timeout-minutes: 45
+    strategy:
+      fail-fast: false
+      matrix:
+        slice: [iphoneos, iphonesimulator, macosx, xros, xrsimulator]
+    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: Clone Hermes
+        uses: actions/checkout@v4
+        with:
+          repository: facebook/hermes
+          ref: ${{ needs.resolve-hermes.outputs.hermes-commit }}
+          path: hermes
+
+      - name: Download hermesc
+        uses: actions/download-artifact@v4
+        with:
+          name: hermesc
+          path: hermes/build_host_hermesc
+
+      - name: Restore hermesc permissions
+        run: chmod +x ${{ github.workspace }}/hermes/build_host_hermesc/bin/hermesc
+
+      - name: Build Hermes slice (${{ matrix.slice }})
+        working-directory: hermes
+        env:
+          BUILD_TYPE: Debug
+          HERMES_PATH: ${{ github.workspace }}/hermes
+          JSI_PATH: ${{ github.workspace }}/hermes/API/jsi
+          IOS_DEPLOYMENT_TARGET: '15.1'
+          MAC_DEPLOYMENT_TARGET: '14.0'
+          XROS_DEPLOYMENT_TARGET: '1.0'
+          RELEASE_VERSION: '1000.0.0'
+        run: |
+          bash $GITHUB_WORKSPACE/packages/react-native/sdks/hermes-engine/utils/build-ios-framework.sh "${{ matrix.slice }}"
+
+      - name: Upload slice artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: hermes-slice-${{ matrix.slice }}
+          path: hermes/destroot
+          retention-days: 1
+
+  assemble-hermes:
+    name: "Assemble Hermes xcframework"
+    if: ${{ needs.resolve-hermes.outputs.cache-hit != 'true' }}
+    needs: [resolve-hermes, build-hermes-slice]
+    runs-on: macos-15
+    timeout-minutes: 15
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          filter: blob:none
+
+      - name: Download all slice artifacts
+        uses: actions/download-artifact@v4
+        with:
+          pattern: hermes-slice-*
+          path: /tmp/slices
+
+      - name: Assemble destroot from slices
+        run: |
+          mkdir -p ${{ github.workspace }}/hermes/destroot/Library/Frameworks
+          for slice_dir in /tmp/slices/hermes-slice-*; do
+            slice_name=$(basename "$slice_dir" | sed 's/hermes-slice-//')
+            echo "Copying slice: $slice_name"
+            cp -R "$slice_dir/Library/Frameworks/$slice_name" ${{ github.workspace }}/hermes/destroot/Library/Frameworks/
+            # Copy include and bin directories (identical across slices, only need one copy)
+            if [ -d "$slice_dir/include" ] && [ ! -d ${{ github.workspace }}/hermes/destroot/include ]; then
+              cp -R "$slice_dir/include" ${{ github.workspace }}/hermes/destroot/
+            fi
+            if [ -d "$slice_dir/bin" ]; then
+              cp -R "$slice_dir/bin" ${{ github.workspace }}/hermes/destroot/
+            fi
+          done
+          echo "Assembled destroot contents:"
+          ls -la ${{ github.workspace }}/hermes/destroot/Library/Frameworks/
+
+      - name: Create universal xcframework
+        working-directory: hermes
+        env:
+          HERMES_PATH: ${{ github.workspace }}/hermes
+        run: |
+          source $GITHUB_WORKSPACE/packages/react-native/sdks/hermes-engine/utils/build-apple-framework.sh
+          create_universal_framework "iphoneos" "iphonesimulator" "macosx" "xros" "xrsimulator"
+
+      - name: Save Hermes cache
+        uses: actions/cache/save@v4
+        with:
+          key: hermes-v1-${{ needs.resolve-hermes.outputs.hermes-commit }}-Debug
+          path: hermes/destroot
+
+      - name: Upload Hermes artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: hermes-artifacts
+          path: hermes/destroot
+          retention-days: 1
+
+  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: ${{ matrix.platform }}
+
+      - name: Install npm dependencies
+        run: yarn install
+
+      - name: Download Hermes artifacts
+        uses: actions/download-artifact@v4
+        with:
+          name: hermes-artifacts
+          path: packages/react-native/.build/artifacts/hermes/destroot
+
+      - name: Create Hermes version marker
+        working-directory: packages/react-native
+        run: |
+          VERSION=$(node -p "require('./package.json').version")
+          echo "${VERSION}-Debug" > .build/artifacts/hermes/version.txt
+
+      - name: Setup SPM workspace (using prebuilt Hermes)
+        working-directory: packages/react-native
+        run: node scripts/ios-prebuild.js -s -f Debug
+
+      - name: Build SPM (${{ matrix.platform }})
+        working-directory: packages/react-native
+        run: node scripts/ios-prebuild.js -b -f Debug -p ${{ matrix.platform }}
diff --git a/.github/workflows/microsoft-pr.yml b/.github/workflows/microsoft-pr.yml
index 968a5d5d9bf3..a1d3d2d4c274 100644
--- a/.github/workflows/microsoft-pr.yml
+++ b/.github/workflows/microsoft-pr.yml
@@ -132,6 +132,11 @@ jobs:
     permissions: {}
     uses: ./.github/workflows/microsoft-build-rntester.yml
 
+  build-spm:
+    name: "Build SPM"
+    permissions: {}
+    uses: ./.github/workflows/microsoft-build-spm.yml
+
   test-react-native-macos-init:
     name: "Test react-native-macos init"
     permissions: {}
@@ -156,6 +161,7 @@ jobs:
       - yarn-constraints
       - javascript-tests
       - build-rntester
+      - build-spm
       - test-react-native-macos-init
       # - react-native-test-app-integration
     steps:
diff --git a/packages/react-native/Package.swift b/packages/react-native/Package.swift
index c748b549463b..8c9210c0bdb0 100644
--- a/packages/react-native/Package.swift
+++ b/packages/react-native/Package.swift
@@ -249,7 +249,13 @@ let reactJsErrorHandler = RNTarget(
 let reactGraphicsApple = RNTarget(
   name: .reactGraphicsApple,
   path: "ReactCommon/react/renderer/graphics/platform/ios",
-  linkedFrameworks: ["UIKit", "CoreGraphics"],
+  linkedFrameworks: ["CoreGraphics"],
+  // [macOS] Package.swift evaluates on the host (macOS), not the target, so #if os(macOS) doesn't work for cross-compilation.
+  // not the target. Use .when(platforms:) for cross-compilation support.
+  platformLinkerSettings: [
+    .linkedFramework("UIKit", .when(platforms: [.iOS, .visionOS])),
+    .linkedFramework("AppKit", .when(platforms: [.macOS])),
+  ],
   dependencies: [.reactDebug, .jsi, .reactUtils, .reactNativeDependencies]
 )
 
@@ -363,12 +369,27 @@ let reactCore = RNTarget(
     "ReactCommon/react/runtime/platform/ios", // explicit header search path to break circular dependency. RCTHost imports `RCTDefines.h` in ReactCore, ReacCore needs to import RCTHost
   ],
   linkedFrameworks: ["CoreServices"],
+  // [macOS] RCTUIKit is part of React-Core on 0.81 — add platform-conditional UIKit/AppKit linking
+  platformLinkerSettings: [
+    .linkedFramework("UIKit", .when(platforms: [.iOS, .visionOS])),
+    .linkedFramework("AppKit", .when(platforms: [.macOS])),
+  ],
+  // macOS]
   excludedPaths: ["Fabric", "Tests", "Resources", "Runtime/RCTJscInstanceFactory.mm", "I18n/strings", "CxxBridge/JSCExecutorFactory.mm", "CoreModules"],
   dependencies: [.reactNativeDependencies, .reactCxxReact, .reactPerfLogger, .jsi, .reactJsiExecutor, .reactUtils, .reactFeatureFlags, .reactRuntimeScheduler, .yoga, .reactJsInspector, .reactJsiTooling, .rctDeprecation, .reactCoreRCTWebsocket, .reactRCTImage, .reactTurboModuleCore, .reactRCTText, .reactRCTBlob, .reactRCTAnimation, .reactRCTNetwork, .reactFabric, .hermesPrebuilt],
   sources: [".", "Runtime/RCTHermesInstanceFactory.mm"]
 )
 
 /// React-Fabric.podspec
+// [macOS: on macOS, use platform/macos view sources instead of platform/cxx
+#if os(macOS)
+let reactFabricViewPlatformSources = ["components/view/platform/macos"]
+let reactFabricViewPlatformExcludes = ["components/view/platform/cxx"]
+#else
+let reactFabricViewPlatformExcludes = ["components/view/platform/macos"]
+let reactFabricViewPlatformSources = ["components/view/platform/cxx"]
+#endif
+// macOS]
 let reactFabric = RNTarget(
   name: .reactFabric,
   path: "ReactCommon/react/renderer",
@@ -379,7 +400,8 @@ let reactFabric = RNTarget(
     "components/view/tests",
     "components/view/platform/android",
     "components/view/platform/windows",
-    "components/view/platform/macos",
+    // "components/view/platform/cxx", // [macOS] excluded on macOS, included on iOS/visionOS (see reactFabricViewPlatformExcludes)
+    // "components/view/platform/macos", // [macOS] excluded on iOS/visionOS, included on macOS (see reactFabricViewPlatformExcludes)
     "components/scrollview/tests",
     "components/scrollview/platform/android",
     "mounting/tests",
@@ -402,9 +424,9 @@ let reactFabric = RNTarget(
     "components/unimplementedview",
     "components/virtualview",
     "components/root/tests",
-  ],
+  ] + reactFabricViewPlatformExcludes, // [macOS]
   dependencies: [.reactNativeDependencies, .reactJsiExecutor, .rctTypesafety, .reactTurboModuleCore, .jsi, .logger, .reactDebug, .reactFeatureFlags, .reactUtils, .reactRuntimeScheduler, .reactCxxReact, .reactRendererDebug, .reactGraphics, .yoga],
-  sources: ["animations", "attributedstring", "core", "componentregistry", "componentregistry/native", "components/root", "components/view", "components/view/platform/cxx", "components/scrollview", "components/scrollview/platform/cxx", "components/legacyviewmanagerinterop", "dom", "scheduler", "mounting", "observers/events", "telemetry", "consistency", "leakchecker", "uimanager", "uimanager/consistency"]
+  sources: ["animations", "attributedstring", "core", "componentregistry", "componentregistry/native", "components/root", "components/view", "components/scrollview", "components/scrollview/platform/cxx", "components/legacyviewmanagerinterop", "dom", "scheduler", "mounting", "observers/events", "telemetry", "consistency", "leakchecker", "uimanager", "uimanager/consistency"] + reactFabricViewPlatformSources // [macOS]
 )
 
 /// React-RCTFabric.podspec
@@ -424,7 +446,8 @@ let reactFabricComponents = RNTarget(
     "components/view/platform/android",
     "components/view/platform/windows",
     "components/view/platform/macos",
-    "components/switch/iosswitch/react/renderer/components/switch/MacOSSwitchShadowNode.mm",
+    // [macOS] Both IOSSwitchShadowNode.mm and MacOSSwitchShadowNode.mm are included;
+    // they use #if TARGET_OS_OSX guards internally so only the correct one compiles.
     "components/textinput/platform/android",
     "components/text/platform/android",
     "components/textinput/platform/macos",
@@ -591,7 +614,7 @@ let targets = [
 
 let package = Package(
   name: react,
-  platforms: [.iOS(.v15), .macCatalyst(SupportedPlatform.MacCatalystVersion.v13)],
+  platforms: [.iOS(.v15), .macOS(.v14) /* [macOS] */, .macCatalyst(SupportedPlatform.MacCatalystVersion.v13)],
   products: [
     .library(
       name: react,
@@ -632,14 +655,16 @@ class BinaryTarget: BaseTarget {
 
 class RNTarget: BaseTarget {
   let linkedFrameworks: [String]
+  let platformLinkerSettings: [LinkerSetting] // [macOS] Platform-conditional framework linking (e.g. UIKit vs AppKit)
   let excludedPaths: [String]
   let dependencies: [String]
   let sources: [String]?
   let publicHeadersPath: String?
   let defines: [CXXSetting]
 
-  init(name: String, path: String, searchPaths: [String] = [], linkedFrameworks: [String] = [], excludedPaths: [String] = [], dependencies: [String] = [], sources: [String]? = nil, publicHeadersPath: String? = ".", defines: [CXXSetting] = []) {
+  init(name: String, path: String, searchPaths: [String] = [], linkedFrameworks: [String] = [], platformLinkerSettings: [LinkerSetting] = [], excludedPaths: [String] = [], dependencies: [String] = [], sources: [String]? = nil, publicHeadersPath: String? = ".", defines: [CXXSetting] = []) {
     self.linkedFrameworks = linkedFrameworks
+    self.platformLinkerSettings = platformLinkerSettings
     self.excludedPaths = excludedPaths
     self.dependencies = dependencies
     self.sources = sources
@@ -675,7 +700,7 @@ class RNTarget: BaseTarget {
   override func target(targets: [BaseTarget]) -> Target {
     let searchPaths: [String] = self.headerSearchPaths(targets: targets)
 
-    let linkerSettings = self.linkedFrameworks.reduce([]) { $0 + [LinkerSetting.linkedFramework($1)] }
+    let linkerSettings = self.linkedFrameworks.reduce([]) { $0 + [LinkerSetting.linkedFramework($1)] } + self.platformLinkerSettings // [macOS]
 
     return Target.reactNativeTarget(
       name: self.name,
diff --git a/packages/react-native/ReactCommon/react/renderer/components/switch/iosswitch/react/renderer/components/switch/IOSSwitchShadowNode.mm b/packages/react-native/ReactCommon/react/renderer/components/switch/iosswitch/react/renderer/components/switch/IOSSwitchShadowNode.mm
index d1981f17c062..7b8bc2e7d380 100644
--- a/packages/react-native/ReactCommon/react/renderer/components/switch/iosswitch/react/renderer/components/switch/IOSSwitchShadowNode.mm
+++ b/packages/react-native/ReactCommon/react/renderer/components/switch/iosswitch/react/renderer/components/switch/IOSSwitchShadowNode.mm
@@ -5,6 +5,9 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+#include <TargetConditionals.h> // [macOS]
+#if !TARGET_OS_OSX // [macOS]
+
 #import <React/RCTUtils.h>
 #import <UIKit/UIKit.h>
 #include "AppleSwitchShadowNode.h"
@@ -26,3 +29,5 @@
 }
 
 } // namespace facebook::react
+
+#endif // !TARGET_OS_OSX [macOS]
diff --git a/packages/react-native/ReactCommon/react/renderer/components/switch/iosswitch/react/renderer/components/switch/MacOSSwitchShadowNode.mm b/packages/react-native/ReactCommon/react/renderer/components/switch/iosswitch/react/renderer/components/switch/MacOSSwitchShadowNode.mm
index cd62f626ba68..ec76095bc8e0 100644
--- a/packages/react-native/ReactCommon/react/renderer/components/switch/iosswitch/react/renderer/components/switch/MacOSSwitchShadowNode.mm
+++ b/packages/react-native/ReactCommon/react/renderer/components/switch/iosswitch/react/renderer/components/switch/MacOSSwitchShadowNode.mm
@@ -5,6 +5,9 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+#include <TargetConditionals.h> // [macOS]
+#if TARGET_OS_OSX // [macOS]
+
 #import <AppKit/AppKit.h>
 #include "AppleSwitchShadowNode.h"
 
@@ -30,3 +33,5 @@
 }
 
 } // namespace facebook::react
+
+#endif // TARGET_OS_OSX [macOS]
diff --git a/packages/react-native/scripts/ios-prebuild/cli.js b/packages/react-native/scripts/ios-prebuild/cli.js
index 01301c800af7..c2f3586f46f5 100644
--- a/packages/react-native/scripts/ios-prebuild/cli.js
+++ b/packages/react-native/scripts/ios-prebuild/cli.js
@@ -18,6 +18,8 @@ const platforms /*: $ReadOnlyArray<Platform> */ = [
   'ios',
   'ios-simulator',
   'mac-catalyst',
+  'macos', // [macOS]
+  'visionos', // [macOS]
 ];
 
 // CI can't use commas in cache keys, so 'macOS,variant=Mac Catalyst' was creating troubles
@@ -26,6 +28,8 @@ const platformToDestination /*: $ReadOnly<{|[Platform]: Destination|}> */ = {
   ios: 'iOS',
   'ios-simulator': 'iOS Simulator',
   'mac-catalyst': 'macOS,variant=Mac Catalyst',
+  macos: 'macOS', // [macOS]
+  visionos: 'visionOS', // [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 e5e67bfcb0a6..6c3e9859a32a 100644
--- a/packages/react-native/scripts/ios-prebuild/hermes.js
+++ b/packages/react-native/scripts/ios-prebuild/hermes.js
@@ -8,9 +8,14 @@
  * @format
  */
 
+const {
+  findMatchingHermesVersion,
+  hermesCommitAtMergeBase,
+} = require('./macosVersionResolver'); // [macOS]
 const {computeNightlyTarballURL, createLogger} = require('./utils');
 const {execSync} = require('child_process');
 const fs = require('fs');
+const os = require('os'); // [macOS]
 const path = require('path');
 const stream = require('stream');
 const {promisify} = require('util');
@@ -56,6 +61,29 @@ async function prepareHermesArtifactsAsync(
     // Resolve the version from the environment variable or use the default version
     let resolvedVersion = process.env.HERMES_VERSION ?? version;
 
+    // [macOS] Map macOS version to upstream RN version for artifact lookup.
+    // If no mapped version is found (main branch / 1000.0.0), allowBuildFromSource
+    // enables the fallback to hermesCommitAtMergeBase() when no prebuilt artifacts exist.
+    let allowBuildFromSource = false;
+    if (!process.env.HERMES_VERSION) {
+      const packageJsonPath = path.resolve(
+        __dirname,
+        '..',
+        '..',
+        'package.json',
+      );
+      const mappedVersion = findMatchingHermesVersion(packageJsonPath);
+      if (mappedVersion != null) {
+        hermesLog(
+          `Using mapped upstream version for Hermes lookup: ${mappedVersion}`,
+        );
+        resolvedVersion = mappedVersion;
+      } else {
+        allowBuildFromSource = true;
+      }
+    }
+    // macOS]
+
     if (resolvedVersion === 'nightly') {
       hermesLog('Using latest nightly tarball');
       const hermesVersion = await getNightlyVersionFromNPM();
@@ -74,7 +102,11 @@ async function prepareHermesArtifactsAsync(
       return artifactsPath;
     }
 
-    const sourceType = await hermesSourceType(resolvedVersion, buildType);
+    const sourceType = await hermesSourceType(
+      resolvedVersion,
+      buildType,
+      allowBuildFromSource,
+    );
     localPath = await resolveSourceFromSourceType(
       sourceType,
       resolvedVersion,
@@ -124,12 +156,14 @@ type HermesEngineSourceType =
   | 'local_prebuilt_tarball'
   | 'download_prebuild_tarball'
   | 'download_prebuilt_nightly_tarball'
+  | 'build_from_hermes_commit'
 */
 
 const HermesEngineSourceTypes = {
     LOCAL_PREBUILT_TARBALL: 'local_prebuilt_tarball',
     DOWNLOAD_PREBUILD_TARBALL: 'download_prebuild_tarball',
     DOWNLOAD_PREBUILT_NIGHTLY_TARBALL: 'download_prebuilt_nightly_tarball',
+    BUILD_FROM_HERMES_COMMIT: 'build_from_hermes_commit', // [macOS]
   } /*:: as const */;
 
 /**
@@ -224,10 +258,16 @@ async function hermesArtifactExists(
 
 /**
  * Determines the source type for Hermes based on availability
+ *
+ * @param version - The resolved version string
+ * @param buildType - Debug or Release
+ * @param allowBuildFromSource - If true (macOS main branch), fall back to BUILD_FROM_HERMES_COMMIT
+ *   when no prebuilt artifacts exist. If false, fall back to nightly download (original behavior).
  */
 async function hermesSourceType(
   version /*: string */,
   buildType /*: BuildFlavor */,
+  allowBuildFromSource /*: boolean */ = false,
 ) /*: Promise<HermesEngineSourceType> */ {
   if (hermesEngineTarballEnvvarDefined()) {
     hermesLog('Using local prebuild tarball');
@@ -247,6 +287,16 @@ async function hermesSourceType(
     return HermesEngineSourceTypes.DOWNLOAD_PREBUILT_NIGHTLY_TARBALL;
   }
 
+  // [macOS] When on the macOS main branch (no mapped version, no explicit HERMES_VERSION),
+  // fall back to resolving the Hermes commit at the merge base with facebook/react-native.
+  if (allowBuildFromSource) {
+    hermesLog(
+      'No prebuilt Hermes artifact found. Will attempt to resolve from merge base with facebook/react-native.',
+    );
+    return HermesEngineSourceTypes.BUILD_FROM_HERMES_COMMIT;
+  }
+  // macOS]
+
   hermesLog(
     'Using download prebuild nightly tarball - this is a fallback and might not work.',
   );
@@ -266,6 +316,8 @@ async function resolveSourceFromSourceType(
       return downloadPrebuildTarball(version, buildType, artifactsPath);
     case HermesEngineSourceTypes.DOWNLOAD_PREBUILT_NIGHTLY_TARBALL:
       return downloadPrebuiltNightlyTarball(version, buildType, artifactsPath);
+    case HermesEngineSourceTypes.BUILD_FROM_HERMES_COMMIT: // [macOS]
+      return buildFromHermesCommit(version, buildType, artifactsPath);
     default:
       abort(
         `[Hermes] Unsupported or invalid source type provided: ${sourceType}`,
@@ -372,6 +424,113 @@ async function downloadHermesTarball(
   return destPath;
 }
 
+// [macOS
+/**
+ * Handles the case where no prebuilt Hermes artifacts are available.
+ * Determines the Hermes commit at the merge base with facebook/react-native
+ * and provides actionable guidance for building Hermes.
+ */
+async function buildFromHermesCommit(
+  version /*: string */,
+  buildType /*: BuildFlavor */,
+  artifactsPath /*: string */,
+) /*: Promise<string> */ {
+  const {commit, timestamp} = hermesCommitAtMergeBase();
+  hermesLog(
+    `Building Hermes from source at commit ${commit} (merge base timestamp: ${timestamp})`,
+  );
+
+  const HERMES_GITHUB_URL = 'https://github.com/facebook/hermes.git';
+  const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'hermes-build-'));
+  const hermesDir = path.join(tmpDir, 'hermes');
+
+  try {
+    // Clone Hermes at the identified commit using the most efficient
+    // single-fetch pattern (see https://github.com/actions/checkout)
+    hermesLog(`Cloning Hermes at commit ${commit}...`);
+    execSync(`git init "${hermesDir}"`, {stdio: 'inherit'});
+    execSync(`git -C "${hermesDir}" remote add origin ${HERMES_GITHUB_URL}`, {
+      stdio: 'inherit',
+    });
+    execSync(
+      `git -C "${hermesDir}" fetch --no-tags --depth 1 origin +${commit}:refs/remotes/origin/main`,
+      {stdio: 'inherit', timeout: 300000},
+    );
+    execSync(`git -C "${hermesDir}" checkout main`, {stdio: 'inherit'});
+
+    const reactNativeRoot = path.resolve(__dirname, '..', '..');
+    const buildScript = path.join(
+      reactNativeRoot,
+      'sdks',
+      'hermes-engine',
+      'utils',
+      'build-ios-framework.sh',
+    );
+
+    const buildEnv = {
+      ...process.env,
+      BUILD_TYPE: buildType,
+      HERMES_PATH: hermesDir,
+      JSI_PATH: path.join(hermesDir, 'API', 'jsi'),
+      REACT_NATIVE_PATH: reactNativeRoot,
+      // Deployment targets matching react-native-macos minimums
+      IOS_DEPLOYMENT_TARGET: '15.1',
+      MAC_DEPLOYMENT_TARGET: '14.0',
+      XROS_DEPLOYMENT_TARGET: '1.0',
+      RELEASE_VERSION: version,
+    };
+
+    hermesLog(`Building Hermes frameworks (${buildType})...`);
+    execSync(`bash "${buildScript}"`, {
+      cwd: hermesDir,
+      stdio: 'inherit',
+      timeout: 3600000, // 60 minutes
+      env: buildEnv,
+    });
+
+    // Create tarball from the destroot (same structure as Maven artifacts)
+    const tarballName = `hermes-ios-${buildType.toLowerCase()}.tar.gz`;
+    const tarballPath = path.join(artifactsPath, tarballName);
+    hermesLog('Creating Hermes tarball from build output...');
+    execSync(`tar -czf "${tarballPath}" -C "${hermesDir}" destroot`, {
+      stdio: 'inherit',
+    });
+
+    hermesLog(`Hermes built from source and packaged at ${tarballPath}`);
+    return tarballPath;
+  } catch (e) {
+    // Dump CMake error logs before cleanup for debugging
+    try {
+      const cmakeErrorLog = path.join(
+        hermesDir,
+        'build_host_hermesc',
+        'CMakeFiles',
+        'CMakeError.log',
+      );
+      if (fs.existsSync(cmakeErrorLog)) {
+        hermesLog('=== CMakeError.log ===');
+        hermesLog(fs.readFileSync(cmakeErrorLog, 'utf8'));
+      }
+    } catch (_) {
+      // ignore
+    }
+
+    abort(
+      `[Hermes] Failed to build Hermes from source at commit ${commit}.\n` +
+        `Error: ${e.message}\n` +
+        `To resolve, either:\n` +
+        `  1. Set HERMES_ENGINE_TARBALL_PATH to a local Hermes tarball path\n` +
+        `  2. Set HERMES_VERSION to an upstream RN version with published artifacts\n` +
+        `  3. Build Hermes manually from commit ${commit} and provide the tarball path via HERMES_ENGINE_TARBALL_PATH`,
+    );
+    return ''; // unreachable
+  } finally {
+    // Clean up
+    fs.rmSync(tmpDir, {recursive: true, force: true});
+  }
+}
+// macOS]
+
 function abort(message /*: string */) {
   hermesLog(message, 'error');
   throw new Error(message);
@@ -379,4 +538,6 @@ function abort(message /*: string */) {
 
 module.exports = {
   prepareHermesArtifactsAsync,
+  findMatchingHermesVersion, // [macOS] re-exported from macosVersionResolver.js
+  hermesCommitAtMergeBase, // [macOS] re-exported from macosVersionResolver.js
 };
diff --git a/packages/react-native/scripts/ios-prebuild/macosVersionResolver.js b/packages/react-native/scripts/ios-prebuild/macosVersionResolver.js
new file mode 100644
index 000000000000..4654117f97a2
--- /dev/null
+++ b/packages/react-native/scripts/ios-prebuild/macosVersionResolver.js
@@ -0,0 +1,199 @@
+/**
+ * Copyright (c) Microsoft Corporation.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * [macOS] This file is specific to react-native-macos and has no upstream equivalent.
+ * It handles version resolution for macOS fork branches where the package version
+ * differs from upstream react-native.
+ *
+ * @flow
+ * @format
+ */
+
+const {createLogger} = require('./utils');
+const {execSync} = require('child_process');
+const fs = require('fs');
+const os = require('os');
+const path = require('path');
+
+const macosLog = createLogger('macOS');
+
+/**
+ * For react-native-macos stable branches, maps the macOS package version
+ * to the upstream react-native version using peerDependencies.
+ * Returns null for version 1000.0.0 (main branch dev version).
+ *
+ * This is the JavaScript equivalent of the Ruby `findMatchingHermesVersion`
+ * in sdks/hermes-engine/hermes-utils.rb.
+ */
+function findMatchingHermesVersion(
+  packageJsonPath /*: string */,
+) /*: ?string */ {
+  const pkg = JSON.parse(fs.readFileSync(packageJsonPath, 'utf8'));
+
+  if (pkg.version === '1000.0.0') {
+    macosLog(
+      'Main branch detected (1000.0.0), no matching upstream Hermes version',
+    );
+    return null;
+  }
+
+  if (pkg.peerDependencies && pkg.peerDependencies['react-native']) {
+    const upstreamVersion = pkg.peerDependencies['react-native'];
+    macosLog(
+      `Mapped macOS version ${pkg.version} to upstream RN version: ${upstreamVersion}`,
+    );
+    return upstreamVersion;
+  }
+
+  macosLog(
+    'No matching Hermes version found in peerDependencies. Defaulting to package version.',
+  );
+  return null;
+}
+
+/**
+ * Finds the Hermes commit at the merge base with facebook/react-native.
+ * Used on the main branch (1000.0.0) where no prebuilt artifacts exist.
+ *
+ * Since react-native-macos lags slightly behind facebook/react-native, we can't always use
+ * the latest Hermes commit because Hermes and JSI don't always guarantee backwards compatibility.
+ * Instead, we take the commit hash of Hermes at the time of the merge base with facebook/react-native.
+ *
+ * This is the JavaScript equivalent of the Ruby `hermes_commit_at_merge_base`
+ * in sdks/hermes-engine/hermes-utils.rb.
+ */
+function hermesCommitAtMergeBase() /*: {| commit: string, timestamp: string |} */ {
+  const HERMES_GITHUB_URL = 'https://github.com/facebook/hermes.git';
+
+  // Fetch upstream react-native
+  macosLog('Fetching facebook/react-native to find merge base...');
+  try {
+    execSync('git fetch -q https://github.com/facebook/react-native.git', {
+      stdio: 'pipe',
+    });
+  } catch (e) {
+    abort(
+      '[Hermes] Failed to fetch facebook/react-native into the local repository.',
+    );
+  }
+
+  // Find merge base between our HEAD and upstream's HEAD
+  const mergeBase = execSync('git merge-base FETCH_HEAD HEAD', {
+    encoding: 'utf8',
+  }).trim();
+  if (!mergeBase) {
+    abort(
+      "[Hermes] Unable to find the merge base between our HEAD and upstream's HEAD.",
+    );
+  }
+
+  // Get timestamp of merge base
+  const timestamp = execSync(`git show -s --format=%ci ${mergeBase}`, {
+    encoding: 'utf8',
+  }).trim();
+  if (!timestamp) {
+    abort(
+      `[Hermes] Unable to extract the timestamp for the merge base (${mergeBase}).`,
+    );
+  }
+
+  // Clone Hermes bare (minimal) into a temp directory and find the commit
+  macosLog(
+    `Merge base timestamp: ${timestamp}. Cloning Hermes to find matching commit...`,
+  );
+  const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'hermes-'));
+  const hermesGitDir = path.join(tmpDir, 'hermes.git');
+
+  try {
+    // Explicitly use Hermes 'main' branch since the default branch changed to 'static_h' (Hermes V1)
+    execSync(
+      `git clone -q --bare --filter=blob:none --single-branch --branch main ${HERMES_GITHUB_URL} "${hermesGitDir}"`,
+      {stdio: 'pipe', timeout: 120000},
+    );
+
+    // Find the Hermes commit at the time of the merge base on branch 'main'
+    const commit = execSync(
+      `git --git-dir="${hermesGitDir}" rev-list -1 --before="${timestamp}" refs/heads/main`,
+      {encoding: 'utf8'},
+    ).trim();
+
+    if (!commit) {
+      abort(
+        `[Hermes] Unable to find the Hermes commit hash at time ${timestamp} on branch 'main'.`,
+      );
+    }
+
+    macosLog(
+      `Using Hermes commit from the merge base with facebook/react-native: ${commit} (timestamp: ${timestamp})`,
+    );
+    return {commit, timestamp};
+  } finally {
+    // Clean up temp directory
+    fs.rmSync(tmpDir, {recursive: true, force: true});
+  }
+}
+
+/**
+ * Finds the upstream react-native version at the merge base with facebook/react-native.
+ * Falls back to null if the version at merge base is also 1000.0.0 (i.e. merge base is
+ * on upstream main, not a release branch).
+ */
+function findVersionAtMergeBase() /*: ?string */ {
+  try {
+    // hermesCommitAtMergeBase() already fetches facebook/react-native, but we
+    // might not have FETCH_HEAD if this runs standalone. Fetch it.
+    execSync('git fetch -q https://github.com/facebook/react-native.git', {
+      stdio: 'pipe',
+      timeout: 60000,
+    });
+    const mergeBase = execSync('git merge-base FETCH_HEAD HEAD', {
+      encoding: 'utf8',
+    }).trim();
+    if (!mergeBase) {
+      return null;
+    }
+    // Read the package.json version at the merge base commit
+    const pkgJson = execSync(
+      `git show ${mergeBase}:packages/react-native/package.json`,
+      {encoding: 'utf8'},
+    );
+    const version = JSON.parse(pkgJson).version;
+    // If the merge base is also on main (1000.0.0), this doesn't help
+    if (version === '1000.0.0') {
+      return null;
+    }
+    return version;
+  } catch (_) {
+    return null;
+  }
+}
+
+async function getLatestStableVersionFromNPM() /*: Promise<string> */ {
+  const npmResponse /*: Response */ = await fetch(
+    'https://registry.npmjs.org/react-native/latest',
+  );
+
+  if (!npmResponse.ok) {
+    throw new Error(
+      `Couldn't get latest stable version from NPM: ${npmResponse.status} ${npmResponse.statusText}`,
+    );
+  }
+
+  const json = await npmResponse.json();
+  return json.version;
+}
+
+function abort(message /*: string */) {
+  macosLog(message, 'error');
+  throw new Error(message);
+}
+
+module.exports = {
+  findMatchingHermesVersion,
+  hermesCommitAtMergeBase,
+  findVersionAtMergeBase,
+  getLatestStableVersionFromNPM,
+};
diff --git a/packages/react-native/scripts/ios-prebuild/reactNativeDependencies.js b/packages/react-native/scripts/ios-prebuild/reactNativeDependencies.js
index 6b5880e98c11..56b8f5fe7142 100644
--- a/packages/react-native/scripts/ios-prebuild/reactNativeDependencies.js
+++ b/packages/react-native/scripts/ios-prebuild/reactNativeDependencies.js
@@ -10,6 +10,11 @@
 
 /*:: import type {BuildFlavor} from './types'; */
 
+const {
+  findMatchingHermesVersion,
+  findVersionAtMergeBase,
+  getLatestStableVersionFromNPM,
+} = require('./macosVersionResolver'); // [macOS]
 const {computeNightlyTarballURL, createLogger} = require('./utils');
 const {execSync} = require('child_process');
 const fs = require('fs');
@@ -44,6 +49,35 @@ async function prepareReactNativeDependenciesArtifactsAsync(
   // Resolve the version from the environment variable or use the default version
   let resolvedVersion = process.env.RN_DEP_VERSION ?? version;
 
+  // [macOS] Map macOS version to upstream RN version for artifact lookup.
+  // For stable branches, peerDependencies maps to the upstream version.
+  // For the main branch (1000.0.0), fall back to the latest stable RN release.
+  if (!process.env.RN_DEP_VERSION) {
+    const packageJsonPath = path.resolve(__dirname, '..', '..', 'package.json');
+    const mappedVersion = findMatchingHermesVersion(packageJsonPath);
+    if (mappedVersion != null) {
+      dependencyLog(
+        `Using mapped upstream version for ReactNativeDependencies lookup: ${mappedVersion}`,
+      );
+      resolvedVersion = mappedVersion;
+    } else if (resolvedVersion === '1000.0.0') {
+      const versionAtMergeBase = findVersionAtMergeBase();
+      if (versionAtMergeBase != null) {
+        dependencyLog(
+          `Main branch detected. Using upstream version at merge base for ReactNativeDependencies: ${versionAtMergeBase}`,
+        );
+        resolvedVersion = versionAtMergeBase;
+      } else {
+        const latestStable = await getLatestStableVersionFromNPM();
+        dependencyLog(
+          `Main branch detected. Using latest stable RN version for ReactNativeDependencies: ${latestStable}`,
+        );
+        resolvedVersion = latestStable;
+      }
+    }
+  }
+  // macOS]
+
   if (resolvedVersion === 'nightly') {
     dependencyLog('Using latest nightly tarball');
     const rnVersion = await getNightlyVersionFromNPM();
diff --git a/packages/react-native/scripts/ios-prebuild/setup.js b/packages/react-native/scripts/ios-prebuild/setup.js
index 65e34bb6e482..73fe69993f02 100644
--- a/packages/react-native/scripts/ios-prebuild/setup.js
+++ b/packages/react-native/scripts/ios-prebuild/setup.js
@@ -190,6 +190,16 @@ async function setup(
     'ReactCommon/react/renderer/components/view/platform/cxx',
     'ReactCommon/react/renderer/components/view',
   );
+  // [macOS - link macOS-specific view platform headers
+  link(
+    'ReactCommon/react/renderer/components/view/platform/macos',
+    'ReactCommon/react/renderer/components/view',
+  );
+  link(
+    'ReactCommon/react/renderer/components/view/platform/macos',
+    'react/renderer/components/view',
+  );
+  // macOS]
   link('ReactCommon/react/renderer/mounting');
   link('ReactCommon/react/renderer/attributedstring');
   link('ReactCommon/runtimeexecutor/ReactCommon', 'ReactCommon');
diff --git a/packages/react-native/scripts/ios-prebuild/types.js b/packages/react-native/scripts/ios-prebuild/types.js
index c1ac1489c804..87f516c5ba99 100644
--- a/packages/react-native/scripts/ios-prebuild/types.js
+++ b/packages/react-native/scripts/ios-prebuild/types.js
@@ -12,12 +12,16 @@
 export type Platform =
   'ios' |
   'ios-simulator' |
-  'mac-catalyst';
+  'mac-catalyst' |
+  'macos' |        // [macOS]
+  'visionos';      // [macOS]
 
 export type Destination =
   'iOS' |
   'iOS Simulator' |
-  'macOS,variant=Mac Catalyst';
+  'macOS,variant=Mac Catalyst' |
+  'macOS' |        // [macOS]
+  'visionOS';      // [macOS]
 
 export type BuildFlavor = 'Debug' | 'Release';
 */
diff --git a/packages/react-native/sdks/hermes-engine/utils/build-apple-framework.sh b/packages/react-native/sdks/hermes-engine/utils/build-apple-framework.sh
index 76b23e18970c..44ce6d663582 100755
--- a/packages/react-native/sdks/hermes-engine/utils/build-apple-framework.sh
+++ b/packages/react-native/sdks/hermes-engine/utils/build-apple-framework.sh
@@ -12,7 +12,7 @@ CURR_SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd -P)"
 IMPORT_HERMESC_PATH=${HERMES_OVERRIDE_HERMESC_PATH:-$PWD/build_host_hermesc/ImportHermesc.cmake}
 BUILD_TYPE=${BUILD_TYPE:-Debug}
 
-HERMES_PATH="$CURR_SCRIPT_DIR/.."
+HERMES_PATH=${HERMES_PATH:-"$CURR_SCRIPT_DIR/.."}
 REACT_NATIVE_PATH=${REACT_NATIVE_PATH:-$CURR_SCRIPT_DIR/../../..}
 
 NUM_CORES=$(sysctl -n hw.ncpu)
diff --git a/packages/react-native/sdks/hermes-engine/utils/build-ios-framework.sh b/packages/react-native/sdks/hermes-engine/utils/build-ios-framework.sh
index 08382b7d4deb..c6cd66001aed 100755
--- a/packages/react-native/sdks/hermes-engine/utils/build-ios-framework.sh
+++ b/packages/react-native/sdks/hermes-engine/utils/build-ios-framework.sh
@@ -10,7 +10,7 @@ fi
 set -e
 
 # Given a specific target, retrieve the right architecture for it
-# $1 the target you want to build. Allowed values: iphoneos, iphonesimulator, catalyst, xros, xrsimulator
+# $1 the target you want to build. Allowed values: iphoneos, iphonesimulator, catalyst, macosx, xros, xrsimulator
 function get_architecture {
     if [[ $1 == "iphoneos" || $1 == "xros" ]]; then
       echo "arm64"
@@ -20,7 +20,7 @@ function get_architecture {
       echo "arm64"
     elif [[ $1 == "appletvsimulator" ]]; then
       echo "x86_64;arm64"
-    elif [[ $1 == "catalyst" ]]; then
+    elif [[ $1 == "catalyst" || $1 == "macosx" ]]; then
       echo "x86_64;arm64"
     else
       echo "Error: unknown architecture passed $1"
@@ -29,7 +29,9 @@ function get_architecture {
 }
 
 function get_deployment_target {
-    if [[ $1 == "xros" || $1 == "xrsimulator" ]]; then
+    if [[ $1 == "macosx" ]]; then
+      echo "$(get_mac_deployment_target)"
+    elif [[ $1 == "xros" || $1 == "xrsimulator" ]]; then
       echo "$(get_visionos_deployment_target)"
     else # tvOS and iOS use the same deployment target
       echo "$(get_ios_deployment_target)"
@@ -53,7 +55,7 @@ function build_framework {
 # group the frameworks together to create a universal framework
 function build_universal_framework {
     if [ ! -d destroot/Library/Frameworks/universal/hermes.xcframework ]; then
-        create_universal_framework "iphoneos" "iphonesimulator" "catalyst" "xros" "xrsimulator" "appletvos" "appletvsimulator"
+        create_universal_framework "macosx" "iphoneos" "iphonesimulator" "catalyst" "xros" "xrsimulator" "appletvos" "appletvsimulator"
     else
         echo "Skipping; Clean \"destroot\" to rebuild".
     fi
@@ -63,6 +65,7 @@ function build_universal_framework {
 # this is used to preserve backward compatibility
 function create_framework {
     if [ ! -d destroot/Library/Frameworks/universal/hermes.xcframework ]; then
+        build_framework "macosx"
         build_framework "iphoneos"
         build_framework "iphonesimulator"
         build_framework "appletvos"