diff --git a/packages/scheduler/src/forks/SchedulerHostConfig.post-task.js b/packages/scheduler/src/forks/SchedulerHostConfig.post-task.js
new file mode 100644
index 0000000000..b7e958911e
--- /dev/null
+++ b/packages/scheduler/src/forks/SchedulerHostConfig.post-task.js
@@ -0,0 +1,250 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {enableIsInputPending} from '../SchedulerFeatureFlags';
+
+export let requestHostCallback;
+export let cancelHostCallback;
+export let requestHostTimeout;
+export let cancelHostTimeout;
+export let shouldYieldToHost;
+export let requestPaint;
+export let getCurrentTime;
+export let forceFrameRate;
+
+if (
+  // If Scheduler runs in a non-DOM environment, it falls back to a naive
+  // implementation using setTimeout.
+  typeof window === 'undefined' ||
+  // Check if MessageChannel is supported, too.
+  typeof MessageChannel !== 'function'
+) {
+  // If this accidentally gets imported in a non-browser environment, e.g. JavaScriptCore,
+  // fallback to a naive implementation.
+  let _callback = null;
+  let _timeoutID = null;
+  const _flushCallback = function() {
+    if (_callback !== null) {
+      try {
+        const currentTime = getCurrentTime();
+        const hasRemainingTime = true;
+        _callback(hasRemainingTime, currentTime);
+        _callback = null;
+      } catch (e) {
+        setTimeout(_flushCallback, 0);
+        throw e;
+      }
+    }
+  };
+  const initialTime = Date.now();
+  getCurrentTime = function() {
+    return Date.now() - initialTime;
+  };
+  requestHostCallback = function(cb) {
+    if (_callback !== null) {
+      // Protect against re-entrancy.
+      setTimeout(requestHostCallback, 0, cb);
+    } else {
+      _callback = cb;
+      setTimeout(_flushCallback, 0);
+    }
+  };
+  cancelHostCallback = function() {
+    _callback = null;
+  };
+  requestHostTimeout = function(cb, ms) {
+    _timeoutID = setTimeout(cb, ms);
+  };
+  cancelHostTimeout = function() {
+    clearTimeout(_timeoutID);
+  };
+  shouldYieldToHost = function() {
+    return false;
+  };
+  requestPaint = forceFrameRate = function() {};
+} else {
+  // Capture local references to native APIs, in case a polyfill overrides them.
+  const performance = window.performance;
+  const Date = window.Date;
+  const setTimeout = window.setTimeout;
+  const clearTimeout = window.clearTimeout;
+
+  if (typeof console !== 'undefined') {
+    // TODO: Scheduler no longer requires these methods to be polyfilled. But
+    // maybe we want to continue warning if they don't exist, to preserve the
+    // option to rely on it in the future?
+    const requestAnimationFrame = window.requestAnimationFrame;
+    const cancelAnimationFrame = window.cancelAnimationFrame;
+    // TODO: Remove fb.me link
+    if (typeof requestAnimationFrame !== 'function') {
+      // Using console['error'] to evade Babel and ESLint
+      console['error'](
+        "This browser doesn't support requestAnimationFrame. " +
+          'Make sure that you load a ' +
+          'polyfill in older browsers. https://fb.me/react-polyfills',
+      );
+    }
+    if (typeof cancelAnimationFrame !== 'function') {
+      // Using console['error'] to evade Babel and ESLint
+      console['error'](
+        "This browser doesn't support cancelAnimationFrame. " +
+          'Make sure that you load a ' +
+          'polyfill in older browsers. https://fb.me/react-polyfills',
+      );
+    }
+  }
+
+  if (
+    typeof performance === 'object' &&
+    typeof performance.now === 'function'
+  ) {
+    getCurrentTime = () => performance.now();
+  } else {
+    const initialTime = Date.now();
+    getCurrentTime = () => Date.now() - initialTime;
+  }
+
+  let isMessageLoopRunning = false;
+  let scheduledHostCallback = null;
+  let taskTimeoutID = -1;
+
+  // Scheduler periodically yields in case there is other work on the main
+  // thread, like user events. By default, it yields multiple times per frame.
+  // It does not attempt to align with frame boundaries, since most tasks don't
+  // need to be frame aligned; for those that do, use requestAnimationFrame.
+  let yieldInterval = 5;
+  let deadline = 0;
+
+  // TODO: Make this configurable
+  // TODO: Adjust this based on priority?
+  const maxYieldInterval = 300;
+  let needsPaint = false;
+
+  if (
+    enableIsInputPending &&
+    navigator !== undefined &&
+    navigator.scheduling !== undefined &&
+    navigator.scheduling.isInputPending !== undefined
+  ) {
+    const scheduling = navigator.scheduling;
+    shouldYieldToHost = function() {
+      const currentTime = getCurrentTime();
+      if (currentTime >= deadline) {
+        // There's no time left. We may want to yield control of the main
+        // thread, so the browser can perform high priority tasks. The main ones
+        // are painting and user input. If there's a pending paint or a pending
+        // input, then we should yield. But if there's neither, then we can
+        // yield less often while remaining responsive. We'll eventually yield
+        // regardless, since there could be a pending paint that wasn't
+        // accompanied by a call to `requestPaint`, or other main thread tasks
+        // like network events.
+        if (needsPaint || scheduling.isInputPending()) {
+          // There is either a pending paint or a pending input.
+          return true;
+        }
+        // There's no pending input. Only yield if we've reached the max
+        // yield interval.
+        return currentTime >= maxYieldInterval;
+      } else {
+        // There's still time left in the frame.
+        return false;
+      }
+    };
+
+    requestPaint = function() {
+      needsPaint = true;
+    };
+  } else {
+    // `isInputPending` is not available. Since we have no way of knowing if
+    // there's pending input, always yield at the end of the frame.
+    shouldYieldToHost = function() {
+      return getCurrentTime() >= deadline;
+    };
+
+    // Since we yield every frame regardless, `requestPaint` has no effect.
+    requestPaint = function() {};
+  }
+
+  forceFrameRate = function(fps) {
+    if (fps < 0 || fps > 125) {
+      // Using console['error'] to evade Babel and ESLint
+      console['error'](
+        'forceFrameRate takes a positive int between 0 and 125, ' +
+          'forcing frame rates higher than 125 fps is not unsupported',
+      );
+      return;
+    }
+    if (fps > 0) {
+      yieldInterval = Math.floor(1000 / fps);
+    } else {
+      // reset the framerate
+      yieldInterval = 5;
+    }
+  };
+
+  const performWorkUntilDeadline = () => {
+    if (scheduledHostCallback !== null) {
+      const currentTime = getCurrentTime();
+      // Yield after `yieldInterval` ms, regardless of where we are in the vsync
+      // cycle. This means there's always time remaining at the beginning of
+      // the message event.
+      deadline = currentTime + yieldInterval;
+      const hasTimeRemaining = true;
+      try {
+        const hasMoreWork = scheduledHostCallback(
+          hasTimeRemaining,
+          currentTime,
+        );
+        if (!hasMoreWork) {
+          isMessageLoopRunning = false;
+          scheduledHostCallback = null;
+        } else {
+          // If there's more work, schedule the next message event at the end
+          // of the preceding one.
+          port.postMessage(null);
+        }
+      } catch (error) {
+        // If a scheduler task throws, exit the current browser task so the
+        // error can be observed.
+        port.postMessage(null);
+        throw error;
+      }
+    } else {
+      isMessageLoopRunning = false;
+    }
+    // Yielding to the browser will give it a chance to paint, so we can
+    // reset this.
+    needsPaint = false;
+  };
+
+  const channel = new MessageChannel();
+  const port = channel.port2;
+  channel.port1.onmessage = performWorkUntilDeadline;
+
+  requestHostCallback = function(callback) {
+    scheduledHostCallback = callback;
+    if (!isMessageLoopRunning) {
+      isMessageLoopRunning = true;
+      port.postMessage(null);
+    }
+  };
+
+  cancelHostCallback = function() {
+    scheduledHostCallback = null;
+  };
+
+  requestHostTimeout = function(callback, ms) {
+    taskTimeoutID = setTimeout(() => {
+      callback(getCurrentTime());
+    }, ms);
+  };
+
+  cancelHostTimeout = function() {
+    clearTimeout(taskTimeoutID);
+    taskTimeoutID = -1;
+  };
+}
diff --git a/packages/scheduler/unstable_post_task.js b/packages/scheduler/unstable_post_task.js
new file mode 100644
index 0000000000..aa14495a61
--- /dev/null
+++ b/packages/scheduler/unstable_post_task.js
@@ -0,0 +1,10 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+'use strict';
+
+export * from './src/Scheduler';
diff --git a/scripts/rollup/bundles.js b/scripts/rollup/bundles.js
index b255a1039b..4323001b61 100644
--- a/scripts/rollup/bundles.js
+++ b/scripts/rollup/bundles.js
@@ -634,6 +634,14 @@ const bundles = [
     externals: [],
   },
 
+  {
+    bundleTypes: [FB_WWW_DEV, FB_WWW_PROD, FB_WWW_PROFILING],
+    moduleType: ISOMORPHIC,
+    entry: 'scheduler/unstable_post_task',
+    global: 'SchedulerPostTask',
+    externals: [],
+  },
+
   /******* Jest React (experimental) *******/
   {
     bundleTypes: [NODE_DEV, NODE_PROD],
diff --git a/scripts/rollup/forks.js b/scripts/rollup/forks.js
index 80f1b724aa..5f2744e65b 100644
--- a/scripts/rollup/forks.js
+++ b/scripts/rollup/forks.js
@@ -198,6 +198,8 @@ const forks = Object.freeze({
       entry === 'react-test-renderer'
     ) {
       return 'scheduler/src/forks/SchedulerHostConfig.mock';
+    } else if (entry === 'scheduler/unstable_post_task') {
+      return 'scheduler/src/forks/SchedulerHostConfig.post-task';
     }
     return 'scheduler/src/forks/SchedulerHostConfig.default';
   },