diff --git a/.circleci/config.yml b/.circleci/config.yml
index 2a73417bdc..6f61ffbc6f 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -226,6 +226,7 @@ jobs:
     executor: default-executor
     steps:
       - checkout
+      - init_environment
       - run:
           name: Rebase PR on target branch
           # After checkout, rebase on top of target branch.
@@ -244,7 +245,6 @@ jobs:
           keys:
             - *cache_key
             - *cache_key_fallback
-      - init_environment
       - run:
           name: Running Yarn install
           command: yarn install --frozen-lockfile --non-interactive
diff --git a/.circleci/env.sh b/.circleci/env.sh
index 2b20833205..84affc8b57 100755
--- a/.circleci/env.sh
+++ b/.circleci/env.sh
@@ -3,72 +3,87 @@
 # Variables
 readonly projectDir=$(realpath "$(dirname ${BASH_SOURCE[0]})/..")
 readonly envHelpersPath="$projectDir/.circleci/env-helpers.inc.sh";
+readonly bashEnvCachePath="$projectDir/.circleci/bash_env_cache";
 
-# Load helpers and make them available everywhere (through `$BASH_ENV`).
-source $envHelpersPath;
-echo "source $envHelpersPath;" >> $BASH_ENV;
+if [ -f $bashEnvCachePath ]; then
+  # Since a bash env cache is present, load this into the $BASH_ENV
+  cat "$bashEnvCachePath" >> $BASH_ENV;
+  echo "BASH environment loaded from cached value at $bashEnvCachePath";
+else
+  # Since no bash env cache is present, build out $BASH_ENV values.
+
+  # Load helpers and make them available everywhere (through `$BASH_ENV`).
+  source $envHelpersPath;
+  echo "source $envHelpersPath;" >> $BASH_ENV;
 
 
-####################################################################################################
-# Define PUBLIC environment variables for CircleCI.
-####################################################################################################
-# See https://circleci.com/docs/2.0/env-vars/#built-in-environment-variables for more info.
-####################################################################################################
-setPublicVar PROJECT_ROOT "$projectDir";
-setPublicVar CI_AIO_MIN_PWA_SCORE "95";
-# This is the branch being built; e.g. `pull/12345` for PR builds.
-setPublicVar CI_BRANCH "$CIRCLE_BRANCH";
-setPublicVar CI_BUILD_URL "$CIRCLE_BUILD_URL";
-setPublicVar CI_COMMIT "$CIRCLE_SHA1";
-# `CI_COMMIT_RANGE` is only used on push builds (a.k.a. non-PR, non-scheduled builds and rerun
-# workflows of such builds).
-setPublicVar CI_COMMIT_RANGE "$CIRCLE_GIT_BASE_REVISION..$CIRCLE_GIT_REVISION";
-setPublicVar CI_PULL_REQUEST "${CIRCLE_PR_NUMBER:-false}";
-setPublicVar CI_REPO_NAME "$CIRCLE_PROJECT_REPONAME";
-setPublicVar CI_REPO_OWNER "$CIRCLE_PROJECT_USERNAME";
+  ####################################################################################################
+  # Define PUBLIC environment variables for CircleCI.
+  ####################################################################################################
+  # See https://circleci.com/docs/2.0/env-vars/#built-in-environment-variables for more info.
+  ####################################################################################################
+  setPublicVar PROJECT_ROOT "$projectDir";
+  setPublicVar CI_AIO_MIN_PWA_SCORE "95";
+  # This is the branch being built; e.g. `pull/12345` for PR builds.
+  setPublicVar CI_BRANCH "$CIRCLE_BRANCH";
+  setPublicVar CI_BUILD_URL "$CIRCLE_BUILD_URL";
+  setPublicVar CI_COMMIT "$CIRCLE_SHA1";
+  # `CI_COMMIT_RANGE` is only used on push builds (a.k.a. non-PR, non-scheduled builds and rerun
+  # workflows of such builds).
+  setPublicVar CI_COMMIT_RANGE "$CIRCLE_GIT_BASE_REVISION..$CIRCLE_GIT_REVISION";
+  setPublicVar CI_PULL_REQUEST "${CIRCLE_PR_NUMBER:-false}";
+  setPublicVar CI_REPO_NAME "$CIRCLE_PROJECT_REPONAME";
+  setPublicVar CI_REPO_OWNER "$CIRCLE_PROJECT_USERNAME";
+
+  # Store a PR's refs and shas so they don't need to be requested multiple times.
+  setPublicVar GITHUB_REFS_AND_SHAS $(node tools/utils/get-refs-and-shas-for-target.js ${CIRCLE_PR_NUMBER:-false} | awk '{ gsub(/"/,"\\\"") } 1');
 
 
-####################################################################################################
-# Define "lazy" PUBLIC environment variables for CircleCI.
-# (I.e. functions to set an environment variable when called.)
-####################################################################################################
-createPublicVarSetter CI_STABLE_BRANCH "\$(npm info @angular/core dist-tags.latest | sed -r 's/^\\s*([0-9]+\\.[0-9]+)\\.[0-9]+.*$/\\1.x/')";
+  ####################################################################################################
+  # Define "lazy" PUBLIC environment variables for CircleCI.
+  # (I.e. functions to set an environment variable when called.)
+  ####################################################################################################
+  createPublicVarSetter CI_STABLE_BRANCH "\$(npm info @angular/core dist-tags.latest | sed -r 's/^\\s*([0-9]+\\.[0-9]+)\\.[0-9]+.*$/\\1.x/')";
 
 
-####################################################################################################
-# Define SECRET environment variables for CircleCI.
-####################################################################################################
-setSecretVar CI_SECRET_AIO_DEPLOY_FIREBASE_TOKEN "$AIO_DEPLOY_TOKEN";
-setSecretVar CI_SECRET_PAYLOAD_FIREBASE_TOKEN "$ANGULAR_PAYLOAD_TOKEN";
+  ####################################################################################################
+  # Define SECRET environment variables for CircleCI.
+  ####################################################################################################
+  setSecretVar CI_SECRET_AIO_DEPLOY_FIREBASE_TOKEN "$AIO_DEPLOY_TOKEN";
+  setSecretVar CI_SECRET_PAYLOAD_FIREBASE_TOKEN "$ANGULAR_PAYLOAD_TOKEN";
 
 
-####################################################################################################
-# Define SauceLabs environment variables for CircleCI.
-####################################################################################################
-setPublicVar SAUCE_USERNAME "angular-framework";
-setSecretVar SAUCE_ACCESS_KEY "0c731274ed5f-cbc9-16f4-021a-9835e39f";
-# TODO(josephperrott): Remove environment variables once all saucelabs tests are via bazel method.
-setPublicVar SAUCE_LOG_FILE /tmp/angular/sauce-connect.log
-setPublicVar SAUCE_READY_FILE /tmp/angular/sauce-connect-ready-file.lock
-setPublicVar SAUCE_PID_FILE /tmp/angular/sauce-connect-pid-file.lock
-setPublicVar SAUCE_TUNNEL_IDENTIFIER "angular-framework-${CIRCLE_BUILD_NUM}-${CIRCLE_NODE_INDEX}"
-# Amount of seconds we wait for sauceconnect to establish a tunnel instance. In order to not
-# acquire CircleCI instances for too long if sauceconnect failed, we need a connect timeout.
-setPublicVar SAUCE_READY_FILE_TIMEOUT 120
+  ####################################################################################################
+  # Define SauceLabs environment variables for CircleCI.
+  ####################################################################################################
+  setPublicVar SAUCE_USERNAME "angular-framework";
+  setSecretVar SAUCE_ACCESS_KEY "0c731274ed5f-cbc9-16f4-021a-9835e39f";
+  # TODO(josephperrott): Remove environment variables once all saucelabs tests are via bazel method.
+  setPublicVar SAUCE_LOG_FILE /tmp/angular/sauce-connect.log
+  setPublicVar SAUCE_READY_FILE /tmp/angular/sauce-connect-ready-file.lock
+  setPublicVar SAUCE_PID_FILE /tmp/angular/sauce-connect-pid-file.lock
+  setPublicVar SAUCE_TUNNEL_IDENTIFIER "angular-framework-${CIRCLE_BUILD_NUM}-${CIRCLE_NODE_INDEX}"
+  # Amount of seconds we wait for sauceconnect to establish a tunnel instance. In order to not
+  # acquire CircleCI instances for too long if sauceconnect failed, we need a connect timeout.
+  setPublicVar SAUCE_READY_FILE_TIMEOUT 120
 
 
-####################################################################################################
-# Define environment variables for the `angular/components` repo unit tests job.
-####################################################################################################
-# We specifically use a directory within "/tmp" here because we want the cloned repo to be
-# completely isolated from angular/angular in order to avoid any bad interactions between
-# their separate build setups. **NOTE**: When updating the temporary directory, also update
-# the `save_cache` path configuration in `config.yml`
-setPublicVar COMPONENTS_REPO_TMP_DIR "/tmp/angular-components-repo"
-setPublicVar COMPONENTS_REPO_URL "https://github.com/angular/components.git"
-setPublicVar COMPONENTS_REPO_BRANCH "master"
-# **NOTE**: When updating the commit SHA, also update the cache key in the CircleCI `config.yml`.
-setPublicVar COMPONENTS_REPO_COMMIT "598db096e668aa7e9debd56eedfd127b7a55e371"
+  ####################################################################################################
+  # Define environment variables for the `angular/components` repo unit tests job.
+  ####################################################################################################
+  # We specifically use a directory within "/tmp" here because we want the cloned repo to be
+  # completely isolated from angular/angular in order to avoid any bad interactions between
+  # their separate build setups. **NOTE**: When updating the temporary directory, also update
+  # the `save_cache` path configuration in `config.yml`
+  setPublicVar COMPONENTS_REPO_TMP_DIR "/tmp/angular-components-repo"
+  setPublicVar COMPONENTS_REPO_URL "https://github.com/angular/components.git"
+  setPublicVar COMPONENTS_REPO_BRANCH "master"
+  # **NOTE**: When updating the commit SHA, also update the cache key in the CircleCI `config.yml`.
+  setPublicVar COMPONENTS_REPO_COMMIT "598db096e668aa7e9debd56eedfd127b7a55e371"
+  
+  # Save the created BASH_ENV into the bash env cache file.
+  cat "$BASH_ENV" >> $bashEnvCachePath;
+fi
 
 
 ####################################################################################################
diff --git a/tools/utils/get-refs-and-shas-for-target.js b/tools/utils/get-refs-and-shas-for-target.js
index 42a8989069..7ee356a7f0 100644
--- a/tools/utils/get-refs-and-shas-for-target.js
+++ b/tools/utils/get-refs-and-shas-for-target.js
@@ -6,6 +6,11 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+// NOTE: When invoked directly via node, this script will take the first positional
+// arguement as to be the PR number, and log out the ref and sha information in its
+// JSON format.  For other usages, the function to get the ref and sha information
+// may be imported by another script to be invoked.
+
 // This script uses `console` to print messages to the user.
 // tslint:disable:no-console
 
@@ -16,7 +21,18 @@ const exec = util.promisify(child_process.exec);
 
 async function requestDataFromGithub(url) {
   // GitHub requires a user agent: https://developer.github.com/v3/#user-agent-required
-  const options = {headers: {'User-Agent': 'angular'}};
+  let options = {headers: {'User-Agent': 'angular'}};
+
+  // If a github token is present, use it for authorization.
+  const githubToken = process.env.TOKEN || process.env.GITHUB_TOKEN || '';
+  if (githubToken) {
+    options = {
+      headers: {
+        Authorization: `token ${githubToken}`,
+        ...options.headers,
+      }
+    };
+  }
 
   return new Promise((resolve, reject) => {
     https
@@ -54,9 +70,19 @@ async function requestDataFromGithub(url) {
         .on('error', (e) => { reject(e); });
   });
 }
+// clang-format off
+// clang keeps trying to put the function name on the next line.
+async function getRefsAndShasForTarget(prNumber, suppressLog) {
+  // clang-format on
+  // If the environment variable already contains the refs and shas, reuse them.
+  if (process.env['GITHUB_REFS_AND_SHAS']) {
+    suppressLog ||
+        console.info(`Retrieved refs and SHAs for PR ${prNumber} from environment variables.`);
+    return JSON.parse(process.env['GITHUB_REFS_AND_SHAS']);
+  }
 
-module.exports = async function getRefsAndShasForTarget(prNumber) {
-  console.log(`Getting refs and SHAs for PR ${prNumber} on angular/angular.`);
+  suppressLog ||
+      console.info(`Getting refs and SHAs for PR ${prNumber} on angular/angular from Github.`);
   const pullsUrl = `https://api.github.com/repos/angular/angular/pulls/${prNumber}`;
   const result = await requestDataFromGithub(pullsUrl);
 
@@ -84,6 +110,19 @@ module.exports = async function getRefsAndShasForTarget(prNumber) {
     latestShaOfTargetBranch: latestShaOfTargetBranch.trim(),
     latestShaOfPrBranch: latestShaOfPrBranch.trim(),
   };
-
   return output;
-};
+}
+
+// If the script is called directly, log the output of the refs and sha for the
+// requested PR.
+if (require.main === module) {
+  const run = async() => {
+    const prNumber = Number.parseInt(process.argv[2], 10);
+    if (!!prNumber) {
+      console.info(JSON.stringify(await getRefsAndShasForTarget(prNumber, true)));
+    }
+  };
+  run();
+}
+
+module.exports = getRefsAndShasForTarget;