diff --git a/.circleci/config.yml b/.circleci/config.yml
deleted file mode 100644
index 4d35c8236d3..00000000000
--- a/.circleci/config.yml
+++ /dev/null
@@ -1,88 +0,0 @@
-version: 2
-
-jobs:
-  analysis:
-    docker:
-      - image: rollupcabal/circleci-node-base:latest
-    steps:
-      - checkout
-      - restore_cache:
-          key: dependency-cache-{{ checksum "package-lock.json" }}
-      - run:
-          name: Installing Dependencies
-          command: npm ci --ignore-scripts
-      - run:
-          name: Running linting
-          command: npm run ci:lint
-      - run:
-          name: Running NPM Security Audit
-          command: npm run security
-      - save_cache:
-          key: dependency-cache-{{ checksum "package-lock.json" }}
-          paths:
-            - ./node_modules
-  node-v10-latest:
-    docker:
-      - image: rollupcabal/circleci-node-v10:latest
-    steps:
-      - checkout
-      - restore_cache:
-          key: dependency-cache-{{ checksum "package-lock.json" }}
-      - run:
-          name: Running tests
-          command: npm run ci:test
-  node-v12-latest:
-    docker:
-      - image: rollupcabal/circleci-node-v12:latest
-    steps:
-      - checkout
-      - restore_cache:
-          key: dependency-cache-{{ checksum "package-lock.json" }}
-      - run:
-          name: Running tests
-          command: npm run ci:test:only
-      - store_artifacts:
-          name: Storing browser build for REPL
-          path: /home/circleci/project/dist/rollup.browser.js
-          destination: rollup.browser.js
-      - run:
-          name: Post REPL comment
-          command: ./scripts/post-comment.js
-  node-v14-latest:
-    docker:
-      - image: rollupcabal/circleci-node-v14:latest
-    steps:
-      - checkout
-      - restore_cache:
-          key: dependency-cache-{{ checksum "package-lock.json" }}
-      - run:
-          name: Running tests with coverage
-          command: npm run ci:coverage
-
-
-workflows:
-  version: 2
-  validate-test:
-    jobs:
-      - analysis:
-          filters:
-            tags:
-              only: /.*/
-      - node-v10-latest:
-          requires:
-            - analysis
-          filters:
-            tags:
-              only: /.*/
-      - node-v12-latest:
-          requires:
-            - analysis
-          filters:
-            tags:
-              only: /.*/
-      - node-v14-latest:
-          requires:
-            - analysis
-          filters:
-            tags:
-              only: /.*/
diff --git a/.github/workflows/node-windows.yml b/.github/workflows/node-windows.yml
deleted file mode 100644
index 786a4b3f323..00000000000
--- a/.github/workflows/node-windows.yml
+++ /dev/null
@@ -1,32 +0,0 @@
-name: Node
-
-on:
-  push:
-    branches:
-      - master
-  pull_request:
-
-jobs:
-  build:
-    runs-on: windows-2019
-
-    strategy:
-      matrix:
-        node: [ '14', '12', '10' ]
-
-    name: ${{ matrix.node }} (Windows)
-    steps:
-      - name: Configure git line-breaks
-        run: git config --global core.autocrlf false
-      - name: Checkout Commit
-        uses: actions/checkout@v1
-      - name: Setup Node
-        uses: actions/setup-node@v1
-        with:
-          node-version: ${{ matrix.node }}
-      - name: Install dependencies
-        run: npm ci --ignore-scripts
-      - name: Run tests
-        run: npm test
-        env:
-          CI: true
diff --git a/.github/workflows/pr-comment.yml b/.github/workflows/pr-comment.yml
deleted file mode 100644
index 3356fef8d49..00000000000
--- a/.github/workflows/pr-comment.yml
+++ /dev/null
@@ -1,35 +0,0 @@
-name: PR Comment
-
-on:
-  pull_request_target:
-
-jobs:
-  comment:
-    runs-on: ubuntu-latest
-    steps:
-      - name: Find Comment
-        uses: peter-evans/find-comment@v1
-        id: fc
-        with:
-          issue-number: ${{ github.event.pull_request.number }}
-          comment-author: 'github-actions[bot]'
-          body-includes: 'Thank you for your contribution!'
-      - name: Create comment
-        if: steps.fc.outputs.comment-id == ''
-        uses: peter-evans/create-or-update-comment@v1
-        with:
-          issue-number: ${{ github.event.pull_request.number }}
-          body: |
-            ### Thank you for your contribution! ❤️
-
-            You can try out this pull request locally by installing Rollup via
-
-            ```bash
-            npm install ${{ github.event.pull_request.head.repo.full_name }}#${{ github.event.pull_request.head.ref }}
-            ```
-
-            Once a build has completed, you can load it into the REPL by inserting the CircleCI build number of the **ci/circleci: node-v12-latest** build into the link below (unfortunately, we cannot auto-update this comment for PRs from forks at this time):
-            ```
-            https://rollupjs.org/repl/?circleci=<build_number>
-            ```
-
diff --git a/.github/workflows/repl-artefacts.yml b/.github/workflows/repl-artefacts.yml
new file mode 100644
index 00000000000..bb301df1418
--- /dev/null
+++ b/.github/workflows/repl-artefacts.yml
@@ -0,0 +1,66 @@
+name: Upload REPL artefacts
+
+on:
+  pull_request_target:
+
+jobs:
+  upload:
+    runs-on: ubuntu-latest
+    name: Upload
+    steps:
+      - name: Checkout Commit
+        uses: actions/checkout@v2
+      - name: Setup Node
+        uses: actions/setup-node@v2
+        with:
+          node-version: 14
+      - name: Install dependencies
+        run: npm ci --ignore-scripts
+      - name: Build artefacts
+        run: npm run build:cjs && npm run build:bootstrap
+      - name: Upload "${{ github.event.pull_request.number }}/rollup.browser.js" to bucket
+        uses: zdurham/s3-upload-github-action@master
+        with:
+          args: --cache-control max-age=300,public
+        env:
+          FILE: dist/rollup.browser.js
+          AWS_REGION: ${{ secrets.AWS_REGION }}
+          S3_BUCKET: ${{ secrets.AWS_S3_BUCKET }}
+          S3_KEY: ${{ github.event.pull_request.number }}/rollup.browser.js
+          AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}
+          AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
+      - name: Upload "${{ github.event.pull_request.number }}/rollup.browser.js.map" to bucket
+        uses: zdurham/s3-upload-github-action@master
+        with:
+          args: --cache-control max-age=300,public
+        env:
+          FILE: dist/rollup.browser.js.map
+          AWS_REGION: ${{ secrets.AWS_REGION }}
+          S3_BUCKET: ${{ secrets.AWS_S3_BUCKET }}
+          S3_KEY: ${{ github.event.pull_request.number }}/rollup.browser.js.map
+          AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}
+          AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
+      - name: Find Comment
+        uses: peter-evans/find-comment@v1
+        id: fc
+        with:
+          issue-number: ${{ github.event.pull_request.number }}
+          comment-author: 'github-actions[bot]'
+          body-includes: 'Thank you for your contribution!'
+      - name: Create or update comment
+        uses: peter-evans/create-or-update-comment@v1
+        with:
+          comment-id: ${{ steps.fc.outputs.comment-id }}
+          issue-number: ${{ github.event.pull_request.number }}
+          edit-mode: replace
+          body: |
+            ### Thank you for your contribution! ❤️
+
+            You can try out this pull request locally by installing Rollup via
+
+            ```bash
+            npm install ${{ github.event.pull_request.head.repo.full_name }}#${{ github.event.pull_request.head.ref }}
+            ```
+
+            or load it into the REPL:
+            https://rollupjs.org/repl/?pr=${{ github.event.pull_request.number }}
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
new file mode 100644
index 00000000000..5207d68510e
--- /dev/null
+++ b/.github/workflows/tests.yml
@@ -0,0 +1,93 @@
+name: Tests
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+
+jobs:
+  linux14:
+    runs-on: ubuntu-latest
+    name: Node 14 + Coverage (Linux)
+    steps:
+      - name: Checkout Commit
+        uses: actions/checkout@v2
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
+      - name: Setup Node
+        uses: actions/setup-node@v2
+        with:
+          node-version: '14'
+      - name: Install dependencies
+        run: npm ci --ignore-scripts
+      - name: Run tests with coverage
+        run: npm run ci:coverage
+        env:
+          CI: true
+
+  linux12:
+    runs-on: ubuntu-latest
+    name: Node 12 + Extra Tests (Linux)
+    steps:
+      - name: Checkout Commit
+        uses: actions/checkout@v2
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
+      - name: Setup Node
+        uses: actions/setup-node@v2
+        with:
+          node-version: '12'
+      - name: Install dependencies
+        run: npm ci --ignore-scripts
+      - name: Lint
+        run: npm run ci:lint
+      - name: Vulnerabilities
+        run: npm run security
+      - name: Run all tests
+        run: npm run ci:test
+        env:
+          CI: true
+
+  linux10:
+    runs-on: ubuntu-latest
+    name: Node 10 (Linux)
+    steps:
+      - name: Checkout Commit
+        uses: actions/checkout@v2
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
+      - name: Setup Node
+        uses: actions/setup-node@v2
+        with:
+          node-version: '10'
+      - name: Install dependencies
+        run: npm ci --ignore-scripts
+      - name: Run tests
+        run: npm run ci:test:only
+        env:
+          CI: true
+
+  windows:
+    runs-on: windows-2019
+    strategy:
+      matrix:
+        node: ['14', '12', '10']
+    name: Node ${{ matrix.node }} (Windows)
+    steps:
+      - name: Configure git line-breaks
+        run: git config --global core.autocrlf false
+      - name: Checkout Commit
+        uses: actions/checkout@v2
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
+      - name: Setup Node
+        uses: actions/setup-node@v2
+        with:
+          node-version: ${{ matrix.node }}
+      - name: Install dependencies
+        run: npm ci --ignore-scripts
+      - name: Run tests
+        run: npm test
+        env:
+          CI: true
diff --git a/scripts/post-comment.js b/scripts/post-comment.js
deleted file mode 100755
index 2e29de90ae0..00000000000
--- a/scripts/post-comment.js
+++ /dev/null
@@ -1,61 +0,0 @@
-#!/usr/bin/env node
-
-const path = require('path');
-const fetch = require('node-fetch');
-
-const authToken = process.env.GH_AUTH_TOKEN;
-if (!authToken) {
-	console.log('Could not find auth token.');
-	process.exit(0);
-}
-
-const prNumber = path.basename(
-	process.env.CIRCLE_PULL_REQUEST || process.env.CI_PULL_REQUEST || ''
-);
-if (!prNumber) {
-	console.log('No pull request number found');
-	process.exit(0);
-}
-
-const headline = '### Thank you for your contribution! ❤️';
-
-postComment();
-
-async function postComment() {
-	const existingId = await findExistingComment();
-	console.log(existingId ? `Update comment ${existingId}` : 'Create new comment.');
-	const installPath = await getInstallPath();
-	const path = existingId ? `issues/comments/${existingId}` : `issues/${prNumber}/comments`;
-	const method = existingId ? 'PATCH' : 'POST';
-	await fetch(getApiUrl(path), {
-		method,
-		body: JSON.stringify({
-			body: `${headline}
-
-You can try out this pull request locally by installing Rollup via
-
-\`\`\`
-npm install ${installPath}
-\`\`\`
-
-or load it into the REPL:
-https://rollupjs.org/repl/?circleci=${process.env.CIRCLE_BUILD_NUM}
-`
-		})
-	});
-}
-
-async function findExistingComment() {
-	const comments = await (await fetch(getApiUrl(`issues/${prNumber}/comments`), {})).json();
-	const existingComment = comments.find(comment => comment.body.startsWith(headline));
-	return existingComment && existingComment.id;
-}
-
-async function getInstallPath() {
-	const prInfo = await (await fetch(getApiUrl(`pulls/${prNumber}`), {})).json();
-	return `${prInfo.head.repo.full_name}#${prInfo.head.ref}`;
-}
-
-function getApiUrl(path) {
-	return `https://${authToken}:x-oauth-basic@api.github.com/repos/rollup/rollup/${path}`;
-}