diff --git a/.github/workflows/pull_request.yml b/.github/workflows/pull_request.yml
index 3be4e8fdc..c5d2d638a 100644
--- a/.github/workflows/pull_request.yml
+++ b/.github/workflows/pull_request.yml
@@ -7,6 +7,10 @@ on:
   pull_request:
     types: [opened, reopened, synchronize]
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   soundness:
     uses: swiftlang/github-workflows/.github/workflows/soundness.yml@main
@@ -49,7 +53,7 @@ jobs:
     strategy:
       fail-fast: true
       matrix:
-        swift_version: ['6.2', '6.3', 'nightly']
+        swift_version: ['6.3', 'nightly']
         os_version: ['jammy']
         jdk_vendor: ['corretto']
     container:
@@ -75,7 +79,7 @@ jobs:
     strategy:
       fail-fast: true
       matrix:
-        swift_version: ['6.2', '6.3']
+        swift_version: ['6.3']
         os_version: ['macos']
         jdk_vendor: ['corretto']
     env:
@@ -143,7 +147,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        swift_version: ['6.1.3', '6.2', '6.3', 'nightly']
+        swift_version: ['6.1.3', '6.3', 'nightly']
         os_version: ['jammy']
         jdk_vendor: ['corretto']
     container:
@@ -167,7 +171,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        swift_version: ['6.2.3', '6.3']
+        swift_version: ['6.3']
         os_version: ['macos']
         jdk_vendor: ['corretto']
     env:
@@ -221,7 +225,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        swift_version: ['6.1.3', '6.2', '6.3', 'nightly']
+        swift_version: ['6.3']
         os_version: ['jammy']
         jdk_vendor: ['corretto']
         sample_app: [  # TODO: use a reusable-workflow to generate those names
@@ -239,6 +243,15 @@ jobs:
       - uses: actions/checkout@v6
       - name: Prepare CI Environment
         uses: ./.github/actions/prepare_env
+      - name: Cache sample .build
+        uses: actions/cache@v4
+        continue-on-error: true
+        with:
+          path: Samples/${{ matrix.sample_app }}/.build
+          key: ${{ runner.os }}-swift${{ matrix.swift_version }}-sample-${{ matrix.sample_app }}-${{ hashFiles('Sources/**/*.swift', 'Plugins/**/*.swift', 'Package.swift', 'Package.resolved') }}
+          restore-keys: |
+            ${{ runner.os }}-swift${{ matrix.swift_version }}-sample-${{ matrix.sample_app }}-
+            ${{ runner.os }}-swift${{ matrix.swift_version }}-sample-
       - name: "Verify sample: ${{ matrix.sample_app }}"
         run: .github/scripts/validate_sample.sh Samples/${{ matrix.sample_app }}
 
@@ -249,7 +262,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        swift_version: ['6.2', '6.3']  # no nightly testing on macOS
+        swift_version: ['6.3']  # no nightly testing on macOS
         os_version: ['macos']
         jdk_vendor: ['corretto']
         sample_app: [  # TODO: use a reusable-workflow to generate those names
@@ -269,6 +282,15 @@ jobs:
         run: ./.github/scripts/install_swiftly.sh
         env:
           SWIFT_VERSION: "${{ matrix.swift_version }}"
+      - name: Cache sample .build
+        uses: actions/cache@v4
+        continue-on-error: true
+        with:
+          path: Samples/${{ matrix.sample_app }}/.build
+          key: ${{ runner.os }}-swift${{ matrix.swift_version }}-sample-${{ matrix.sample_app }}-${{ hashFiles('Sources/**/*.swift', 'Plugins/**/*.swift', 'Package.swift', 'Package.resolved') }}
+          restore-keys: |
+            ${{ runner.os }}-swift${{ matrix.swift_version }}-sample-${{ matrix.sample_app }}-
+            ${{ runner.os }}-swift${{ matrix.swift_version }}-sample-
       - name: "Verify sample ${{ matrix.sample_app }}"
         run: .github/scripts/validate_sample.sh Samples/${{ matrix.sample_app }}