diff --git a/.github/workflows/clang_sanitizers.yml b/.github/workflows/clang_sanitizers.yml
index ef005cbbc72..8efcdc9a431 100644
--- a/.github/workflows/clang_sanitizers.yml
+++ b/.github/workflows/clang_sanitizers.yml
@@ -160,18 +160,3 @@ jobs:
         ulimit -c unlimited
 
         mpirun -n 2 ../../../build_EB/bin/warpx.2d inputs_2d warpx.serialize_initial_conditions = 0
-
-  save_pr_number:
-    if: github.event_name == 'pull_request'
-    runs-on: ubuntu-latest
-    steps:
-      - name: Save PR number
-        env:
-          PR_NUMBER: ${{ github.event.number }}
-        run: |
-          echo $PR_NUMBER > pr_number.txt
-      - uses: actions/upload-artifact@v4
-        with:
-          name: pr_number
-          path: pr_number.txt
-          retention-days: 1
diff --git a/.github/workflows/clang_tidy.yml b/.github/workflows/clang_tidy.yml
index 96c7337a3f2..5a4f83f01f1 100644
--- a/.github/workflows/clang_tidy.yml
+++ b/.github/workflows/clang_tidy.yml
@@ -60,18 +60,3 @@ jobs:
 
         ccache -s
         du -hs ~/.cache/ccache
-
-  save_pr_number:
-    if: github.event_name == 'pull_request'
-    runs-on: ubuntu-latest
-    steps:
-      - name: Save PR number
-        env:
-          PR_NUMBER: ${{ github.event.number }}
-        run: |
-          echo $PR_NUMBER > pr_number.txt
-      - uses: actions/upload-artifact@v4
-        with:
-          name: pr_number
-          path: pr_number.txt
-          retention-days: 1
diff --git a/.github/workflows/cleanup-cache-postpr.yml b/.github/workflows/cleanup-cache-postpr.yml
index 9a2ffb0f61a..5e9a70cd5a4 100644
--- a/.github/workflows/cleanup-cache-postpr.yml
+++ b/.github/workflows/cleanup-cache-postpr.yml
@@ -23,8 +23,11 @@ jobs:
 
           REPO=${{ github.repository }}
 
-          gh run download ${{ github.event.workflow_run.id }} -n pr_number
-          pr_number=`cat pr_number.txt`
+          # For debugging cat ${GITHUB_EVENT_PATH} to see the payload.
+
+          pr_head_sha=${{ github.event.workflow_run.head_sha }}
+          pr_number=$(gh pr list --state all --search $pr_head_sha --json number --jq '.[0].number')
+          echo "Post-PR cache cleanup for PR ${pr_number}"
           BRANCH=refs/pull/${pr_number}/merge
 
           # Setting this to not fail the workflow while deleting cache keys.
diff --git a/.github/workflows/cleanup-cache.yml b/.github/workflows/cleanup-cache.yml
index bd1a518acf4..3abe232b879 100644
--- a/.github/workflows/cleanup-cache.yml
+++ b/.github/workflows/cleanup-cache.yml
@@ -29,9 +29,12 @@ jobs:
           # Triggering workflow run name (e.g., LinuxClang)
           WORKFLOW_NAME="${{ github.event.workflow_run.name }}"
 
+          # For debugging, cat ${GITHUB_EVENT_PATH} to see the payload.
+
           if [[ $EVENT == "pull_request" ]]; then
-            gh run download ${{ github.event.workflow_run.id }} -n pr_number
-            pr_number=`cat pr_number.txt`
+            pr_head_sha=${{ github.event.workflow_run.head_sha }}
+            pr_number=$(gh pr list --search $pr_head_sha --json number --jq '.[0].number')
+            echo "Clean up cache for PR ${pr_number}"
             BRANCH=refs/pull/${pr_number}/merge
           else
             BRANCH=refs/heads/${{ github.event.workflow_run.head_branch }}
@@ -54,6 +57,7 @@ jobs:
           IFS=$'\n'
           for j in $cached_jobs
           do
+            # Delete all entries except the last used one
             old_keys=$(gh actions-cache list -L 100 -R $REPO -B $BRANCH --key "${j}-git-" --sort last-used | cut -f 1 | tail -n +2)
             for k in $old_keys
             do
diff --git a/.github/workflows/codeql.yml b/.github/workflows/codeql.yml
index bc0bee545cc..5c36b9d9f21 100644
--- a/.github/workflows/codeql.yml
+++ b/.github/workflows/codeql.yml
@@ -110,18 +110,3 @@ jobs:
         uses: github/codeql-action/upload-sarif@v3
         with:
           sarif_file: sarif-results/${{ matrix.language }}.sarif
-
-  save_pr_number:
-    if: github.event_name == 'pull_request'
-    runs-on: ubuntu-latest
-    steps:
-      - name: Save PR number
-        env:
-          PR_NUMBER: ${{ github.event.number }}
-        run: |
-          echo $PR_NUMBER > pr_number.txt
-      - uses: actions/upload-artifact@v4
-        with:
-          name: pr_number
-          path: pr_number.txt
-          retention-days: 1
diff --git a/.github/workflows/cuda.yml b/.github/workflows/cuda.yml
index 9554e1faa3a..010ce8090ac 100644
--- a/.github/workflows/cuda.yml
+++ b/.github/workflows/cuda.yml
@@ -203,18 +203,3 @@ jobs:
 
         ccache -s
         du -hs ~/.cache/ccache
-
-  save_pr_number:
-    if: github.event_name == 'pull_request'
-    runs-on: ubuntu-latest
-    steps:
-      - name: Save PR number
-        env:
-          PR_NUMBER: ${{ github.event.number }}
-        run: |
-          echo $PR_NUMBER > pr_number.txt
-      - uses: actions/upload-artifact@v4
-        with:
-          name: pr_number
-          path: pr_number.txt
-          retention-days: 1
diff --git a/.github/workflows/hip.yml b/.github/workflows/hip.yml
index 8b89e3dc4d0..ba537e776d4 100644
--- a/.github/workflows/hip.yml
+++ b/.github/workflows/hip.yml
@@ -127,18 +127,3 @@ jobs:
 
         ccache -s
         du -hs ~/.cache/ccache
-
-  save_pr_number:
-    if: github.event_name == 'pull_request'
-    runs-on: ubuntu-latest
-    steps:
-      - name: Save PR number
-        env:
-          PR_NUMBER: ${{ github.event.number }}
-        run: |
-          echo $PR_NUMBER > pr_number.txt
-      - uses: actions/upload-artifact@v4
-        with:
-          name: pr_number
-          path: pr_number.txt
-          retention-days: 1
diff --git a/.github/workflows/intel.yml b/.github/workflows/intel.yml
index 8a7867fcbc8..485a5229c6a 100644
--- a/.github/workflows/intel.yml
+++ b/.github/workflows/intel.yml
@@ -194,18 +194,3 @@ jobs:
      #   python3 -m pip install --upgrade build packaging setuptools wheel
      #   PYWARPX_LIB_DIR=$PWD/build_sp/lib/site-packages/pywarpx/ python3 -m pip wheel .
      #   python3 -m pip install *.whl
-
-  save_pr_number:
-    if: github.event_name == 'pull_request'
-    runs-on: ubuntu-latest
-    steps:
-      - name: Save PR number
-        env:
-          PR_NUMBER: ${{ github.event.number }}
-        run: |
-          echo $PR_NUMBER > pr_number.txt
-      - uses: actions/upload-artifact@v4
-        with:
-          name: pr_number
-          path: pr_number.txt
-          retention-days: 1
diff --git a/.github/workflows/macos.yml b/.github/workflows/macos.yml
index dfd32f459f0..124d26fa7f7 100644
--- a/.github/workflows/macos.yml
+++ b/.github/workflows/macos.yml
@@ -85,18 +85,3 @@ jobs:
         export OMP_NUM_THREADS=1
 
         mpirun -n 2 Examples/Physics_applications/laser_acceleration/PICMI_inputs_3d.py
-
-  save_pr_number:
-    if: github.event_name == 'pull_request'
-    runs-on: ubuntu-latest
-    steps:
-      - name: Save PR number
-        env:
-          PR_NUMBER: ${{ github.event.number }}
-        run: |
-          echo $PR_NUMBER > pr_number.txt
-      - uses: actions/upload-artifact@v4
-        with:
-          name: pr_number
-          path: pr_number.txt
-          retention-days: 1
diff --git a/.github/workflows/post-pr.yml b/.github/workflows/post-pr.yml
index 2768ef376cc..5f0b1534970 100644
--- a/.github/workflows/post-pr.yml
+++ b/.github/workflows/post-pr.yml
@@ -4,17 +4,13 @@ on:
     types:
       - closed
 
+# This workflow does not have the permission to clean up cache for PRs
+# originated from a fork. The purpose here is to trigger a workflow_run
+# cleanup-cache-postpr.yml that has the right permission.
+
 jobs:
-  cleanup:
+  noop:
     runs-on: ubuntu-latest
     steps:
-      - name: Save PR number
-        env:
-          PR_NUMBER: ${{ github.event.number }}
-        run: |
-          echo $PR_NUMBER > pr_number.txt
-      - uses: actions/upload-artifact@v4
-        with:
-          name: pr_number
-          path: pr_number.txt
-          retention-days: 1
+      - name: No OP
+        run: echo "This workflow is going to trigger CleanUpCachePostPR."
diff --git a/.github/workflows/ubuntu.yml b/.github/workflows/ubuntu.yml
index 05e53883534..bf6652e9c69 100644
--- a/.github/workflows/ubuntu.yml
+++ b/.github/workflows/ubuntu.yml
@@ -223,18 +223,3 @@ jobs:
       run: |
         export OMP_NUM_THREADS=1
         mpirun -n 2 Examples/Physics_applications/laser_acceleration/PICMI_inputs_3d.py
-
-  save_pr_number:
-    if: github.event_name == 'pull_request'
-    runs-on: ubuntu-latest
-    steps:
-      - name: Save PR number
-        env:
-          PR_NUMBER: ${{ github.event.number }}
-        run: |
-          echo $PR_NUMBER > pr_number.txt
-      - uses: actions/upload-artifact@v4
-        with:
-          name: pr_number
-          path: pr_number.txt
-          retention-days: 1