diff --git a/.github/workflows/draft-pdf.yml b/.github/workflows/draft-pdf.yml
index 566f1232..a43ecc8d 100644
--- a/.github/workflows/draft-pdf.yml
+++ b/.github/workflows/draft-pdf.yml
@@ -10,6 +10,10 @@ on:
       - paper.bib
       - architecture.png
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.run_id }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
 jobs:
   paper:
     runs-on: ubuntu-latest
diff --git a/.github/workflows/pr_code_changes.yaml b/.github/workflows/pr_code_changes.yaml
index 978c13cb..c63cd69b 100644
--- a/.github/workflows/pr_code_changes.yaml
+++ b/.github/workflows/pr_code_changes.yaml
@@ -14,6 +14,10 @@ on:
       - src/policyengine/data/bundle/manifest.json
   workflow_dispatch:
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.run_id }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
 jobs:
   check-changelog:
     name: Check changelog fragment
@@ -127,7 +131,7 @@ jobs:
       - name: Verify bundle packages
         run: policyengine bundle verify --country us --country uk --packages-only --json
   Test:
-    runs-on: macos-latest
+    runs-on: ubuntu-latest
     strategy:
       fail-fast: false
       matrix:
diff --git a/.github/workflows/pr_docs_changes.yaml b/.github/workflows/pr_docs_changes.yaml
index 9e70a97a..d3f090c4 100644
--- a/.github/workflows/pr_docs_changes.yaml
+++ b/.github/workflows/pr_docs_changes.yaml
@@ -11,6 +11,10 @@ on:
       - .github/**
   workflow_dispatch:
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.run_id }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
 jobs:
   Test:
     runs-on: ubuntu-latest
diff --git a/.github/workflows/push.yaml b/.github/workflows/push.yaml
index c12509a2..781a2f3e 100644
--- a/.github/workflows/push.yaml
+++ b/.github/workflows/push.yaml
@@ -39,7 +39,7 @@ jobs:
 
   Test:
     if: github.event.head_commit.message != 'Update package version'
-    runs-on: macos-latest
+    runs-on: ubuntu-latest
     strategy:
       fail-fast: false
       matrix:
diff --git a/changelog.d/545.changed.md b/changelog.d/545.changed.md
new file mode 100644
index 00000000..afd0a414
--- /dev/null
+++ b/changelog.d/545.changed.md
@@ -0,0 +1 @@
+Run the full Python test matrices on GitHub-hosted Ubuntu machines and cancel earlier workflow runs when a pull request receives a new commit.