diff --git a/.github/workflows/book.yml b/.github/workflows/book.yml
index b99d7a939..732ff8b66 100644
--- a/.github/workflows/book.yml
+++ b/.github/workflows/book.yml
@@ -35,6 +35,8 @@ permissions:
 # Scope this to the ref, and keep the single-deploy guarantee on the deploy job
 # itself. Superseded PR runs are cancelled; pushes to main are not, so a
 # publish in flight is never interrupted.
+# The group deliberately has no commit SHA. Parallel builds on main would let
+# a slower older commit deploy after a newer one and replace the published site.
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: ${{ github.event_name == 'pull_request' }}
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index a7862db9e..bd0c76495 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -28,9 +28,10 @@ on:
       - 'Cargo.lock'
       - '.github/workflows/**'
 
-# main runs finish; any other ref cancels the older run of this workflow.
+# Each commit on main gets its own group, so it starts at once. Any other ref
+# still shares one group and cancels the older run.
 concurrency:
-  group: ci-gate-${{ github.ref_name }}
+  group: ci-gate-${{ github.ref_name }}${{ github.ref_name == 'main' && format('-{0}', github.sha) || '' }}
   cancel-in-progress: ${{ github.ref_name != 'main' }}
 
 # Every other workflow in the repo pins this rather than inheriting whatever the
diff --git a/.github/workflows/codeql.yml b/.github/workflows/codeql.yml
index afdf30182..60aaba1f3 100644
--- a/.github/workflows/codeql.yml
+++ b/.github/workflows/codeql.yml
@@ -26,9 +26,10 @@ on:
   schedule:
     - cron: "44 3 * * 6"
 
-# main runs finish; any other ref cancels the older run of this workflow.
+# Each commit on main gets its own group, so it starts at once. Any other ref
+# still shares one group and cancels the older run.
 concurrency:
-  group: ${{ github.workflow }}-${{ github.ref_name }}
+  group: ${{ github.workflow }}-${{ github.ref_name }}${{ github.ref_name == 'main' && format('-{0}', github.sha) || '' }}
   cancel-in-progress: ${{ github.ref_name != 'main' }}
 
 jobs:
diff --git a/.github/workflows/cutile-rs.yml b/.github/workflows/cutile-rs.yml
index a853ad584..665ed1429 100644
--- a/.github/workflows/cutile-rs.yml
+++ b/.github/workflows/cutile-rs.yml
@@ -25,9 +25,10 @@ on:
       - "pull-request/[0-9]+"
   workflow_dispatch:
 
-# main runs finish; any other ref cancels the older run of this workflow.
+# Each commit on main gets its own group, so it starts at once. Any other ref
+# still shares one group and cancels the older run.
 concurrency:
-  group: ${{ github.workflow }}-${{ github.ref_name }}
+  group: ${{ github.workflow }}-${{ github.ref_name }}${{ github.ref_name == 'main' && format('-{0}', github.sha) || '' }}
   cancel-in-progress: ${{ github.ref_name != 'main' }}
 
 permissions:
diff --git a/.github/workflows/docs.yml b/.github/workflows/docs.yml
index 98d6da40a..c924c78d7 100644
--- a/.github/workflows/docs.yml
+++ b/.github/workflows/docs.yml
@@ -26,9 +26,10 @@ on:
       - 'Cargo.lock'
       - '.github/workflows/**'
 
-# main runs finish; any other ref cancels the older run of this workflow.
+# Each commit on main gets its own group, so it starts at once. Any other ref
+# still shares one group and cancels the older run.
 concurrency:
-  group: ${{ github.workflow }}-${{ github.ref_name }}
+  group: ${{ github.workflow }}-${{ github.ref_name }}${{ github.ref_name == 'main' && format('-{0}', github.sha) || '' }}
   cancel-in-progress: ${{ github.ref_name != 'main' }}
 
 permissions:
diff --git a/.github/workflows/examples-compile.yml b/.github/workflows/examples-compile.yml
index 9efa9bd73..0f8544cb6 100644
--- a/.github/workflows/examples-compile.yml
+++ b/.github/workflows/examples-compile.yml
@@ -26,9 +26,10 @@ on:
       - 'Cargo.lock'
       - '.github/workflows/**'
 
-# main runs finish; any other ref cancels the older run of this workflow.
+# Each commit on main gets its own group, so it starts at once. Any other ref
+# still shares one group and cancels the older run.
 concurrency:
-  group: ${{ github.workflow }}-${{ github.ref_name }}
+  group: ${{ github.workflow }}-${{ github.ref_name }}${{ github.ref_name == 'main' && format('-{0}', github.sha) || '' }}
   cancel-in-progress: ${{ github.ref_name != 'main' }}
 
 permissions:
diff --git a/.github/workflows/naming-guard.yml b/.github/workflows/naming-guard.yml
index 4f2e9dc4c..00eb30f37 100644
--- a/.github/workflows/naming-guard.yml
+++ b/.github/workflows/naming-guard.yml
@@ -22,9 +22,10 @@ on:
       - 'cuda-oxide/scripts/check-reserved-prefixes.sh'
       - '.github/workflows/naming-guard.yml'
 
-# main runs finish; any other ref cancels the older run of this workflow.
+# Each commit on main gets its own group, so it starts at once. Any other ref
+# still shares one group and cancels the older run.
 concurrency:
-  group: ${{ github.workflow }}-${{ github.ref_name }}
+  group: ${{ github.workflow }}-${{ github.ref_name }}${{ github.ref_name == 'main' && format('-{0}', github.sha) || '' }}
   cancel-in-progress: ${{ github.ref_name != 'main' }}
 
 permissions:
diff --git a/.github/workflows/status-guard.yml b/.github/workflows/status-guard.yml
index 5704006c2..6c7ea3659 100644
--- a/.github/workflows/status-guard.yml
+++ b/.github/workflows/status-guard.yml
@@ -7,9 +7,10 @@ on:
   pull_request:
     branches: [main]
 
-# main runs finish; any other ref cancels the older run of this workflow.
+# Each commit on main gets its own group, so it starts at once. Any other ref
+# still shares one group and cancels the older run.
 concurrency:
-  group: ${{ github.workflow }}-${{ github.ref_name }}
+  group: ${{ github.workflow }}-${{ github.ref_name }}${{ github.ref_name == 'main' && format('-{0}', github.sha) || '' }}
   cancel-in-progress: ${{ github.ref_name != 'main' }}
 
 permissions: