diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 4ad4d15..c8750b8 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -5,6 +5,10 @@ on:
     branches: [main]
   workflow_dispatch:
 
+concurrency:
+  group: ci-${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   build-and-test:
     name: Build and Test (macOS)
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 94fe838..337bff6 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -39,4 +39,5 @@ Before merging:
 ## CI/CD Scope for Now
 - CI is required.
 - We currently run minimal safety checks (build + `JChatTests` on GitHub Actions).
+- CI cancels stale in-progress runs on the same branch when newer commits are pushed.
 - Full CD/release automation is intentionally deferred.
diff --git a/JChat/Documentation/CHANGELOG_INTERNAL.md b/JChat/Documentation/CHANGELOG_INTERNAL.md
index c39ab17..f4f2f66 100644
--- a/JChat/Documentation/CHANGELOG_INTERNAL.md
+++ b/JChat/Documentation/CHANGELOG_INTERNAL.md
@@ -12,3 +12,4 @@
 - Replaced abrupt setup blocking with a first-run readiness checklist for API key and default model in `ContentView`.
 - Added a canonical manual regression checklist for chat, setup guardrails, markdown, and settings persistence flows.
 - Hardened chat usage accounting by clamping token/cost totals at zero during delete/regenerate paths.
+- Optimized CI with workflow concurrency to auto-cancel stale in-progress runs per branch.