diff --git a/.github/downstream-project/Package.swift b/.github/downstream-project/Package.swift
new file mode 100644
index 000000000..dfa869459
--- /dev/null
+++ b/.github/downstream-project/Package.swift
@@ -0,0 +1,25 @@
+// swift-tools-version: 6.3
+
+import PackageDescription
+
+let package = Package(
+    name: "OpenAPIKit-Project",
+    platforms: [
+        .macOS("26.4")
+    ],
+    products: [
+        .executable(name: "OpenAPIKit-Project", targets: ["OpenAPIKit-Project"])
+    ],
+    dependencies: [
+        .package(path: "../../")
+    ],
+    targets: [
+        .executableTarget(
+            name: "OpenAPIKit-Project",
+            dependencies: [
+                .product(name: "OpenAPIKit", package: "OpenAPIKit")
+            ]
+        )
+    ],
+    swiftLanguageModes: [.v6]
+)
diff --git a/.github/downstream-project/Sources/Main.swift b/.github/downstream-project/Sources/Main.swift
new file mode 100644
index 000000000..8cb8aa198
--- /dev/null
+++ b/.github/downstream-project/Sources/Main.swift
@@ -0,0 +1,3 @@
+import OpenAPIKit
+
+print("Hello World!")
\ No newline at end of file
diff --git a/.github/workflows/codecov.yml b/.github/workflows/codecov.yml
index 709425554..5c5832c83 100644
--- a/.github/workflows/codecov.yml
+++ b/.github/workflows/codecov.yml
@@ -1,6 +1,7 @@
 name: Code Coverage
 
-on: [pull_request]
+on:
+  pull_request:
 
 jobs:
   codecov:
diff --git a/.github/workflows/downstream-project.yml b/.github/workflows/downstream-project.yml
new file mode 100644
index 000000000..bf20e35da
--- /dev/null
+++ b/.github/workflows/downstream-project.yml
@@ -0,0 +1,25 @@
+name: Downstream Project
+
+on:
+  pull_request:
+
+jobs:
+  build-with-compiler-flags:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        image:
+          - swift:6.3-noble
+          - swiftlang/swift:nightly-noble
+        flags:
+          - []
+          - ['-Xswiftc', '-cross-module-optimization']
+    container: ${{ matrix.image }}
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v5
+    - name: Build Downstream Project
+      run: |
+        cd .github/downstream-project
+        swift build -c release ${{ join(matrix.flags, ' ') }}
diff --git a/.github/workflows/traits.yml b/.github/workflows/traits.yml
index 6a89e3c4a..019d4c845 100644
--- a/.github/workflows/traits.yml
+++ b/.github/workflows/traits.yml
@@ -1,6 +1,7 @@
 name: Traits
 
-on: [pull_request]
+on:
+  pull_request:
 
 jobs:
   without-default-traits: