diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f6f964b1..9b7f81cb 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -31,16 +31,39 @@ jobs:
       matrix:
         os: [windows-latest, windows-11-arm, macos-latest, macos-15-intel, ubuntu-latest, ubuntu-22.04, ubuntu-22.04-arm, ubuntu-24.04-arm]
 
+    # TEMPORARY: exercise the c2pa-rs 0.90.0-rc.1 release candidate before it
+    # ships as a release, to surface breaking build issues early. No prebuilt
+    # release binaries exist for the RC, so we build the c2pa_c FFI from source
+    # (C2PA_BUILD_FROM_SOURCE) against a pinned commit instead of downloading the
+    # C2PA_VERSION prebuilt from CMakeLists.txt. Revert this env block and the two
+    # "(TEMPORARY)" steps below once the RC ships and C2PA_VERSION can be bumped.
+    env:
+      C2PA_RS_REF: 66d20c655769b9a46fa87221a996ad5686e0c6f9  # HEAD of branch 0.90.0-rc.1
+      C2PA_BUILD_FROM_SOURCE: "1"
+      C2PA_RS_PATH: ${{ github.workspace }}/c2pa-rs
+
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
 
+      - name: Check out c2pa-rs release candidate (TEMPORARY)
+        uses: actions/checkout@v4
+        with:
+          repository: contentauth/c2pa-rs
+          ref: ${{ env.C2PA_RS_REF }}
+          path: c2pa-rs
+
+      - name: Install Rust toolchain (TEMPORARY - to build the c2pa-rs RC from source)
+        uses: dtolnay/rust-toolchain@stable
+
       - name: Install Ninja (Cmake build generator)
         uses: seanmiddleditch/gha-setup-ninja@master
 
       - name: Setup MSVC toolchain on Windows
-        if: matrix.os == 'windows-latest'
+        if: runner.os == 'Windows'
         uses: ilammy/msvc-dev-cmd@v1
+        with:
+          arch: ${{ matrix.os == 'windows-11-arm' && 'arm64' || 'amd64' }}
 
       - name: Print make version and path
         run: |