diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2c1665a..2854cd3 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -149,6 +149,36 @@ jobs:
                   output.write(script if script.endswith("\n") else script + "\n")
           PY
 
+      - name: Select prebuilt targets across supported runners
+        run: |
+          set -euo pipefail
+          target_script=("$RUNNER_TEMP"/action-scripts/*-Select-postil-target.sh)
+          [ "${#target_script[@]}" -eq 1 ]
+          fake_bin="$RUNNER_TEMP/fake-target-bin"
+          mkdir -p "$fake_bin"
+          cat >"$fake_bin/uname" <<'SH'
+          #!/usr/bin/env bash
+          set -euo pipefail
+          printf '%s\n' "$FIXTURE_ARCH"
+          SH
+          chmod +x "$fake_bin/uname"
+
+          run_case() {
+            runner_os="$1"
+            architecture="$2"
+            expected="$3"
+            output="$RUNNER_TEMP/target-$runner_os-$architecture.txt"
+            PATH="$fake_bin:$PATH" FIXTURE_ARCH="$architecture" \
+              RUNNER_OS="$runner_os" GITHUB_OUTPUT="$output" \
+              bash "${target_script[0]}"
+            grep -Fx "target=$expected" "$output"
+          }
+
+          run_case Linux x86_64 x86_64-unknown-linux-gnu
+          run_case Linux arm64 aarch64-unknown-linux-gnu
+          run_case macOS x86_64 x86_64-apple-darwin
+          run_case macOS arm64 aarch64-apple-darwin
+
       - name: Reject invalid provider input without exposing credentials
         run: |
           set -euo pipefail
@@ -630,6 +660,10 @@ jobs:
             runner: ubuntu-24.04-arm
           - target: aarch64-unknown-linux-musl
             runner: ubuntu-24.04-arm
+          - target: x86_64-apple-darwin
+            runner: macos-15-intel
+          - target: aarch64-apple-darwin
+            runner: macos-15
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
       - uses: sigstore/cosign-installer@398d4b0eeef1380460a10c8013a76f728fb906ac # v3
@@ -655,7 +689,11 @@ jobs:
           curl -fsSL --retry 3 --retry-connrefused --retry-delay 2 -o "$DEST/postil.tar.gz.pem" "$base/postil-$TARGET.tar.gz.pem"
 
           expected=$(awk '{print $1}' "$DEST/postil.tar.gz.sha256")
-          actual=$(sha256sum "$DEST/postil.tar.gz" | awk '{print $1}')
+          if command -v sha256sum >/dev/null 2>&1; then
+            actual=$(sha256sum "$DEST/postil.tar.gz" | awk '{print $1}')
+          else
+            actual=$(shasum -a 256 "$DEST/postil.tar.gz" | awk '{print $1}')
+          fi
           [ "$expected" = "$actual" ]
 
           cosign verify-blob \
diff --git a/README.md b/README.md
index ea89292..fe73e32 100644
--- a/README.md
+++ b/README.md
@@ -39,7 +39,7 @@ Set the `POSTIL_REVIEW_MODEL` repository variable to a model qualified for your
 | --- | --- | --- |
 | `cli-ref` | yes | Full 40-character `postil-cli` commit SHA |
 | `api-key` | yes | Model provider credential |
-| `cli-release` | no | Matching signed release tag for a prebuilt Linux binary |
+| `cli-release` | no | Matching signed release tag for a prebuilt Linux or macOS binary |
 | `api-base` | no | Model endpoint, defaulting to the CLI provider endpoint |
 | `api-format` | no | `openai-compatible` or `anthropic` |
 | `endpoint-auth-header`, `endpoint-auth-value` | no | Paired additional private-gateway authentication |
diff --git a/action.yml b/action.yml
index 5326188..666d113 100644
--- a/action.yml
+++ b/action.yml
@@ -169,6 +169,11 @@ runs:
             x86_64) target="x86_64-unknown-linux-$libc" ;;
             aarch64|arm64) target="aarch64-unknown-linux-$libc" ;;
           esac
+        elif [ "$RUNNER_OS" = "macOS" ]; then
+          case "$(uname -m)" in
+            x86_64) target="x86_64-apple-darwin" ;;
+            arm64) target="aarch64-apple-darwin" ;;
+          esac
         fi
 
         if [ -n "$target" ]; then
@@ -205,8 +210,6 @@ runs:
           rm -f "$auth_cfg"
           trap - EXIT
           if [ "$tag_sha" = "$CLI_REF" ]; then
-            # Prebuilt artifacts are Linux-only here; other runners fall back
-            # to the source build rather than fetching a binary that cannot run.
             target="$POSTIL_TARGET"
             if [ -n "$target" ]; then
               base="https://github.com/postil-dev/postil-cli/releases/download/$CLI_RELEASE"
@@ -215,7 +218,11 @@ runs:
                  && curl -fsSL --retry 3 --retry-connrefused --retry-delay 2 -o "$DEST/postil.tar.gz.sig" "$base/postil-$target.tar.gz.sig" \
                  && curl -fsSL --retry 3 --retry-connrefused --retry-delay 2 -o "$DEST/postil.tar.gz.pem" "$base/postil-$target.tar.gz.pem"; then
                 expected=$(awk '{print $1}' "$DEST/postil.tar.gz.sha256")
-                actual=$(sha256sum "$DEST/postil.tar.gz" | awk '{print $1}')
+                if command -v sha256sum >/dev/null 2>&1; then
+                  actual=$(sha256sum "$DEST/postil.tar.gz" | awk '{print $1}')
+                else
+                  actual=$(shasum -a 256 "$DEST/postil.tar.gz" | awk '{print $1}')
+                fi
                 # Checksum guards against transit corruption; the checksum file
                 # sits next to the artifact on the same release, so it alone
                 # cannot prove the release wasn't tampered with. The Sigstore