diff --git a/.github/backwards-compatibility-check.sh b/.github/backwards-compatibility-check.sh
new file mode 100644
index 00000000000..9467e36a295
--- /dev/null
+++ b/.github/backwards-compatibility-check.sh
@@ -0,0 +1,133 @@
+#!/bin/bash
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -e
+
+# USAGE:
+#
+#     backwards-compatibility-check.sh COMPONENT [BASE_REF]
+#
+# COMPONENT: The component directory name to run the backwards compatibility check for.
+# BASE_REF: Optional. The baseline git ref (e.g. 'main', 'origin/main' or a release tag) to compare against. Defaults to 'main'.
+
+if [ "$#" -lt 1 ] || [ "$#" -gt 2 ]; then
+    echo "usage: backwards-compatibility-check.sh COMPONENT [BASE_REF]"
+    exit 1
+fi
+
+COMPONENT=$1
+BASE_REF=${2:-main}
+
+# Exception for 'dev'
+if [ "${COMPONENT}" = "dev" ]; then
+    echo "Skipping dev directory (not a public component)."
+    exit 0
+fi
+
+# Check if component directory exists
+if [ ! -d "${COMPONENT}" ]; then
+    echo "Error: Directory ${COMPONENT} does not exist!" >&2
+    exit 1
+fi
+
+# Check if composer.json exists
+COMP_JSON="${COMPONENT}/composer.json"
+if [ ! -f "${COMP_JSON}" ]; then
+    echo "Error: composer.json not found in ${COMPONENT}!" >&2
+    exit 1
+fi
+
+echo "Checking backwards compatibility for component: ${COMPONENT} against baseline: ${BASE_REF}" >&2
+
+# Check if the component existed in the baseline reference
+if ! git rev-parse --verify "${BASE_REF}:${COMPONENT}" >/dev/null 2>&1; then
+    echo "Component ${COMPONENT} did not exist in baseline ${BASE_REF}. Skipping check (all additions)." >&2
+    exit 0
+fi
+
+# Create a temporary directory
+TMP_DIR=$(mktemp -d)
+
+# Initialize a dummy git repo inside TMP_DIR so roave-backward-compatibility-check can compare revisions
+(
+    cd "${TMP_DIR}"
+    git init -q
+)
+
+# Extract baseline files from the BASE_REF, stripping the prefix folder so they land at the root of TMP_DIR
+if ! git archive "${BASE_REF}" "${COMPONENT}" | tar -x --strip-components=1 -C "${TMP_DIR}" 2>/dev/null; then
+    echo "Error: Failed to archive and extract files for ${COMPONENT} from git ref ${BASE_REF}." >&2
+    rm -rf "${TMP_DIR}"
+    exit 1
+fi
+
+(
+    cd "${TMP_DIR}"
+    git add -A
+    git commit -q -m "Base state from ${BASE_REF}"
+)
+
+# Copy the current local component files over the baseline repository,
+# making sure to exclude vendor directories or composer-local files.
+echo "Applying local changes from ${COMPONENT} to the baseline clone..." >&2
+rsync -a --exclude="vendor/" --exclude="composer-local.json" "${COMPONENT}/" "${TMP_DIR}/"
+
+# Commit the changes in the cloned split repository so we can compare them
+CODE=0
+if (
+    cd "${TMP_DIR}"
+    git add -A
+
+    # Check if there are any changes to commit
+    if ! git diff --cached --quiet; then
+        git commit -q -m "Apply local PR changes"
+        echo "Running Roave Backward Compatibility Check..." >&2
+
+        # Locate the roave binary portably
+        COMPOSER_BIN=$(composer global config bin-dir --absolute 2>/dev/null || echo ~/.composer/vendor/bin)
+        ROAVE_BIN=$(command -v roave-backward-compatibility-check || echo "${COMPOSER_BIN}/roave-backward-compatibility-check")
+
+        FORMAT=${BC_FORMAT:-markdown}
+        if [ "${FORMAT}" = "markdown" ]; then
+            # Run Roave check and capture output
+            OUTPUT=$("${ROAVE_BIN}" --from=HEAD~1 --format=markdown 2>/dev/null || true)
+            if [ -n "${OUTPUT}" ]; then
+                echo "<details>"
+                echo "<summary><b>${COMPONENT}</b>: Backwards Compatibility Breaks Detected</summary>"
+                echo ""
+                echo "${OUTPUT}"
+                echo "</details>"
+                echo ""
+                exit 1
+            fi
+        else
+            if ! "${ROAVE_BIN}" --from=HEAD~1 --format="${FORMAT}"; then
+                echo "❌ BC Breaks detected in ${COMPONENT}!" >&2
+                exit 1
+            else
+                echo "✅ No BC Breaks detected in ${COMPONENT}." >&2
+            fi
+        fi
+    else
+        echo "No files modified for ${COMPONENT} compared to ${BASE_REF}. Skipping check." >&2
+    fi
+); then
+    CODE=0
+else
+    CODE=1
+fi
+
+rm -rf "${TMP_DIR}"
+exit $CODE
diff --git a/.github/workflows/release-checks.yaml b/.github/workflows/release-checks.yaml
index 336a93531f5..0d1a14b5edc 100644
--- a/.github/workflows/release-checks.yaml
+++ b/.github/workflows/release-checks.yaml
@@ -5,6 +5,7 @@ on:
     branches: ['main']
 permissions:
   contents: read
+  pull-requests: write
 jobs:
   # More info at https://github.com/Roave/BackwardCompatibilityCheck.
   backwards-compatibility-check:
@@ -19,28 +20,8 @@ jobs:
         uses: shivammathur/setup-php@v2
         with:
           php-version: "8.1"
-      - name: "Rebase PR branch onto main branch"
-        if: github.event.pull_request.user.login != 'release-please[bot]'
-        run: |
-          git config user.name "Github Actions"
-          git config user.email "actions@github.com"
-          git checkout ${{ github.event.pull_request.head.sha }}
-          if ! git rebase origin/main; then
-            echo "Failed to rebase PR branch onto main. There may be conflicts. Please resolve conflicts or rebase manually."
-            exit 1
-          fi
       - name: "Install dependencies"
         run: composer global require "roave/backward-compatibility-check:^8.2"
-      - name: "Check for BC breaks"
-        if: github.event.pull_request.user.login != 'release-please[bot]'
-        run: |
-          ~/.composer/vendor/bin/roave-backward-compatibility-check --from=origin/main --format=github-actions
-      - name: "Check for BC label"
-        run: |
-          if [[ "true" == "${{ contains(github.event.pull_request.title, '!:') }}" ]]; then
-            echo "Breaking change label found in PR title"
-            exit 1
-          fi
       - name: Get Latest Release
         if: github.event.pull_request.user.login == 'release-please[bot]'
         id: latest-release
@@ -48,14 +29,58 @@ jobs:
         with:
           repository: ${{ github.repository }}
           token: ${{ secrets.GITHUB_TOKEN }}
-      - name: "Check for BC breaks (Next Release)"
-        if: github.event.pull_request.user.login == 'release-please[bot]'
-        # We've already approved and justified the breaking changes. Run the check but continue on error
-        continue-on-error: true
+      - name: "Check for BC breaks"
+        id: check-bc
         run: |
-          ~/.composer/vendor/bin/roave-backward-compatibility-check \
-              --from=${{ steps.latest-release.outputs.release }} \
-              --to=origin/main --format=github-actions
+          git config --global user.name "Github Actions"
+          git config --global user.email "actions@github.com"
+
+          # Determine base ref for git diff
+          BASE_REF="${{ steps.latest-release.outputs.release }}"
+          BASE_REF=${BASE_REF:-origin/main}
+
+          # Find changed component directories
+          CHANGED_COMPONENTS=$(git diff ${BASE_REF} --name-only | grep -E '^[A-Z][a-zA-Z0-9]*/' | cut -d'/' -f1 | sort -u || true)
+          if [ -z "${CHANGED_COMPONENTS}" ]; then
+            echo "No public component directories have changed."
+            exit 0
+          fi
+
+          IS_RELEASE_PR="${{ github.event.pull_request.user.login == 'release-please[bot]' }}"
+
+          if [ "${IS_RELEASE_PR}" = "true" ]; then
+            # Release PR: gather markdown and do not fail the step
+            BC_BREAKS=""
+            for COMPONENT in ${CHANGED_COMPONENTS}; do
+              BC_BREAKS="$BC_BREAKS$(BC_FORMAT="markdown" bash .github/backwards-compatibility-check.sh "${COMPONENT}" "${BASE_REF}" || true)"
+            done
+            printf "bc-breaks<<EOF\n%s\nEOF\n" "$BC_BREAKS" >> $GITHUB_OUTPUT
+          else
+            # Normal PR: use github-actions format and fail if there are breaks
+            FAIL=""
+            for COMPONENT in ${CHANGED_COMPONENTS}; do
+              if ! BC_FORMAT="github-actions" bash .github/backwards-compatibility-check.sh "${COMPONENT}" "${BASE_REF}"; then
+                FAIL="true"
+              fi
+            done
+
+            if [ "${FAIL}" = "true" ]; then
+              exit 1
+            elif [[ "true" == "${{ contains(github.event.pull_request.title, '!:') }}" ]]; then
+              echo "❌ Error: You indicated breaking changes in your PR title (!:), but no backwards compatibility breaks were detected by the automated check."
+              exit 1
+            fi
+          fi
+      - name: "Add or update PR comment with BC breaks for Release PRs"
+        if: github.event.pull_request.user.login == 'release-please[bot]' && steps.check-bc.outputs.bc-breaks != ''
+        uses: marocchino/sticky-pull-request-comment@v2
+        with:
+          header: bc-breaking-changes-comment
+          message: |
+            ## ⚠️ Backwards Compatibility (BC) Breaking Changes Notice
+            This PR contains backward compatibility breaking changes detected by the automated BC check against the latest release. Please review the details below:
+
+            ${{ steps.check-bc.outputs.bc-breaks }}
 
   # Ensure the release PR does not contain an unexpected (e.g. 2.0.0) major version release
   # Add "MAJOR_VERSION_ALLOWED=component1,component2" to the PR description to allow major version
diff --git a/Gax/.gitignore b/Gax/.gitignore
index 94e81fe0df3..4f6a8850478 100644
--- a/Gax/.gitignore
+++ b/Gax/.gitignore
@@ -6,6 +6,7 @@ composer.lock
 composer-test.lock
 vendor/
 build/artifacts/
+tests/Conformance/showcase.pem
 artifacts/
 .idea
 .metadata