diff --git a/.github/workflows/tree-sitter-upgrade-readiness.yml b/.github/workflows/tree-sitter-upgrade-readiness.yml
index 3d17e100d..74ce72a27 100644
--- a/.github/workflows/tree-sitter-upgrade-readiness.yml
+++ b/.github/workflows/tree-sitter-upgrade-readiness.yml
@@ -79,7 +79,8 @@ jobs:
         with:
           script: |
             const title = 'Tree-sitter 0.25 upgrade readiness';
-            const body = process.env.REPORT + '\n\n' +
+            const report = process.env.REPORT;
+            const body = report + '\n\n' +
               '<sub>Generated daily by `.github/workflows/tree-sitter-upgrade-readiness.yml`. ' +
               'Closes automatically when all blockers are resolved.</sub>';
             const { data: open } = await github.rest.issues.listForRepo({
@@ -91,6 +92,48 @@ jobs:
             });
             const existing = open.find(i => i.title === title);
             if (existing) {
+              // Extract ready/total count for the changelog comment.
+              const readyMatch = report.match(/\*\*(\d+)\/(\d+)\*\* grammars ready/);
+              const blockerMatch = report.match(/\*\*(\d+) blocker/);
+              const ready = readyMatch ? readyMatch[1] : '?';
+              const total = readyMatch ? readyMatch[2] : '?';
+              const blockers = blockerMatch ? blockerMatch[1] : '?';
+
+              // Find grammars whose status changed by diffing the old and
+              // new table rows.  Each row looks like:
+              //   | `tree-sitter-foo` | ... | Ready |
+              //   | `tree-sitter-foo` | ... | Blocking |
+              const parseRows = (md) => {
+                const map = {};
+                for (const m of md.matchAll(/\| `(tree-sitter-[^`]+)` \|.*?\| (\S+(?:\s\S+)*?) \|$/gm)) {
+                  map[m[1]] = m[2].trim();
+                }
+                return map;
+              };
+              const oldRows = parseRows(existing.body || '');
+              const newRows = parseRows(report);
+              const changes = [];
+              for (const [name, newStatus] of Object.entries(newRows)) {
+                const oldStatus = oldRows[name];
+                if (oldStatus && oldStatus !== newStatus) {
+                  changes.push(`\`${name}\`: ${oldStatus} → ${newStatus}`);
+                }
+              }
+
+              const today = new Date().toISOString().slice(0, 10);
+              let comment = `**${today}:** ${ready}/${total} ready. ${blockers} blocker(s) remaining.`;
+              if (changes.length > 0) {
+                comment += '\n\nChanges:\n' + changes.map(c => `- ${c}`).join('\n');
+              } else {
+                comment += ' No changes from previous run.';
+              }
+              await github.rest.issues.createComment({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                issue_number: existing.number,
+                body: comment,
+              });
+
               await github.rest.issues.update({
                 owner: context.repo.owner,
                 repo: context.repo.repo,