--- /dev/null
+# Zen Old Mincho — Upstream Source Investigation
+
+**Model**: Claude Opus 4.6
+**Date**: 2026-03-12
+
+## Summary
+
+The upstream repository for Zen Old Mincho was identified as [https://github.com/googlefonts/zen-oldmincho](https://github.com/googlefonts/zen-oldmincho), which was already recorded in `METADATA.pb`. The source block was missing a `commit` field pointing to a specific upstream revision.
+
+## Investigation
+
+The repository at `googlefonts/zen-oldmincho` was queried via the GitHub API to retrieve the latest commit on the `main` branch.
+
+The latest commit on `main` was identified as `490d363e7886839ba1f86971cf874a1d70ad27f0`, authored on 2024-08-02, with message: "Update AUTHORS.txt".
+
+## Result
+
+The `commit` field was added to the `source` block in `METADATA.pb`:
+
+```
+Repo: https://github.com/googlefonts/zen-oldmincho
+Commit: 490d363e7886839ba1f86971cf874a1d70ad27f0
+Branch: main
+Status: commit hash added
+Confidence: high (verified via GitHub API)
+```