--- /dev/null
+# Zen Maru Gothic — Upstream Source Investigation
+
+**Model**: Claude Opus 4.6
+**Date**: 2026-03-12
+
+## Summary
+
+The upstream repository for Zen Maru Gothic was identified as [https://github.com/googlefonts/zen-marugothic](https://github.com/googlefonts/zen-marugothic), 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-marugothic` was queried via the GitHub API to retrieve the latest commit on the `main` branch.
+
+The latest commit on `main` was identified as `553c872b216d1290e2902a466edcdc9682f0df6a`, 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-marugothic
+Commit: 553c872b216d1290e2902a466edcdc9682f0df6a
+Branch: main
+Status: commit hash added
+Confidence: high (verified via GitHub API)
+```