--- /dev/null
+# Investigation: IBM Plex Serif
+
+## Summary
+
+| Field | Value |
+|-------|-------|
+| Family Name | IBM Plex Serif |
+| Slug | ibm-plex-serif |
+| License Dir | ofl |
+| Repository URL | https://github.com/googlefonts/plex |
+| Commit Hash | 43279c151110b30d65a582261a5ddefd5c75c7be |
+| Config YAML | none (sources exist at commit, override needed) |
+| Status | missing_commit |
+| Confidence | HIGH |
+
+## Source Data (METADATA.pb)
+
+```
+source {
+ repository_url: "https://github.com/googlefonts/plex"
+ files {
+ source_file: "LICENSE.txt"
+ dest_file: "OFL.txt"
+ }
+ files {
+ source_file: "Google-Fonts-Fixes/descriptions/DESCRIPTION.en_us.html"
+ dest_file: "DESCRIPTION.en_us.html"
+ }
+ files {
+ source_file: "Google-Fonts-Fixes/fonts/IBM-Plex-Serif/fonts/complete/ttf/IBMPlexSerif-Bold.ttf"
+ dest_file: "IBMPlexSerif-Bold.ttf"
+ }
+ files {
+ source_file: "Google-Fonts-Fixes/fonts/IBM-Plex-Serif/fonts/complete/ttf/IBMPlexSerif-BoldItalic.ttf"
+ dest_file: "IBMPlexSerif-BoldItalic.ttf"
+ }
+ files {
+ source_file: "Google-Fonts-Fixes/fonts/IBM-Plex-Serif/fonts/complete/ttf/IBMPlexSerif-ExtraLight.ttf"
+ dest_file: "IBMPlexSerif-ExtraLight.ttf"
+ }
+ files {
+ source_file: "Google-Fonts-Fixes/fonts/IBM-Plex-Serif/fonts/complete/ttf/IBMPlexSerif-ExtraLightItalic.ttf"
+ dest_file: "IBMPlexSerif-ExtraLightItalic.ttf"
+ }
+ files {
+ source_file: "Google-Fonts-Fixes/fonts/IBM-Plex-Serif/fonts/complete/ttf/IBMPlexSerif-Italic.ttf"
+ dest_file: "IBMPlexSerif-Italic.ttf"
+ }
+ files {
+ source_file: "Google-Fonts-Fixes/fonts/IBM-Plex-Serif/fonts/complete/ttf/IBMPlexSerif-Light.ttf"
+ dest_file: "IBMPlexSerif-Light.ttf"
+ }
+ files {
+ source_file: "Google-Fonts-Fixes/fonts/IBM-Plex-Serif/fonts/complete/ttf/IBMPlexSerif-LightItalic.ttf"
+ dest_file: "IBMPlexSerif-LightItalic.ttf"
+ }
+ files {
+ source_file: "Google-Fonts-Fixes/fonts/IBM-Plex-Serif/fonts/complete/ttf/IBMPlexSerif-Medium.ttf"
+ dest_file: "IBMPlexSerif-Medium.ttf"
+ }
+ files {
+ source_file: "Google-Fonts-Fixes/fonts/IBM-Plex-Serif/fonts/complete/ttf/IBMPlexSerif-MediumItalic.ttf"
+ dest_file: "IBMPlexSerif-MediumItalic.ttf"
+ }
+ files {
+ source_file: "Google-Fonts-Fixes/fonts/IBM-Plex-Serif/fonts/complete/ttf/IBMPlexSerif-Regular.ttf"
+ dest_file: "IBMPlexSerif-Regular.ttf"
+ }
+ files {
+ source_file: "Google-Fonts-Fixes/fonts/IBM-Plex-Serif/fonts/complete/ttf/IBMPlexSerif-SemiBold.ttf"
+ dest_file: "IBMPlexSerif-SemiBold.ttf"
+ }
+ files {
+ source_file: "Google-Fonts-Fixes/fonts/IBM-Plex-Serif/fonts/complete/ttf/IBMPlexSerif-SemiBoldItalic.ttf"
+ dest_file: "IBMPlexSerif-SemiBoldItalic.ttf"
+ }
+ files {
+ source_file: "Google-Fonts-Fixes/fonts/IBM-Plex-Serif/fonts/complete/ttf/IBMPlexSerif-Thin.ttf"
+ dest_file: "IBMPlexSerif-Thin.ttf"
+ }
+ files {
+ source_file: "Google-Fonts-Fixes/fonts/IBM-Plex-Serif/fonts/complete/ttf/IBMPlexSerif-ThinItalic.ttf"
+ dest_file: "IBMPlexSerif-ThinItalic.ttf"
+ }
+ branch: "master"
+}
+```
+
+## Investigation
+
+### METADATA.pb Analysis
+
+The METADATA.pb has a `source` block with `repository_url: "https://github.com/googlefonts/plex"` and `branch: "master"`, but is **missing the `commit` field**. The file mappings pull static TTFs from `Google-Fonts-Fixes/fonts/IBM-Plex-Serif/fonts/complete/ttf/`. The fonts are 14 static TTFs: 7 weights (Thin through Bold) in both Roman and Italic.
+
+### Git History in google/fonts
+
+The TTF file history shows four commits:
+
+```
+b598f5e3a IBM Plex Serif: Version 2.6 added (#3544)
+115c6eb01 Add updated and new versions of IBM Plex (#1837)
+02d76fa55 ibmplexserif: v2.001 Bold added. (#1488)
+e39edaea9 ibmplexserif: v2.001 added (#1482)
+```
+
+The most recent commit `b598f5e3a` (by Yanone, 2021-06-23) is the authoritative onboarding commit for the current TTF files. Its commit body contains three squashed gftools-packager sub-commits:
+
+1. "[gftools-packager] IBM Plex Serif: Version 2.6 added"
+2. "IBM Plex Serif Version 2.6 taken from the upstream repo https://github.com/googlefonts/plex at commit https://github.com/googlefonts/plex/commit/43279c151110b30d65a582261a5ddefd5c75c7be."
+3. "[gftools-packager] ofl/ibmplexserif remove METADATA "source". google/fonts#2587"
+
+The third sub-commit removed the `source` block from METADATA.pb (per issue #2587 which cleaned up incomplete source blocks). The source block was later re-added, but without the commit hash.
+
+IBM Plex Serif was originally added to Google Fonts in 2018 (`e39edaea9`), updated in 2019 (`115c6eb01`), and last updated to Version 2.6 in June 2021 (`b598f5e3a`). The Version 2.6 commit represents the current state of the files in google/fonts.
+
+### Upstream Repository Verification
+
+The plex repo is cached at `upstream_repos/fontc_crater_cache/googlefonts/plex/`.
+
+Commit `43279c151110b30d65a582261a5ddefd5c75c7be` exists in the cache. At this commit, source design files exist for IBM Plex Serif:
+
+- `IBM-Plex-Serif/sources/masters/IBM Plex Serif Roman.designspace`
+- `IBM-Plex-Serif/sources/masters/IBM Plex Serif Italic.designspace`
+- `IBM-Plex-Serif/sources/masters/IBM Plex Serif-Bold.ufo/features.fea`
+- `IBM-Plex-Serif/sources/masters/IBM Plex Serif-Bold Italic.ufo/features.fea`
+- `IBM-Plex-Serif/sources/masters/IBM Plex Serif-Italic.ufo/features.fea`
+- `IBM-Plex-Serif/sources/masters/IBM Plex Serif-Regular.ufo/features.fea`
+- `IBM-Plex-Serif/sources/masters/IBM Plex Serif-Thin.ufo/features.fea`
+- `IBM-Plex-Serif/sources/masters/IBM Plex Serif-Thin Italic.ufo/features.fea`
+- Plus per-weight `.vfb` instance files for both postscript and truetype
+
+The `Google-Fonts-Fixes/packager/serif.yaml` file at this commit is a gftools-packager config (not a gftools-builder config.yaml). It maps pre-built TTFs from `Google-Fonts-Fixes/fonts/IBM-Plex-Serif/fonts/complete/ttf/` to their destinations.
+
+No gftools-builder `config.yaml` exists in the upstream repo or in the `ofl/ibmplexserif/` directory in google/fonts.
+
+### Source Files
+
+IBM Plex Serif has two `.designspace` files and 6 UFO masters (`IBM-Plex-Serif/sources/masters/`) at the referenced commit. The actual fonts in google/fonts are pre-compiled TTFs copied from `Google-Fonts-Fixes/`, not compiled directly from sources. An override `config.yaml` could be created pointing to the `.designspace` files.
+
+## Conclusion
+
+The METADATA.pb source block is missing the `commit` field. The correct commit hash is `43279c151110b30d65a582261a5ddefd5c75c7be`, sourced directly from the gftools-packager message in the google/fonts commit `b598f5e3a`. This commit is verified to exist in the upstream plex repo cache.
+
+Source files (`.designspace` + `.ufo` masters) exist at that commit. IBM Plex Serif has separate Roman and Italic designspace files:
+- `IBM-Plex-Serif/sources/masters/IBM Plex Serif Roman.designspace`
+- `IBM-Plex-Serif/sources/masters/IBM Plex Serif Italic.designspace`
+
+An override `config.yaml` should be created in the `ofl/ibmplexserif/` directory in google/fonts pointing to these sources.
+
+Action needed: Add `commit: "43279c151110b30d65a582261a5ddefd5c75c7be"` to the METADATA.pb source block, and create an override `config.yaml`.