# Source Serif: the default branch holds the binaries, the manifest says 4.5.1 and the newest tag says 4.005 > An open-source serif typeface designed to sit alongside a sans family, licensed under a licence that lets anyone use it, with five binary formats and a variable build committed to the repository. The page is a design history rather than a guide, and the interesting details are in the two places where the repository disagrees with itself. **adobe-fonts/source-serif** — Typeface for setting text in many sizes, weights, and languages. Designed to complement Source Sans. - Repository: https://github.com/adobe-fonts/source-serif - Website: https://adobe-fonts.github.io/source-serif - Stars: 2,388 · Forks: 165 - Language: CSS - License: OFL-1.1 - Published: 2026-09-28 · Updated: 2026-09-28 · Language: en - Canonical page: https://hysenlabs.com/projects/adobe-fonts-source-serif ## The default branch holds the binaries, the other one holds the sources This repository is split across two branches, and the one you land on by default is not the one with the sources in it. The branch the repository opens on is named for releases, and the package manifest agrees: its repository link points at that branch explicitly, including the branch name in the address. What sits on it is the built output. The top level is five directories of font files, one per binary format, plus a directory for the variable build, a demo folder, the licence file, the readme, and a set of stylesheets. The source files and the build instructions are on the other branch, named for the trunk, and the readme says so in one sentence and points there. So a type designer cloning this to work on the outlines takes the second branch, while anyone downloading the fonts takes the first by accident. The readme is explicit enough that you will not be confused if you read it, but an automated script that clones and looks for sources will find five directories of binaries and no build system. The readme is also unusually short for a typeface project. There is no specimen, no character map, no usage guidance, and no metric table. What it does have is a link to the technical readme in the wiki, which is where the design and engineering detail lives. ## The manifest says one version and the tags say another Two version numbers describe this project and they do not share a format. ```json "version": "4.5.1", ``` That is the manifest. The newest release tag is 4.005 with a suffix, titled as fonts version 4.005, and before it come 4.004 and 3.001, all with the same suffix and the same three-number shape. So the tags run 3.001, 4.004, 4.005, while the manifest is at 4.5.1. Read as decimals the manifest is newer, which is probably the intent. Read as the tag scheme the two are different numbering systems, and nothing on the page maps one to the other. That matters in practice for two ordinary tasks. A build script that derives its version from the manifest will print a number nobody can match to a release. And a support question that starts with the version number has to be resolved by asking which of the two schemes the reporter means. The licence is the one thing both files agree on cleanly: the manifest carries the SIL Open Font License identifier and the licence file sits at the root of the default branch, named with an extension rather than being the bare name most projects use. ## Six stylesheets, one per optical size Six stylesheet files sit at the root of the repository, and their names are the interesting part. ```text source-serif-caption.css source-serif-display.css source-serif-smtext.css source-serif-subhead.css source-serif-text.css source-serif-variable.css ``` Five of them are named for positions on an optical size scale rather than for weights: caption, subhead, text, small text, and display. That is not a naming convention the project invented. The design history in the readme records that version 4 arrived with optical sizes, which is the technique where a typeface is drawn differently at different text sizes rather than scaled uniformly, and each optical size therefore needs its own cut of the outlines and its own way to be selected. For a user this means the choice is not bold versus regular, it is which of five sizes you are setting. Small text is for running copy, text for body, subhead for headings, display for large settings, and caption for the smallest. The sixth file is the variable one, which is the same design delivered as a single file with a range of axes instead of a set of cuts. So a site using this typeface needs to decide which of the five it wants and wire the corresponding stylesheet, and the repository hands you six equally named files with no indication in the names of which is which beyond the axis they represent. ## The newest release on record is from January 2023 The repository has been touched recently and the font has not been released in years, and those two facts sit side by side without comment. The last push on the default branch is dated 2026-09-13. The newest release tag is from 2023-01-20, the one before it from 2021-01-25, and the one before that from 2019-10-11. So the release cadence is roughly every one to two years, with a long tail since the last one, while commits continue. The design history explains why that is plausible rather than alarming. The typeface is mature: it launched in 2014 with three weights, added three more the same year, extended its language coverage with Greek and Cyrillic in 2017, gained italics across the family in 2018, and gained optical sizes in 2021. A type family that reaches its optical size stage has finished the work that produces new releases, and the remaining commits are the steady kind: corrections, hinting, build fixes, and the metadata that keeps a repository tidy. The practical consequence for an adopter is that Source Serif is a finished design rather than one in progress. You are not waiting for the fourth optical size. What you may be waiting for is a platform to add the fonts to its catalogue, since five binary formats and a variable build have to be enumerated by whatever you deploy onto. ## The family was renamed at version 4 One entry in the design history is about naming rather than drawing, and it explains why almost every reference to this typeface online carries an old word. The 2021 entry for version 4 lists two changes: optical sizes, and a change of family name. The typeface launched as Source Serif Pro, and the professional suffix came off at version 4. Nothing about the design changed in that rename, which is why older tutorials, older stylesheets, and older conversations still say Pro while the current family does not. That is worth knowing before you spend an afternoon on a problem you do not have. If a font stack you copied from a five-year-old tutorial fails to load, the name in it may be the previous name of this family rather than a font that never existed. The same applies to the version numbers: a request for version 3 is a request for the pre-optical-size design, which is a different set of cuts from the current one even where the weight names look identical. The other entries follow the same pattern of recording a specific, dated change: three weights at launch, three more later in 2014, two alphabets and broader language support in 2017, italics across every style in 2018. It is a short, factual list, and it is the most useful thing on the page for anyone deciding whether this family covers what they need. ## Five formats are committed as binaries in the repository There is no package to install and no build step to run if you want the fonts. Each release is committed to the repository, and the release title names what goes out. Each release title names the five formats it ships: the OpenType and TrueType outlines for desktop use, the two web formats, and the variable build. the OpenType and TrueType outlines for desktop use, the two web formats, and the variable build. In the repository they live in one directory each, with the variable build in its own. That is a deliberate trade-off. A version control system is a poor place for large binaries, but committing them means a download is a clone away, a tag is immutable, and a fork can be patched without anyone rebuilding a toolchain. It also means the repository is large, and that a diff of a release is a diff of binary files. The manifest's keyword list is a compact summary of the same decision, and it includes a format that appears nowhere in the release title: a CFF2 keyword alongside OpenType, TrueType, the two web formats, and variable. That is the compact font format used by some variable pipelines, so either the repository ships more than the release title advertises or the keyword is aspirational. Nothing on the page settles it. One last detail worth noting: the primary language the repository reports is a stylesheet language. For a typeface project, that is a consequence of storing the shipped output rather than the sources, and it is the same branch split described at the top of this article showing up in a metadata field. ## Conclusion Use it when you need a serif that sits next to a sans family, covers a lot of scripts including Greek and Cyrillic, and costs nothing to ship. Three things to know before you adopt it. The family was renamed at version 4, so if you are following an older tutorial you are probably looking for a different name than the one in your font stack. The newest release on record is from January 2023 even though the repository has been touched more recently, so treat the version you get as a snapshot rather than a moving target. And the source files live on a different branch from the built ones, which is unusual enough to trip up an automated pipeline. ## FAQ ### Is Source Serif a variable font? Yes, among the shipped formats. Each release title lists OpenType, TrueType, WOFF, WOFF2, and a variable font, the repository has a directory for the variable build alongside the static formats, and the package manifest's keyword list includes variable. ### is source serif pro free The typeface is licensed under the SIL Open Font License 1.1, and the licence file sits at the root of the repository. The package manifest carries the same licence identifier. ### What changed in Source Serif 4? Two things according to the design history: optical sizes, and a change of family name. The optical sizes are the reason the repository ships five named stylesheets, and the rename is why older material refers to the family with a professional suffix. ### Where are the Source Serif source files? On the repository's main branch, which holds the source files and build instructions. The default branch is the release branch, which carries the built fonts in five formats, the licence, and the readme. ### How do I choose between the Source Serif sizes? Each stylesheet corresponds to one position on the optical size scale rather than to a weight: caption, small text, text, subhead, and display, plus a separate variable stylesheet. You pick the one that matches what you are setting. ## Sources - [adobe-fonts/source-serif on GitHub](https://github.com/adobe-fonts/source-serif) - [License: OFL-1.1](https://github.com/adobe-fonts/source-serif/blob/release/LICENSE) - [Project website](https://adobe-fonts.github.io/source-serif) - [README](https://github.com/adobe-fonts/source-serif/blob/release/README.md) - [Releases](https://github.com/adobe-fonts/source-serif/releases) --- Hysen Labs editorial analysis, written from the project's own repository and release notes. Cite the canonical page: https://hysenlabs.com/projects/adobe-fonts-source-serif