Once per year The TeX Users Group releases TeX Live, a free and comprehensive distribution of the TeX document production system, enabling users to install a complete TeX setup for all common operating systems—including GNU/Linux, macOS, and Windows. Each release of TeX Live contains a point-in-time “snapshot” of the current/latest versions of all major TeX engines; LaTeX and LaTeX macro packages from The Comprehensive TEX Archive Network (CTAN), together with TeX-related programs and fonts that are free to use and distribute.
Between TeX Live releases the TeX community continues to innovate: new or updated TeX/LaTeX packages are uploaded to CTAN, new versions of TeX engines, and related software, are released—ready for inclusion in the next TeX Live distribution. This constant innovation is a big part of what makes TeX useful and relevant today, over 40 years after it was first created. However, that innovation also brings the potential for changes to LaTeX packages, or TeX-related software, which introduce incompatibilities that can prevent your existing documents from compiling, even though you haven't made any changes.
TeX Live is also used by Overleaf, enabling our compile servers to provide the real time preview of the typeset PDFs created by your projects. Because each release of TeX Live brings a suite of new or updated software, prior to upgrading our TeX Live installation Overleaf needs to make sure that our users’ documents will continue to compile successfully.
TeX Live is an important component of Overleaf and prior to upgrading we recompile a large test suite of documents, including roughly 5000 from our gallery of templates, examples and articles to check for breaking changes—including errors and any significant visual change(s) to the compiled output. We also measure the comparative time it takes to render documents. We identify significantly slower renders and try to make them faster. As a result of those tests we update templates that we have produced—this is why it sometimes takes us a while to update our TeX Live! However, the result is hopefully a more stable experience for our users.
Despite our testing, updates made to LaTeX, TeX engines, or important fonts and packages in TeX Live, can sometimes introduce incompatibilities, breaking changes and deprecations that are beyond our control. Given the scale of TeX Live and the wealth of packages and tools it provides, we can’t rule out breaking changes, but we will have tried our best to minimize any impact on our users.