Re: Potential regression in natbib/beamer citation formatting in TeXLive 2026

As a workaround:

\begin{filecontents}{refs.bib}
@article{vaswani2017attention,
  title={Attention is all you need},
  author={Vaswani, Ashish and Shazeer, Noam and Parmar, Niki and Uszkoreit, Jakob and Jones, Llion and Gomez, Aidan N and Kaiser, {\L}ukasz and Polosukhin, Illia},
  journal={Advances in neural information processing systems},
  volume={30},
  year={2017}
}
\end{filecontents}

\documentclass{beamer}
\usepackage[authoryear,round]{natbib}

\makeatletter
\def\hyper@natlinkbreak#1#2{#1}
\makeatother

\begin{document}

\begin{frame}
Observed \citep{vaswani2017attention} (Missing comma)

Observed \citet{vaswani2017attention} (Missing parentheses around year)
\end{frame}

\begin{frame}[fragile]{References}
\bibliographystyle{plainnat}
\bibliography{refs.bib}
\end{frame}

\end{document}

> On 29. Mar 2026, at 01:57, Steven Paulson <[email protected]> wrote:
> 
> Dear TeXLive Team,
> I am writing to report a potential bug regarding citation formatting that appears when using the TeX Live 2026 distribution (verified on texlive.net/run).
> Description: When using natbib with the beamer document class, the citation punctuation (specifically the comma and parentheses placement) is not being rendered correctly.
>     • Observed output: (Vaswani et al.2017) and Vaswani et al.2017
>     • Expected output: (Vaswani et al., 2017) and Vaswani et al. (2017)
> It seems the round and authoryear options in natbib are being ignored or overridden in this environment. Downgrading back to TeXLive 2025 solves the issue.
> Minimal Working Example (MWE):
> \begin{filecontents}{refs.bib}
> @article{vaswani2017attention,
>   title={Attention is all you need},
>   author={Vaswani, Ashish and Shazeer, Noam and Parmar, Niki and Uszkoreit, Jakob and Jones, Llion and Gomez, Aidan N and Kaiser, {\L}ukasz and Polosukhin, Illia},
>   journal={Advances in neural information processing systems},
>   volume={30},
>   year={2017}
> }
> \end{filecontents}
> 
> \documentclass{beamer}
> \usepackage[authoryear,round]{natbib}
> 
> \begin{document}
> 
> \begin{frame}{Introduction}
> \begin{itemize}
>     \item Observed \citep{vaswani2017attention} (Missing comma)
>     \item Observed \citet{vaswani2017attention} (Missing parentheses around year)
> \end{itemize}
> \end{frame}
> 
> \begin{frame}[fragile]{References}
> \bibliographystyle{plainnat}
> \bibliography{refs.bib}
> \end{frame}
> 
> \end{document}
> 
> Environment Info:
>     • Distribution: TeX Live 2026 (released March 2026)
>     • Compiler: pdfLaTeX
>     • Platform: Verified via https://texlive.net/run, MacOS
> Best regards,
> Steven
>