GLM-5.1: Towards Long-Horizon Tasks

Simon Willison’s Weblog Subscribe Sponsored by: WorkOS — Production-ready APIs for auth and access control, so you can ship faster. GLM-5.1: Towards Long-Horizon Tasks. Chinese AI lab Z.ai's latest model is a giant 754B parameter 1.51TB (on Hugging Face) MIT-licensed monster - the same size as their previous GLM-5 release, and sharing the same paper. It's available via OpenRouter so I asked it to draw me a pelican: llm install llm-openrouter llm -m openrouter/z-ai/glm-5.1 'Generate an SVG of a pelican on a bicycle' And something new happened... unprompted, the model decided to give me an HTML page that included both the SVG and a separate set of CSS animations! The SVG was excellent, and might be my new favorite from an open weights model: But the animation broke it: That's the pelican, floating up in the top left corner. I usually don't do follow-up prompts for the pelican test, but in this case I made an exception: llm -c 'the animation is a bit broken, the pelican ends up positioned off the screen at the top right' GLM 5.1 replied: The issue is that CSS transform animations on SVG elements override the SVG transform attribute used for positioning, causing the pelican to lose its placement and fly off to the top-right. The fix is to separate positioning (SVG attribute) from animation (inner group) and use <animateTransform> for SVG rotations since it handles coordinate systems correctly. And spat out fresh HTML which fixed the problem! I particularly like the animation of the beak, which is described in the SVG comments like so: <!-- Pouch (lower beak) with wobble --> <g> <path d="M42,-58 Q43,-50 48,-42 Q55,-35 62,-38 Q70,-42 75,-60 L42,-58 Z" fill="url(#pouchGrad)" stroke="#b06008" stroke-width="1" opacity="0.9"/> <path d="M48,-50 Q55,-46 60,-52" fill="none" stroke="#c06a08" stroke-width="0.8" opacity="0.6"/> <animateTransform attributeName="transform" type="scale" values="1,1; 1.03,0.97; 1,1" dur="0.75s" repeatCount="indefinite" additive="sum"/> </g> Update: On Bluesky @charles.capps.me suggested a "NORTH VIRGINIA OPOSSUM ON AN E-SCOOTER" and... The HTML+SVG comments on that one include /* Earring sparkle */, <!-- Opossum fur gradient -->, <!-- Distant treeline silhouette - Virginia pines -->, <!-- Front paw on handlebar --> - here's the transcript and the HTML result. Posted 7th April 2026 at 9:25 pm Recent articles Anthropic's Project Glasswing - restricting Claude Mythos to security researchers - sounds necessary to me - 7th April 2026 The Axios supply chain attack used individually targeted social engineering - 3rd April 2026 Highlights from my conversation about agentic engineering on Lenny's Podcast - 2nd April 2026 This is a link post by Simon Willison, posted on 7th April 2026. css 235 svg 53 ai 1952 generative-ai 1733 llms 1700 pelican-riding-a-bicycle 103 llm-release 188 ai-in-china 92 glm 8 Monthly briefing Sponsor me for $10/month and get a curated email digest of the month's most important LLM developments. Pay me to send you less! Sponsor & subscribe Disclosures Colophon © 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026