Sonnet 5.5 and Sol 6.1, two sites get faster, and a closer look at tooltips

The AI releases kept coming, two big sites published how they got faster, and a lot of the CSS this week works around features that aren't everywhere yet. 56 posts from 31 sources.

Models, again

Anthropic released Sonnet 5.5, which Theo kind of likes but doesn't think you should use. OpenAI answered Opus 5.5 with Sol 6.1, "way way cheaper" in Theo's words, and midudev compares GPT-6 Sol and Luna with Opus and DeepSeek (in Spanish). He also covers Meta's Muse agent and its privacy problems and SAFA, a standards body for frontier models that Google, OpenAI and Anthropic are setting up. Syntax asks whether the Jev hype is overblown.

Not everyone is on board. Front-End Fire starts from DHH saying Basecamp no longer writes code by hand and asks whether frameworks still matter. David Bushell went the other way and won't use AI at all, and Rachel Andrew explains why AI is bad at writing tutorials: most of the work is understanding the subject and the reader, not producing words.

Performance

• GitHub spent three years moving github.com from styled-components to CSS Modules. It now ships more CSS, but server rendering takes 55% less time (Frontend Focus).
• Anthropic cut the time before Claude's apps can be typed in from 3.1s to 0.55s at p75. The culprits included em dashes pushing V8 onto a slower regex path, a stray location.reload() and a :root:has() selector costing 24ms per DOM change (JavaScript Weekly).
• Ben Schwarz uses airline websites as a case study for the state of web performance on ShopTalk.

CSS

• Piccalilli's The Index reached issue #200 with an all-CSS issue: new layout features, controlling when custom property values are computed, and scroll-triggered animations.
• Master.dev shows fallbacks for progress() until browser support grows, and Temani Afif fakes children-count() with scroll-driven animations.
• Adam Argyle uses anchor positioning to animate a textarea as field-sizing: content grows it.
• Last week's self-sizing iframes get a video from midudev on frame-sizing: content (in Spanish).
• Master.dev explains bidirectional text: why the exclamation mark ends up on the wrong side when English and Persian share a sentence.
• Installed PWAs on iOS 27 draw a blur over the top of the page. Modern Web Weekly tested what removes it, and theme-color isn't it.

HTML and accessibility

Patrick Brosset asked whether the title tooltip should be stylable, then looked at how it's actually used. On the top 5,000 domains it's mostly on links and images, and about 70% of those titles repeat the link text or alt text. The Front-End Checklist is back with a skill and an MCP server, so an agent can check your site against it.

Tools and JavaScript

• Vite+ 1.0 puts the Node runtime, package manager, dev server, linting, testing and builds behind one vp command. At TC39, three iterator proposals reached stage 4 (JavaScript Weekly).
• This Week In React has Panda CSS 2.0, with a compiler rewritten in Rust that removes the styling runtime from the bundle, and Vinext 1.0.
• TypeScript's DOM types lag behind the platform; Philip Walton's modern-web-types is a drop-in replacement that includes features once one engine ships them.
• David Bushell moved from Deno back to Node and shares his pnpm settings for delaying fresh, possibly malicious releases.
• Syntax's Scott and Wes are using GPUI for everything instead of Electron or Tauri.