Halden One, built by Opus 5.5 from a single brief. Scroll, and the cabinet opens: bracing, woofer, tweeter.
Choosing the model that builds your projects is the most important decision we make on your behalf. Most days you never see it: you describe what you want, leave the picker on Auto, and something has to decide who writes the code.
On October 13 we changed that decision. On Pro and above, Auto now runs on Claude Opus 5.5, Anthropic’s newest Opus. That same evening we gave it a brief we wrote to be hard, and watched what it made.
The test: a speaker that opens as you scroll
The brief was a one-page site for an imaginary Scandinavian speaker: oiled walnut, a brushed-aluminium front, a grey wool grille. The camera had to circle it as you scroll, lift the grille, open the cabinet to show what’s inside, and put it all back together for the price.
Opus 5.5 planned the site, wrote 28 files and had a working preview in 16 minutes. Then it did the part that is easy to promise and hard to build: the cabinet really opens. Claude Sonnet 5.5, which runs Auto on Builder, got the same brief and built a handsome speaker too. The inside just never came into view.
One brief is not a benchmark, and we keep measuring. But that gap, between a model that stops at the surface and one that finishes the idea, is what we want Pro to give you.
- 1M tokens of context: a whole project in view at once
- 16 min from the brief to a working Halden preview
- 28 files, planned and written in one run
What it does differently
- It keeps the whole project in mind. A context window of a million tokens. Your files, your brief and the conversation fit at once, so a change on page nine still remembers page one.
- It reads what you show it. Paste a screenshot, a sketch or a PDF. It reads images and files as well as words.
- You decide how hard it thinks. The Effort control beside the model runs from Quick to Maximum. It starts at Thorough.
- Straight from Anthropic. We call Anthropic’s own API, with a second route ready if the first is down.
- One mind per project. The same model reads your request and writes the code, so nothing gets lost between the two.
Claude Opus 5.5 at a glance
Anthropic’s newest Opus, now behind Auto on Pro.
- Made by: Anthropic
- Context window: 1M tokens
- Reads: text, images and files
- On Auto: Pro and above
- Available since: October 13, 2026
What changes for you
- On Pro and above. Leave the picker on Auto and Opus 5.5 builds. Nothing to switch on.
- On Builder. Auto runs Claude Sonnet 5.5, and Opus 5.5 is one click away in the picker.
- For 3D. 3D projects on Auto run on Claude Fable 5.1. Opus 5.5 is in the picker if you want to try it there.
- Your pick still wins. Choose any model yourself and Auto steps aside.
Try it: three prompts to start with
A booking site for a surf school in Ericeira, with lesson packages, a calendar and a page for each instructor.
A stock app for a small shoe shop: sizes, colours, low-stock alerts and a weekly order list.
A product page for a desk lamp that switches on as you scroll.
João Castro, founder of VULK
P.S. Send the first thing you build with Opus 5.5 to support@vulk.dev. It comes straight to us, and I’d love to show the best ones.
