On the same 3D brief, a fishing sailboat in a night storm, Claude Sonnet 5.5 worked for 25 minutes for about $3.93 at API rates, against 39 minutes and $6.96 for Claude Opus 5.5. But the page Sonnet 5.5 delivered stays black because of a single faulty line. Once fixed, its storm is as good as Opus's, which remains the only one to work first time.
Anthropic released Claude Sonnet 5.5 on 28 September 2026, six days after Claude Opus 5.5, and sells it at half the price. The next day I gave it the brief Opus 5.5 had already received, a fishing boat tossed about by a night storm, in 3D, to see what you lose by paying half as much.
Both models worked in Claude Code, Anthropic’s coding assistant, which writes files on the computer, runs commands and checks its own work. The bench below runs both storms on your own machine, with nothing to install, and the full-screen view puts them side by side. Sonnet 5.5’s scene appears there fixed by one line, for a reason explained further down.
La consigne de nos deux premiers duels, un voilier de pêche dans une tempête de nuit en 3D, cette fois pour les deux modèles d'Anthropic sortis en septembre 2026. La scène d'Opus 5.5 s'exécute telle qu'elle a été livrée. Celle de Sonnet 5.5 est corrigée d'une ligne : livrée telle quelle, elle reste noire.
Shared prompt
Crée une scène 3D en three.js, dans un seul fichier index.html autonome, sans build ni dépendance locale (three.js chargé depuis un CDN par import map en module ES, version r170 ou plus récente).
Sujet : un voilier de pêche navigue de nuit sur une mer agitée, en pleine tempête.
- Mer : surface animée avec des vagues (déplacement de vertex), reflets sombres, écume discrète sur les crêtes si possible.
- Ciel : nuit noire, nuages bas, pluie visible (particules) poussée par le vent.
- Éclairs : toutes les quelques secondes, un éclair illumine brièvement toute la scène (flash, fort contraste, silhouette des nuages), avec un délai aléatoire entre deux éclairs.
- Bateau : coque, pont, mât, gréement et voile, modélisés uniquement avec des primitives three.js (aucun modèle externe, aucune texture externe). Il tangue et roule en suivant les vagues.
- Lanternes : au moins trois lanternes accrochées au bateau, lumière chaude et vacillante, qui éclairent le pont et l'eau autour du bateau.
- Caméra : contrôles orbitaux (OrbitControls) avec une position de départ qui met le bateau en valeur.
- Performance : viser 60 images par seconde sur un ordinateur portable ; le redimensionnement de la fenêtre est géré.
- Interface : aucune, à part un petit texte discret en bas à gauche indiquant les commandes.
Contraintes : tout le code (HTML, CSS, JavaScript) dans index.html ; pas de fichiers supplémentaires ; le fichier doit fonctionner en l'ouvrant directement dans un navigateur moderne (Chrome, Firefox, Safari). Ne pose pas de question, livre le fichier complet.
Protocol
La même consigne, en français, que lors des duels du 7 et du 22 septembre 2026, envoyée telle quelle, sans échange ensuite. Claude Opus 5.5 a travaillé le 22 septembre 2026, Claude Sonnet 5.5 le 29 septembre 2026, le lendemain de sa sortie, tous deux dans Claude Code, réglés sur le niveau de réflexion « xhigh », avec les mêmes réglages d'origine et la même sandbox : écrire dans un dossier vide et chercher sur le web, sans sortir de ce dossier ni ouvrir de navigateur. Aucun des deux n'a vu sa scène avant de la rendre. Le fichier livré par Sonnet 5.5 s'arrête sur une erreur dès la première image et n'affiche rien : la scène présentée ici est corrigée d'une seule ligne, le reste est identique au livrable. Mesures : temps de travail, coût au tarif public de l'API, respect point par point de la consigne, erreurs au chargement, rendu dans Chrome en 1 280 × 720, fluidité sans carte graphique puis sur une carte graphique récente, sans limite d'images par seconde, les deux scènes mesurées le même jour sur la même machine.
Runs in an isolated sandbox (iframe sandbox and CSP): no access to the site, cookies or your session. Nothing loads before you click.
Runs in an isolated sandbox (iframe sandbox and CSP): no access to the site, cookies or your session. Nothing loads before you click.
| Measurements | A · Claude Code · Claude Opus 5.5 | B · Claude Code · Claude Sonnet 5.5 |
|---|---|---|
| Temps de travail | 38 min 39 s | 25 min 26 s |
| Coût au tarif public de l'API | ≈ 6,96 $ | ≈ 3,93 $ |
| Fichier livré | fonctionne | page noire (1 ligne fautive) |
| Points de la consigne respectés | 13 sur 13 | 13 sur 13 une fois corrigé |
| Erreurs au chargement | 0 | 1 (0 une fois corrigé) |
| Poids de la page | 42 Ko | 54 Ko |
| Bateau | bateau de pêche à deux mâts, voiles tannées | lougre à un mât, grand-voile tannée et foc |
| Lanternes | 4, dont 3 qui se balancent | 4, qui se balancent toutes |
| Images par seconde sans carte graphique (rendu logiciel, sans limite) | 6 | 31, après baisse automatique de la résolution |
| Images par seconde sur carte graphique récente (Apple M5 Pro, sans limite) | 585 | 552 |
Verdict
Claude Opus 5.5 rend une tempête qui fonctionne du premier coup, en près de 39 minutes et pour environ 6,96 $ au tarif de l'API. Claude Sonnet 5.5 a travaillé 25 minutes pour environ 3,93 $, mais sa page livrée reste noire à cause d'une seule ligne fautive. Corrigée, sa scène vaut celle d'Opus : un lougre aux voiles tannées, une houle qui soulève le bateau, un éclair zébré qui se reflète sur la mer. Opus livre une scène qui marche, Sonnet une scène aussi belle qu'il faut savoir réparer.
Sonnet 5.5, the cheaper companion to Opus 5.5
On the 28 September launch page, Anthropic presents Sonnet 5.5 as the second model in the Claude 5.5 family, faster and cheaper than Opus 5.5. Opus is kept for complex work that calls for judgement, while Sonnet targets everyday, well-defined tasks. It is billed as more than 30% faster than Sonnet 5, and 9to5Mac noted on the same day that it keeps the same price.
The published figures put the two models very close together at programming. On Terminal-Bench 4.0, a test where the AI has to complete tasks in a terminal, Sonnet 5.5 scores 70.6% against 66.4% for Opus 5.5. On CursorBench 4.0, it stays two points behind, 55.5% against 57.8%. The page also shows demos built in a single HTML file, a flock of starlings or dunes shaped by the wind, exactly the kind of exercise our storm is.
On price, the API price list charges Sonnet 5.5 2 dollars per million tokens read and 10 dollars per million written, against 4 and 20 for Opus 5.5. A token is a piece of a word, the unit these models read and write in. So Sonnet 5.5 costs exactly half as much as Opus 5.5.
Same brief, same setting, one week apart
The request is the one from our face-off between Opus 5.5 and GPT-6 Sol, itself taken word for word from the first comparison of Claude Code and Codex. Everything has to fit in a single HTML file built on three.js, the free toolbox for 3D on the web. The brief lists thirteen points: waves with foam on the crests, a low, moonless storm sky, rain slanted by the wind, lightning at random intervals, a boat built from simple shapes that pitches with the waves, at least three flickering lanterns, a camera you steer with the mouse and a short help text.
I did not run Opus 5.5 again: its file and its working time are the ones from 22 September. Sonnet 5.5 worked on 29 September, with exactly the same settings: a single attempt, no touch-ups, and the “xhigh” reasoning level, one notch below the maximum, which Anthropic’s documentation also makes available to Sonnet 5.5. It sets how long the model gives itself to think, like the drafting time a pupil gets before handing in their paper. Each model worked inside the Claude Code sandbox, a sandpit that confines the AI to its working folder and to web searches (the details are in our guide to the Claude Code and Codex sandboxes). That sandbox also blocks the browser, so Opus 5.5 and Sonnet 5.5 alike programmed their storm blind.
The page Sonnet 5.5 delivered stays black
Opened as delivered, Sonnet 5.5’s file shows a black page with the controls legend in the bottom-left corner, and nothing else. After twelve seconds, a message says three.js could not be loaded from the internet. That message is wrong: three.js loads perfectly well. A reader who believed it would go looking for the fault in their own connection.
The real cause comes down to one line out of 1,278. On every frame, to lighten the mist during a lightning flash, the code asks a colour for an operation three.js only knows for positions in space, a bit like asking a paint pot for its latitude. The browser stops on that error from the very first frame, before it has drawn anything at all. You can see it for yourself with the original file:
Le fichier tel que Claude Sonnet 5.5 l'a rendu le 29 septembre 2026, sans aucune retouche. Il s'arrête sur une erreur dès la première image et la page reste noire.
Shared prompt
Crée une scène 3D en three.js, dans un seul fichier index.html autonome, sans build ni dépendance locale (three.js chargé depuis un CDN par import map en module ES, version r170 ou plus récente).
Sujet : un voilier de pêche navigue de nuit sur une mer agitée, en pleine tempête.
- Mer : surface animée avec des vagues (déplacement de vertex), reflets sombres, écume discrète sur les crêtes si possible.
- Ciel : nuit noire, nuages bas, pluie visible (particules) poussée par le vent.
- Éclairs : toutes les quelques secondes, un éclair illumine brièvement toute la scène (flash, fort contraste, silhouette des nuages), avec un délai aléatoire entre deux éclairs.
- Bateau : coque, pont, mât, gréement et voile, modélisés uniquement avec des primitives three.js (aucun modèle externe, aucune texture externe). Il tangue et roule en suivant les vagues.
- Lanternes : au moins trois lanternes accrochées au bateau, lumière chaude et vacillante, qui éclairent le pont et l'eau autour du bateau.
- Caméra : contrôles orbitaux (OrbitControls) avec une position de départ qui met le bateau en valeur.
- Performance : viser 60 images par seconde sur un ordinateur portable ; le redimensionnement de la fenêtre est géré.
- Interface : aucune, à part un petit texte discret en bas à gauche indiquant les commandes.
Contraintes : tout le code (HTML, CSS, JavaScript) dans index.html ; pas de fichiers supplémentaires ; le fichier doit fonctionner en l'ouvrant directement dans un navigateur moderne (Chrome, Firefox, Safari). Ne pose pas de question, livre le fichier complet.
Protocol
Voir le banc « Claude Opus 5.5 contre Claude Sonnet 5.5 ».
Runs in an isolated sandbox (iframe sandbox and CSP): no access to the site, cookies or your session. Nothing loads before you click.
Sonnet 5.5 had tested its code, though. With no browser, it built a stand-in for three.js, a fake library that pretends to answer, and ran 1,200 frames through it without an error. That stand-in said yes to every request, including the one that does not exist. It handed in its file with a warning that it had never seen it on screen, that its visual effects had never been tried, and a request to be told about any error in the console.
Fixed by one line, a storm as good as Opus’s
Once that line is rewritten, the scene starts without a single error and meets all thirteen points of the brief. That is the version running in the bench, and the rest of the file is identical to what Sonnet 5.5 delivered.
Sonnet 5.5 built a lugger, a single-masted fishing boat, with a large tanned mainsail the colour of rust and a small sail at the front, the rope ladder running up the mast, a cabin with lit windows, fishing buoys along the side and a pennant at the top of the mast. Four lanterns, at the bow, on the mast, on the cabin and at the stern, all swing like pendulums in time with the roll.
The sea is the higher of the two scenes. The swell lifts the boat, then hides it halfway behind a crest, with foam on the tops, around the hull and in the wake. A bolt of lightning strikes every two and a half to eight and a half seconds. Most draw a jagged arc across the sky, the others stay a diffuse glow in the clouds. With each flash, the sea turns silver all the way to the horizon. As with Opus 5.5, the rain is made of 16,000 stretched drops, orange in the lantern light, the same number chosen by both models without comparing notes.
The Opus 5.5 scene, described in our 22 September article, still packs in more detail: a two-masted fishing boat with brick-coloured sails, nets, crates, a ring buoy, and spray that bursts up when the bow dives. It is also darker between the flashes. Sonnet 5.5’s is easier to read and its storm is more spectacular.
Twenty-five minutes and 3.93 dollars
Sonnet 5.5 handed in its file after 25 minutes and 26 seconds. It thought for eleven minutes, checked what its sandbox allowed it to do, then wrote the whole page in one go at the twentieth minute. The last five minutes went on its tests and a few touch-ups. Opus 5.5 had taken 38 minutes and 39 seconds, including nearly half an hour of thinking before the first line.
Billed like a developer who calls the model directly from their own software, Sonnet 5.5’s work would come to about 3.93 dollars, against 6.96 for Opus 5.5. The list price is halved, and the bill for this storm drops by 44%. Sonnet 5.5 wrote a little less than Opus 5.5, but it reread its own work more often, and every reread costs money. Both runs were paid for with a Claude subscription, which deducts them from a usage allowance instead of billing them.
Just as smooth on a recent Mac
Both scenes were measured on the same day, on the same machine, under the same conditions, which is why the figures differ slightly from those published on 22 September. On a recent graphics chip, the one in a Mac with an M5 Pro, they are level: 585 frames per second for Opus 5.5 and 552 for Sonnet 5.5, measured with no cap. The brief asked for 60, and they show nearly ten times as many.
On a computer with no graphics card, where the processor draws everything on its own, the Opus 5.5 scene drops to 6 frames per second. Sonnet 5.5’s starts even lower, at around 3, then lowers its own image sharpness step by step and climbs back to 31 frames per second. Nobody had asked it for this automatic adjustment, which serves exactly the brief’s target of 60 frames per second.
Opus or Sonnet, which should you choose?
- For a result that works first time, Claude Opus 5.5. On this storm, it produced the only one of the two pages that displayed without anyone stepping in, at the cost of some forty minutes and nearly 7 dollars at API rates.
- To work fast and for less, while keeping an eye on the result, Claude Sonnet 5.5. Its scene is just as polished, quicker to produce and half the price per token, but a one-line error was enough to make it invisible. In Claude Code, a simple message such as “the page stays black, here is the console error” would have fixed it.
- For both, let the AI see what it is making. Opus 5.5 and Sonnet 5.5 worked blind, with no browser. With a screenshot or a console in front of it, this error shows up in the first second. Also bear in mind that an AI never hands in the same file twice: a second Sonnet 5.5 run might have avoided this error, or made a different one.
Key takeaways
- Claude Sonnet 5.5, released on 28 September 2026, costs half as much as Opus 5.5 at API rates.
- On the same 3D brief and at the same setting, it worked for 25 minutes for about 3.93 dollars, against 39 minutes and 6.96 dollars for Opus 5.5.
- The page it delivered stays black because of a single faulty line, which its own test missed. Once fixed, its storm is as good as Opus 5.5’s, with a higher swell and more visible lightning.
- Opus 5.5 delivers the only scene that works as is, and the richer one in detail.
- Both models programmed without a browser, so without seeing their storm, and each got just one attempt, on 22 September for Opus 5.5 and on the 29th for Sonnet 5.5.
