Sonnet 5.5 vs Opus 5.5 vs GPT-6 Astra: I Tested All Three

If you just want the headline: Opus 5.5 won my real-world tests, but Sonnet 5.5 and GPT-6 Astra were close enough that the "best" model depends entirely on what you're building and what you're willing to pay. I ran all three through four hands-on builds — not benchmarks, actual projects — and the gaps were smaller than the spec sheets suggest. Here's exactly how each one performed, and how to pick the right one for your work.

So much for the AI slowdown. The last few weeks dropped three serious models back to back: GPT-6 Astra, Claude Opus 5.5, and Claude Sonnet 5.5. The obvious question is which one you should actually be using day to day — and the answer isn't as clean as "pick the biggest, most expensive one."

What Do the Benchmarks and Pricing Actually Say?

Before the hands-on tests, the numbers set up an interesting fight. Looking at the benchmarks where we have data for all three models, Opus 5.5 wins four out of five. That's the expected result — it's the heavyweight.

The surprise is Sonnet 5.5, the smallest of the three, beating every other model on Terminal-Bench 4. A cheaper, lighter model outscoring its bigger sibling on an agentic coding benchmark is exactly the kind of thing that should make you stop assuming flagship = best.

Pricing is where it gets practical:

• Sonnet 5.5 — $2 per million input tokens, $10 per million output. Roughly half the cost of Opus.
• Opus 5.5 — Anthropic's heavyweight, about double Sonnet's price.
• GPT-6 Astra — OpenAI's flagship and the priciest of the bunch, around 5x the cost of Sonnet.

Keep those price points in your head for every result below. A model that "wins" by a hair but costs five times as much isn't really winning.

Test 1: Can They Build a JavaScript Explainer Video in Pure Code?

The first test had nothing to do with video generators. I asked each model to write, in JavaScript, a 15-second explainer animation showing how subagents in Claude work — a hand-drawn visual style, audio included, all of it pure code. No AI video tools, no image generation. Just code that renders a video.

Sonnet 5.5 held up well. The audio and visuals matched up, and every beat of the animation had something happening on screen. The one knock: it moved so fast in places that it was genuinely hard to follow what was happening.

Opus 5.5 produced something very similar but a touch more polished. On the first pass it got the edge over Sonnet — same hand-drawn energy, slightly better execution.

GPT-6 Astra was the weak link here. Not nearly as dynamic, noticeably slower-paced, and honestly a little boring next to the two Anthropic outputs. The audio was weaker too.

Here's the catch that complicates the scoreboard: Sonnet and Opus each burned about 300,000 tokens on this, while Astra finished in roughly 70,000. Astra lost on quality but did it for a quarter of the token spend. Winner: Opus 5.5, closely followed by Sonnet.

Test 2: Which Model Designs the Best Landing Page?

Next up, front-end design: build a landing page for a fictional boutique hotel called Dune House. The Anthropic models start at a disadvantage here because they can't generate their own images the way Astra can. To level the field, I gave Sonnet and Opus access to the Higgsfield API so they could pull images and video on demand — pay-as-you-go instead of a fixed monthly subscription, which makes it a clean fit inside a Claude Code workflow when you only need assets here and there.

Sonnet 5.5 leaned into the big hero image look Anthropic models seem to love right now. It read like a real hotel site — a working "check availability" flow, imagery front and center, and a nice callback to the hero image down near the footer. The font choice and a clunky availability pill hurt it, but for a prompt with very little direction, it was solid.

Opus 5.5 did its own thing and did it better. It took creative liberties with the Dune House branding, added a logo that reacts to your mouse, used glassmorphism on the availability widget, leaned into an orange-to-black palette, animated numbers that tick up on scroll, and let you click through specific dates and room availability. More unique design decisions, less generic — this was the standout.

GPT-6 Astra was the cleanest of the three in the hero section — arguably my favorite single section across all three. If this is what "AI slop" looks like now, we're in a good spot. It beat Sonnet for me but didn't blow past Opus; it's genuinely subjective at the top.

The real takeaway: AI web design is in a great place when the gap between a $2 model and a 5x-pricier flagship is this small. Tokens: Sonnet and Opus around 200,000, Astra about 125,000. Winner: Opus 5.5, with Sonnet and Astra not far behind.

Test 3: Which Model Builds the Best 3D Sci-Fi Dashboard?

For the third test I let the models go wild: build a 3D travel dashboard web app that looks like something out of a sci-fi film. Loose direction on purpose. Anthropic models again got Higgsfield API access for any images or video they wanted.

Sonnet 5.5 went completely off the rails — in a fun way. An interactive globe you can zoom deep into, click a city like Paris or Tokyo and get generated imagery, pricing, temperature, and non-stop routes, with background music playing. Visually wild.

Opus 5.5 was slightly more restrained but added smarter touches: pick a departure city, see fares and flight times, and hit a key to "redraw the world" around your origin — flattening the globe into a flat map view. That globe-flattening trick pushed it ahead of Sonnet on visuals for me.

GPT-6 Astra went the opposite direction: subdued and practical. Departure city, dates, traveler count, cabin class, an explore button that surfaces destination info. Less spectacle, far more like something you'd actually ship and use.

This is the test where the "winner" flips depending on what you asked for. On pure visual spectacle, Opus 5.5 is first, then Astra, with Sonnet last because it went too far over the top. On functionality — an app you'd actually use — Astra wins clearly. And that's not Sonnet or Opus failing; given a prompt that invited chaos, they preferred form over function. Tokens: Opus and Sonnet around 300,000, Astra about half that.

Test 4: Which Model Makes the Best Browser Game?

Last test: game design. I had each model build a browser-based World of Tanks clone in Three.js, running entirely in the browser, no asset packs — everything generated from scratch.

Sonnet 5.5 nailed the basics: a loading screen, selectable tanks with distinct stats, switchable ammo types mapped to hotkeys, zoom, reload timers, and repair mechanics. It worked surprisingly well for a from-scratch build.

Opus 5.5 delivered a near-identical experience — same stat panels, same three ammo rounds, same minimap and zoom. A minor UI overlap in the bottom-right corner was the only real difference.

GPT-6 Astra shipped a slightly more simplistic UI with fewer on-screen stats, but a couple of genuinely nice touches: a map I liked better, more sensitive camera controls, and hit detection that reports the angle of impact — telling you whether a shot ricocheted based on whether it landed on the front or the side.

Honestly, this one's a tie on output. The products were functionally the same. The separator is cost: Sonnet took the most — about 750,000 tokens — Opus landed around 500,000, and Astra came in near 300,000. If you're paying by the token, Astra quietly wins the game test on efficiency alone.

So Which AI Model Should You Actually Use?

Add up all four tests and Opus 5.5 is the overall winner — but the margin is thin, and Astra and Sonnet are right behind it. That's genuinely big news if you work in the Anthropic ecosystem, because Sonnet 5.5 is a massive upgrade over Sonnet 5 at half the price of Opus. Sonnet 5 was basically unusable; Sonnet 5.5 is a model you can live in all day.

Here's how I'd actually choose:

• Default to Sonnet 5.5 for the vast majority of coding work. It's half the price of Opus, it won Terminal-Bench 4, and in these tests it traded blows with models costing far more.
• Reach for Opus 5.5 when you want the most polished, most creative output and the token cost is worth it — complex front-end design and visually ambitious builds.
• Use GPT-6 Astra when you want practical, functional results and better token efficiency, or when you need native image generation baked in. It's a model I use literally every day.

None of this is a knock on OpenAI. This competition is the reason the outputs are this good — Astra pushing hard is exactly what forces Anthropic to ship models this strong. The honest answer is to try all three on your own work and see what fits.

Frequently Asked Questions

Is Sonnet 5.5 better than Opus 5.5?

Not overall — Opus 5.5 won four of five benchmarks and took the edge in my real-world tests. But Sonnet 5.5 beat every model on Terminal-Bench 4, costs half as much, and performed close enough across the board that it's the smarter default for most coding work. Opus is worth it when you specifically want maximum polish.

How much does Sonnet 5.5 cost compared to Opus 5.5 and GPT-6 Astra?

Sonnet 5.5 runs $2 per million input tokens and $10 per million output — roughly half the price of Opus 5.5. GPT-6 Astra is the most expensive of the three at about 5x the cost of Sonnet, since it's OpenAI's flagship model.

Which model is best for front-end and web design?

In my hotel landing page and 3D dashboard tests, Opus 5.5 produced the most creative, polished designs. But GPT-6 Astra had the cleanest hero sections and the most practical, usable layouts, and it can generate its own images natively. For design specifically, it's close enough to come down to taste.

Can Claude models generate their own images like GPT-6 Astra?

Not on their own. In these tests I gave Sonnet 5.5 and Opus 5.5 access to the Higgsfield API so they could pull images and video pay-as-you-go. That levels the field with Astra's native image generation and slots cleanly into a Claude Code workflow.

Is GPT-6 Astra worth the higher price?

It depends on the job. Astra often used far fewer tokens than the Anthropic models and produced the most functional, practical results, plus native image generation. But for pure quality it didn't blow past Opus, so the 5x price premium is only worth it if efficiency or those specific features matter to your workflow.

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