Grok 4.5 landed this week with xAI calling it their smartest model yet, "trained alongside Cursor" for coding and agentic work. The internet's favorite way to vibe-check a new coding model is the build-off: hand it one prompt, see what app it spits out, post the clip. So we did it, but properly.

We gave Grok 4.5, GPT-5.5, Claude Opus 4.8, and Claude Fable 5 the exact same three prompts: build a single self-contained HTML file (no libraries, no network calls) for an interactive app. One shot each, no hand-holding, no prompt-fiddling. Then we loaded every result in a real browser, poked at it, and recorded what happened. Every clip below is the model's raw output, and you can click "play it live" to run the actual generated app yourself.

One rule on failures: if an app did not render at all, we allowed exactly one retry, and we tell you when we used it.

Round 1: a 3D Rubik's Cube that scrambles and solves

Build a colorful, 3D-looking Rubik's Cube with 'Scramble' and 'Solve' buttons. The cube must visibly animate its rotations.

This is the mean one. It needs real 3D math, per-face state, and animation, all in one file.

Play them live: Grok 4.5 · GPT-5.5 · Opus 4.8 · Fable 5

The Claudes ran away with this one. Opus 4.8 and Fable 5 both produced a proper, correctly colored 3D cube that scrambles and solves with animated turns, first try. Grok 4.5 stumbled here: its first attempt rendered the title and buttons but no cube at all (a blank void), so we spent our one allowed retry, and the second attempt produced a clean, colorful 3D cube. GPT-5.5 was the odd one out, rendering only a single dark face with barely any color instead of a full cube. Winner: Opus and Fable, tied.

Round 2: a particle gravity sandbox

An interactive particle gravity sandbox on a canvas: hundreds of particles with trails, clicking adds a heavy attractor. Make it mesmerizing.

Play them live: Grok 4.5 · GPT-5.5 · Opus 4.8 · Fable 5

Everyone shipped a working sandbox here, so this came down to taste. GPT-5.5 made the most genuinely mesmerizing one: glowing neon attractors with dense, swirling colored trails. Grok 4.5 went clean and orbital, with tidy attractor rings and colorful streaking particles. Fable 5 leaned into soft glowing orbs, and Opus 4.8 produced the busiest, most web-like particle field, great physics, slightly less eye-candy. Winner: GPT-5.5, on vibes.

Round 3: a playable Breakout game

A playable Breakout / brick-breaker on a canvas: paddle follows the mouse, ball breaks colorful bricks, with score and lives.

Play them live: Grok 4.5 · GPT-5.5 · Opus 4.8 · Fable 5

Dead heat. All four produced a polished, actually-playable brick-breaker with score, lives, and a glowing paddle, on the first try. Grok 4.5 and GPT-5.5 leaned hardest into the neon arcade look (GPT even racked up a score while our script batted the ball around). If we are splitting hairs, all four are ship-quality. Winner: everybody.

The receipts: speed and cost

Pretty demos are one thing; what does each model cost to run? We measured it ourselves with our own harness (three fixed prompts spanning coding, reasoning, and summarization, three reps each, capped at 400 output tokens) through the same provider path the app uses. Throughput is output tokens over total wall-clock latency, measured uniformly for every provider.

This is where Grok 4.5 flexes. It hit first token in under half a second, streamed at ~110 tokens/second (roughly double everything else here), and was the cheapest reply of the bunch, exactly the "intelligence per unit of time and cost" pitch xAI made. Its median wall-clock only looks mid-pack because it is verbose (it wrote the most tokens per answer), and its tail was spiky (a ~9s p95). GPT-5.5 was snappiest on short answers, Opus 4.8 sat in the balanced middle, and Fable 5 was the slowest and priciest, the tax you pay for the top of the intelligence charts.

Bonus round: draw something weird

Coding is one axis; spatial imagination is another. We asked each model for a single hand-authored SVG (no raster, no libraries) of a deliberately silly scene: a horse riding piggyback on an astronaut walking on the moon. Role reversal, two figures, one file.

Raw SVGs: Grok 4.5 · GPT-5.5 · Opus 4.8 · Fable 5

Fable 5 stole the show: a cowboy-hatted horse yelling "Giddy-up, human!" while a hunched astronaut wheezes "hff... hff...". That is not just drawing, that is comedy. GPT-5.5 was a close second with a gleeful horse shouting "WHEE!". Grok 4.5 nailed the brief cleanly with a colorful, readable scene. Opus 4.8 drew a characterful horse-on-astronaut too, but its raw SVG shipped with a duplicate attribute that trips strict SVG parsers (we rendered it leniently for the image above), a small but real correctness ding.

The verdict

• Grok 4.5 is the speed-and-value monster. It built a great Breakout and a slick gravity sim, streams about twice as fast as the field, and is the cheapest to run. Its only real miss was the hardest stateful task (a blank cube on the first try, fixed on the retry). If your workload is high-volume codegen where latency and cost compound, it is very hard to argue with. See Grok 4.5 vs GPT-5.5.
• Claude Opus 4.8 and Fable 5 are the most reliable builders. They were the only two to nail the 3D cube first try, and Fable had the funniest SVG. You pay for it in latency and price, especially Fable. See Grok 4.5 vs Opus 4.8.
• GPT-5.5 is the snappy stylist. Prettiest gravity sim, fastest short answers, but it flubbed the cube.

The honest headline: on a brand-new launch day, Grok 4.5 went toe to toe with the best models you can buy and won on speed and cost outright. Want to settle it with your own prompts? Every model here runs on one TryAI account, pay-as-you-go. Browse the models and start your own build-off.

Try it yourself

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