performance · same scenario on every build

How smoothly each one runs.

Extreme wave against a seawall, 1600×900, desktop Chrome with a GPU: six seconds idle, then fifty seconds of the wave. Two runs per build, averaged. The frame limiter is off, so FPS shows headroom, not what a 60 Hz screen displays.

FPS during the wavehigher is better

Fable 5.1 68 fps

Opus 5.5 25 fps

Sonnet 5 108 fps

Sonnet 5.5 56 fps

Frames over 50 msvisible stutters, lower is better

Fable 5.1 35

Opus 5.5 176

Sonnet 5 0

Sonnet 5.5 22

Worst framelongest freeze, lower is better

Fable 5.1 302 ms

Opus 5.5 218 ms

Sonnet 5 36 ms

Sonnet 5.5 155 ms

Load timeto the load event, lower is better

Fable 5.1 2.5 s

Opus 5.5 6.1 s

Sonnet 5 2.5 s

Sonnet 5.5 5.7 s

All numbers

	Fable 5.1	Opus 5.5	Sonnet 5	Sonnet 5.5
Solver runs on	main thread	Web Worker	main thread	main thread
Simulation grid	160 × 160 · 25,600 cells	240 × 200 · 48,000 cells	120 × 100 · 12,000 cells	160 × 140 · 22,400 cells
FPS idle	83 fps	105 fps	113 fps	127 fps
FPS during the wave	68 fps	25 fps	108 fps	56 fps
Frame time p50 / p99	13 / 50 ms	36 / 83 ms	9 / 18 ms	17 / 48 ms
Worst frame	302 ms	218 ms	36 ms	155 ms
Frames over 50 ms	35	176	0	22
Long-task time	2.3 s	10.0 s	0.0 s	1.2 s
Load time	2.5 s	6.1 s	2.5 s	5.7 s
JS heap	7 MB	27 MB	14 MB	14 MB

Reading it

Sonnet 5 is the fastest and smoothest, but it also has the smallest grid: 12k cells, half of Sonnet 5.5 and a quarter of Opus 5.5, so its water is the coarsest.
Fable 5.1 holds 65–70 FPS but stutters when the wave hits, with frames up to 300 ms.
Sonnet 5.5 sits in between, with occasional hitches and large run-to-run variance.
Opus 5.5 has the largest grid and the heaviest visuals. The solver runs in a Web Worker, yet rendering still drops to about 25 FPS during the wave. It is also the slowest to load.
All four stay usable after the Extreme wave; nothing crashed or blew up numerically.

On a laptop it's a different story

On a 2019 Intel MacBook Pro with a Retina screen, only Sonnet 5.5 ran without lag. It is the only build that lowers its own quality: when frames stay slower than about 34 ms, it drops the pixel ratio to 1. The other three render at 1.6–2× pixel ratio with 2048 px shadow maps and no fallback, which is 2.5–4 times the pixels for an integrated GPU. So the desktop ranking doesn't hold on weaker or high-DPI hardware.

Caveats: one desktop, two runs per build, measured with Playwright from requestAnimationFrame timings and the long-task observer.