Claude Fable 5.1 in Claude Code 2.1.280
skills off
The model's own page, run in a sandboxed frame only when you ask (a page that needs its own origin opens in a new tab on a separate demo site). Phones get a full-screen player capped at 1.5x pixel density (2x on larger screens) so it stays smooth; the original page runs uncapped. It starts in its auto-tour (T switches to play mode on a keyboard).
Recorded from the live demo (stepped clock). Preview video recorded by this site from the live demo. The moving picture above is that preview; the button runs the real page.
Wall time 42m 34sCost $11.59 reported
Generation timelapse
Generation timelapse (the agent's screen during the run, sped up). This is not the finished video. Download video (888 KB).
Review
No verdict yet.
The full review
Stopped by us. Stopped by us (box row cap reached (2847s); stopped by the box lane so the run ships as partial); not a model failure.
Scores
Not scored: only runs that finished on their own are scored.
Downloads
Files actually published for this run. Original output, site-made previews and post-run conversions are labelled separately.
The exact prompt
as run, 725 characters. Every result for this prompt
Build a conceptual X-16 engine in 3D with Three.js: four cylinder banks, one crankshaft and exposed mechanics inspired by experimental multi-bank engine architectures. Make it animate (pistons, rods and crank moving in sync) with orbit controls. Everything is built in code from Three.js geometry, shaders and materials; no external models or textures. Build it as a single self-contained index.html in the current directory. Three.js may load from a CDN or be vendored. You may serve it locally and open it in headless chromium (/usr/bin/chromium, software WebGL, no GPU) to screenshot and inspect your own output, and iterate on your own before finishing. Close any browser you open as soon as you've taken your screenshot.
How it was made
Versions saved during the run
3 intermediate outputs, in the order the model wrote them.
Step by step
The prompt, every agent turn and tool call (tool name and a one-line summary; inputs and outputs are not shown), then the final message. The full transcript is 2.3 MB; it is published as a scrubbed, compressed download rather than shown on the page.
Show all 38 steps
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Download the full transcript Claude Code session JSONL, 118 KB, gzip. Scrubbed: anything that looks like a key, token, e-mail address or phone number is replaced, and account details and the test machine's file paths are removed.
Cost breakdown
Headline cost $11.59, as reported by Claude Code (its own bill for the run). The list-price estimate from the token counts is $11.58.
| Tokens by type | Tokens | $ per 1M | Cost |
|---|---|---|---|
| Input (uncached) | 646 | $10.00 | $0.0065 |
| Cache write | 313,052 | $12.50 | $3.9131 |
| Cache read | 2,400,345 | $0.25 | $0.6001 |
| Output | 141,157 | $50.00 | $7.0579 |
| of which reasoning | 106,106 | billed as output |
- Total computed from tokens
- $11.58
- Total reported by the harness
- $11.59
- Difference
- computed $11.58 vs reported $11.59 (diff -0.02)
Claude Code 2.1.280 reported its own total; token counts x list prices shown beside it.
Prices: Project price table (vendor list prices), 2026-09-22.
Run notes
- frozen prompt (written): engine/prompts_written/x16_engine.txt: a new test's prompt written by us from the project lead's brief (zero results)
- plain wave-1-equivalent cc_config copy (settings.json + .claude.json; no ECC files)
- Mode: interactive TUI in tmux (160x48), inside bubblewrap sandbox
- Context setting: 1M ([1m] model name)
- Isolation audit: outside paths seen