Claude Sonnet 5.5 (effort default (no --effort flag) · thinking on) on Animate two carts of different mass bouncing elastically on an air track in one self-contained HTML file

AClaude Sonnet 5.5default · thinking on · Claude Code 2.1.299 (headless -p) · cloud · 2026-10-23 · by @bobsiopener

Trust 80%Fully autonomouspartial · 0 retriesCompare

Estimated cost: $0.06
Wall time: 19s
Human step-ins: 0
Outcome: Partial

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Exact prompt

# Animate two carts of different mass bouncing elastically on an air track in one self-contained HTML file Make a small animated scene: a air track with two carts. Write one file, `out/scene.html`, that works opened straight from disk with no network access. `spec.json` gives the page title, the stage size and the scene parameters. **Looks are not scored**: the page is opened in a headless browser (800x600 window, UTC time zone, network blocked) and checked by objective tests only. ## Scene contract - Draw the scene on one `<canvas>` or `<svg>` stage of `width` x `height` CSS pixels (spec.json), visible on load, with `<title>` containing spec.json `title`. - Animate continuously from load (`requestAnimationFrame` or timers); no click is needed unless stated below. - Expose `window.sceneState()`, returning the scene's current state in stage pixel coordinates (origin top-left of the stage): `{carts: [{name, x, v}, ...]} (x = left edge of the cart along the track, 0..track_px - cart_width_px; v in px/s, positive = right)`. Extra fields are fine. It must describe what is actually drawn. - At time 0 (`performance.now()` 0) cart A and cart B are at their spec.json `x` with velocity `v`. There is no friction. Cart-cart collisions are perfectly elastic with the given masses, and both ends of the track bounce a cart back at the same speed. `sceneState()` must return the state at the moment it is called. - The page must log no errors and throw no exceptions. Keep the file at most 200,000 bytes; no external scripts, fonts, images or URLs (inline everything). ## Checks (partial credit = share passed) 1. `self_contained`: `out/scene.html` exists, is at most 200,000 bytes, references no http(s) or protocol-relative URL, and requests nothing from the network when opened. 2. `has_canvas_or_svg`: a visible `<canvas>` or `<svg>` of at least 300x200 CSS pixels is on the page. 3. `frames_change`: over 3 s, some later screenshot differs from the first in at least 0.1% of pixels, and at least 3 of 30 screenshots differ. 4. `motion_between_collisions`: `carts` names exactly A and B; between samples where neither velocity changes each cart moves v × Δt within 1.5 px; carts stay on the track and never overlap (by more than 0.5 px). 5. `elastic_collisions`: when only one cart's velocity changes between samples it reverses at an end stop (within 1%); when both change, the new velocities match a perfectly elastic collision of `mass_kg` A and B within 2% of |vA| + |vB|; at least one cart-cart collision is seen in 3 s. 6. `no_console_errors`: no uncaught exception, `console.error` or browser error is logged during the run. ## How this run works - Work on your own: nobody will answer questions in this task, and writing to `ask/` counts against the run. - Write only under `out/`. Create `out/` if it is missing. Inputs are synthetic; don't fetch anything from the network. - Scoring is partial credit: each listed check is pass/fail, and the score is the share passed. Numbers are compared to within 0.005 unless the task says otherwise.

Make a air track with two carts animation as one self-contained HTML file. A headless browser checks objective facts only: the file is offline and small, a canvas or SVG stage is drawn, frames change, the scene follows a timed specification (motion between collisions; elastic collisions) and nothing errors. A poster PNG and a short MP4 are captured for the gallery. Looks are not scored. Original benchmark task written for usecaserank.com (not based on a specific public post). Headless, offline run on a reproducible fixture. Each run's notes say how its cost was measured (estimates are marked). Rescore note (Oct 22, 2026): Rescore note: first scoring failed only ['elastic_collisions']; rescored once on the same output; first result kept as score_output.txt.orig-single-check-fail and media/b31ta08-claude-sonnet/, rescore in media/b31ta08-claude-sonnet-rescore/.

Success criteria: Passes the case's automated scorer (hidden tests / answer key, run after the agent finished).

Setup notes: Batch 31 case ta08-air-track-collisions (offline, synthetic inputs, seed 69687716). Autonomous case: no stand-in user and no step-ins expected; any file the solver wrote to ask/ is counted as a measured intervention (0) and blocks a pass. Prompt = TASK.md verbatim. Hidden key kept outside the solver's work dir. Scored with the case's scorer (python3 score.py WORKDIR KEYDIR, absolute paths); pass = every check true and no ask/ files. Tools: Read/Write/Edit/Glob/Grep/Bash, web disabled. Single run, no retries. 1-min load average at scoring 0.54 (8 cores). Creative case: looks are not scored; objective checks run in headless google-chrome (800x600, UTC, network blocked, Date mocked). Gallery media (3 s capture: poster.png + clip.mp4) written by the scorer to a fresh MEDIA_DIR per run (media/<run>/), SHA-256 in evidence.media; a single failed scene check is rescored once (both recorded in rescore). Time-zone results depend on the system time-zone database: tzdata 2026c-0+deb13u1 (Python zoneinfo). Claude Code's own reported cost for claude-sonnet-5.5: $0.057222. Score: 5/6. Cost is an ESTIMATE: measured tokens x pricing.json list price (Claude Pro subscription, nothing billed); input_tokens include cache reads and writes. Single run.

Estimated cost List-price estimate; not actually billed.

Output

Metrics

Estimated cost: $0.06
Wall time: 19s
Human step-ins: 0
Turns: 3

Model usage
Model	Input tok	Output tok	Cost
AClaude Sonnet 5.5anthropic/claude-sonnet-5.5effort default (no --effort flag) · thinking on	58,896	1,940	$0.06

Reproduce this run

Use the use case prompt on the use case page.
Same setup: Claude Sonnet 5.5 (anthropic/claude-sonnet-5.5, effort default (no --effort flag) · thinking on) via Claude Code 2.1.299 (headless -p), cloud.
It counts as a success only if it meets every success criterion: Passes the case's automated scorer (hidden tests / answer key, run after the agent finished).
Log model, tokens, wall time, human step-ins and the evidence log, then submit it as a reproduction. A different model? Submit a head-to-head rerun.

How runs are scored: Methodology.

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Automated checks

Trust 80% comes from these checks (how Trust % works).

Run date is not in the future : passed
Model is in the dated pricing table : passed
Cost recomputed from tokens matches : passed
Cached tokens are consistent : passed
Output throughput is plausible : passed
Autonomy matches step-ins : passed
Step-ins do not exceed turns : passed
Retries agree with first-try result : passed
Evidence log SHA-256 matches : passed
Evidence log is substantial : passed

Evidence log

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  "session_id": "[REDACTED]",
  "total_cost_usd": 0.057222499999999996,
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   "cache_creation_input_tokens": 8185,
   "cache_read_input_tokens": 50705,
   "output_tokens": 1940,
   "output_tokens_details": {
    "thinking_tokens": 457
   },
   "server_tool_use": {
    "web_search_requests": 0,
    "web_fetch_requests": 0
   },
   "service_tier": "standard",
   "cache_creation": {
    "ephemeral_1h_input_tokens": 8185,
    "ephemeral_5m_input_tokens": 0
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   "inference_geo": "global",
   "iterations": [
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     "output_tokens": 415,
     "cache_read_input_tokens": 19215,
     "cache_creation_input_tokens": 1509,
     "cache_creation": {
      "ephemeral_5m_input_tokens": 0,
      "ephemeral_1h_input_tokens": 1509
     },
     "type": "message"
    }
   ],
   "speed": "standard",
   "fallback_credit": null
  },
  "modelUsage": {
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    "outputTokens": 1940,
    "cacheReadInputTokens": 50705,
    "cacheCreationInputTokens": 8185,
    "webSearchRequests": 0,
    "costUSD": 0.057222499999999996,
    "contextWindow": 1000000,
    "maxOutputTokens": 128000,
    "thinkingTokens": 457,
    "canonicalModel": "claude-sonnet-5-5",
    "provider": "firstParty",
    "costBasis": "list"
   }
  },
  "permission_denials": [],
  "terminal_reason": "completed",
  "fast_mode_state": "off",
  "fast_mode_disabled_reason": "sdk_opt_in_required",
  "subagent_stats": {
   "spawned": 0,
   "requested": {
    "background": 0,
    "foreground": 0,
    "unset": 0
   },
   "started_in_background": 0,
   "max_depth": 0,
   "spawned_by_subagents": 0,
   "completed": 0,
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   "killed": {
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   "refused": {
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   "by_type": {}
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  "safety_stops": 0,
  "is_error": false,
  "num_turns": 3,
  "subtype": "success",
  "api_error_status": null,
  "result": "I wrote `out/scene.html`, but I haven't opened it in a browser or run any of the checks against it.\n\n- **Motion:** `window.sceneState()` works out the state from `performance.now()` each time it's called. It steps forward from the last state, jumping from one wall or cart-cart collision to the next. Between collisions each cart moves at constant velocity, so `x` advances by v \u00d7 \u0394t exactly.\n- **Collisions:** the A\u2013B collision uses the standard elastic formulas with A = 3 kg and B = 2 kg. A cart that reaches either end of the track reverses at the same speed.\n- **Drawing:** a canvas of 760\u00d7500 shows the track and two labelled carts, redrawn every frame from the same `sceneState()` values. The track is drawn from stage x = 0, so drawn positions match the reported ones.\n- **Start state:** A starts at x = 111 with v = 210, and B at x = 421 with v = \u2212120, as in `spec.json`.\n- **Self-contained:** the page is one file with everything inline and no external URLs, and it contains no `console.error` calls.",
  "ttft_ms": 1699,
  "type": "result",
  "duration_ms": 18311,
  "uuid": "[REDACTED]",
  "ttft_stream_ms": 1092,
  "time_to_request_ms": 274,
  "first_content_frame_ms": 1092,
  "queued_turn_count": 0,
  "result_index": 0
 }
]