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

Trust 80%Fully autonomoussuccess · first tryCompare

Estimated cost: $0.20
Wall time: 41s
Human step-ins: 0
Outcome: Pass

Compare with other models on this task →

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).

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 199813127). 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 0.43 (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-opus-5.5: $0.200172. Score: 6/6. 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: $0.20
Wall time: 41s
Human step-ins: 0
Turns: 7

Model usage
Model	Input tok	Output tok	Cost
AClaude Opus 5.5anthropic/claude-opus-5.5effort default (no --effort flag) · thinking on	150,243	3,953	$0.20

Reproduce this run

Use the use case prompt on the use case page.
Same setup: Claude Opus 5.5 (anthropic/claude-opus-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.

Was this useful?

⇄ Rerun on another model

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

[
 {
  "duration_api_ms": 38536,
  "stop_reason": "end_turn",
  "session_id": "[REDACTED]",
  "total_cost_usd": 0.2001722,
  "usage": {
   "input_tokens": 14,
   "cache_creation_input_tokens": 11668,
   "cache_read_input_tokens": 138561,
   "output_tokens": 3953,
   "output_tokens_details": {
    "thinking_tokens": 608
   },
   "server_tool_use": {
    "web_search_requests": 0,
    "web_fetch_requests": 0
   },
   "service_tier": "standard",
   "cache_creation": {
    "ephemeral_1h_input_tokens": 11668,
    "ephemeral_5m_input_tokens": 0
   },
   "inference_geo": "global",
   "iterations": [
    {
     "input_tokens": 2,
     "output_tokens": 553,
     "cache_read_input_tokens": 23567,
     "cache_creation_input_tokens": 247,
     "cache_creation": {
      "ephemeral_5m_input_tokens": 0,
      "ephemeral_1h_input_tokens": 247
     },
     "type": "message"
    }
   ],
   "speed": "standard",
   "fallback_credit": null
  },
  "modelUsage": {
   "claude-opus-5-5": {
    "inputTokens": 14,
    "outputTokens": 3953,
    "cacheReadInputTokens": 138561,
    "cacheCreationInputTokens": 11668,
    "webSearchRequests": 0,
    "costUSD": 0.2001722,
    "contextWindow": 1000000,
    "maxOutputTokens": 128000,
    "thinkingTokens": 608,
    "canonicalModel": "claude-opus-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,
   "failed": 0,
   "killed": {
    "parent": 0,
    "user": 0,
    "system": 0
   },
   "refused": {
    "depth_limit": 0,
    "concurrency_limit": 0,
    "budget": 0
   },
   "by_type": {}
  },
  "safety_stops": 0,
  "is_error": false,
  "num_turns": 7,
  "subtype": "success",
  "api_error_status": null,
  "result": "I wrote `out/scene.html`: one self-contained file (2,645 bytes) with no URLs. It draws a 640\u00d7400 canvas showing the 600 px track and both carts, and animates them with `requestAnimationFrame` from the moment it loads.\n\n**How it works:** The motion is calculated exactly rather than stepped frame by frame. The page works out when the next event happens (an end-stop bounce or a cart-cart collision) and builds a list of motion segments from those times. Both the drawing and `window.sceneState()` read the position at the current `performance.now()`. So the state the function returns is what's on screen, positions are exact between events, and collisions use the elastic formulas with the 0.5 kg and 3.0 kg masses. The track sits at stage x 0..600, so the positions it reports are stage pixel coordinates.\n\n**Checks I ran:**\n- **Physics:** I ran the page's script under Node with a fake clock, sampling every 50 ms over 10 s. Momentum is unchanged through each cart-cart collision and the energy figure stays at 27,225 throughout. The carts never left the track and never overlapped. The first collision is at about 1.13 s, inside the 3 s test window.\n- **Browser:** In headless Chrome the page loads with the correct title and logged no console errors or exceptions. The only error lines came from Chrome failing to reach the system message bus (D-Bus), which has nothing to do with the page.\n\nI didn't run the real grading harness, so these checks were not run: the screenshot comparison, sampling `sceneState()` in a live browser, and watching for network requests.",
  "ttft_ms": 1840,
  "type": "result",
  "duration_ms": 40218,
  "uuid": "[REDACTED]",
  "ttft_stream_ms": 1051,
  "time_to_request_ms": 330,
  "first_content_frame_ms": 1052,
  "queued_turn_count": 0,
  "result_index": 0
 }
]