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Claude Opus 5.5 (effort default (no --effort flag) · thinking on) on Split a shared house's utility bills by days of occupancy, to the cent

AClaude Opus 5.5default · thinking on · Claude Code 2.1.299 (headless -p) · cloud · 2026-10-20 · by @bobsiopener

Trust 80%Fully autonomoussuccess · first try
Estimated cost
$0.11
Wall time
19s
Human step-ins
0
Outcome
Pass

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Summary

Exact prompt

# Split a shared house's utility bills by days of occupancy Inputs: `housemates.json` (each person's move-in and move-out dates; null means still living there), `bills.json` (each bill's amount, service period and who paid it). Rules: - A person occupies the house on every date from move_in to move_out, both inclusive. - For each bill, a person's days = the dates inside the bill's service period (both ends inclusive) that they occupy the house. - Share = bill amount x person's days / sum of all people's days for that bill, rounded half-up to the cent. - If the rounded shares don't add up to the bill amount, add or remove the difference one cent at a time, starting with the person with the most days on that bill (ties: alphabetical by name), cycling in that order. - People with 0 days on a bill owe nothing for it and are left out of that bill's shares. - net_usd = what the person paid minus the total of their shares (positive means they are owed money). Write `out/split.json`: `{"days": {"<bill_id>": {"<name>": <int>, ...}}, "shares": {"<bill_id>": {"<name>": <usd>, ...}}, "owed_usd": {"<name>": <usd>}, "net_usd": {"<name>": <usd>}}`. `owed_usd` and `net_usd` cover every housemate. ## 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.

Prorate six utility bills across 4-6 housemates who moved in and out on different dates, then work out what each owes and their net balance. Shares are rounded half-up to the cent, and a stated cent-by-cent rule makes each bill's shares add up exactly. Draws whose shares fall within 1e-4 of a half-cent tie are rejected. 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: occupancy_days prorated_shares shares_sum_to_bill zero_day_people_excluded owed_totals net_balances

Setup notes: Batch 16 case r05-shared-bills-split (offline, synthetic inputs, seed 2825218774). 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 0.27 (8 cores). Claude Code's own reported cost for claude-opus-5.5: $0.114168. 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.

Metrics

Estimated cost
$0.11
Wall time
19s
Human step-ins
0
Turns
3
Model usage
ModelInput tokOutput tokCost
AClaude Opus 5.5anthropic/claude-opus-5.5effort default (no --effort flag) · thinking on57,9561,668$0.11

Reproduce this run

  1. Use the use case prompt on the use case page.
  2. 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.
  3. It counts as a success only if it meets every success criterion: occupancy_days prorated_shares shares_sum_to_bill zero_day_people_excluded owed_totals net_balances
  4. 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

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Evidence log
[
 {
  "duration_api_ms": 17860,
  "stop_reason": "end_turn",
  "session_id": "[REDACTED]",
  "total_cost_usd": 0.1141678,
  "usage": {
   "input_tokens": 6,
   "cache_creation_input_tokens": 8871,
   "cache_read_input_tokens": 49079,
   "output_tokens": 1668,
   "output_tokens_details": {
    "thinking_tokens": 180
   },
   "server_tool_use": {
    "web_search_requests": 0,
    "web_fetch_requests": 0
   },
   "service_tier": "standard",
   "cache_creation": {
    "ephemeral_1h_input_tokens": 8871,
    "ephemeral_5m_input_tokens": 0
   },
   "inference_geo": "global",
   "iterations": [
    {
     "input_tokens": 2,
     "output_tokens": 619,
     "cache_read_input_tokens": 18908,
     "cache_creation_input_tokens": 2109,
     "cache_creation": {
      "ephemeral_5m_input_tokens": 0,
      "ephemeral_1h_input_tokens": 2109
     },
     "type": "message"
    }
   ],
   "speed": "standard",
   "fallback_credit": null
  },
  "modelUsage": {
   "claude-opus-5-5": {
    "inputTokens": 6,
    "outputTokens": 1668,
    "cacheReadInputTokens": 49079,
    "cacheCreationInputTokens": 8871,
    "webSearchRequests": 0,
    "costUSD": 0.1141678,
    "contextWindow": 1000000,
    "maxOutputTokens": 128000,
    "thinkingTokens": 180,
    "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": 3,
  "subtype": "success",
  "api_error_status": null,
  "result": "I wrote the split to `out/split.json`. Every bill's shares add up to exactly the bill amount, and the net amounts add up to $0.00. I also checked one rounding correction by hand (B04, below).\n\n| Housemate | Paid | Owes (`owed_usd`) | Net (`net_usd`) |\n|---|---|---|---|\n| Gus | $555.55 | $367.75 | **+$187.80** (is owed) |\n| Ivo | $406.30 | $348.41 | **+$57.89** (is owed) |\n| Eli | $357.10 | $367.75 | **\u2212$10.65** |\n| Jun | $331.53 | $367.75 | **\u2212$36.22** |\n| Femi | $0.00 | $198.82 | **\u2212$198.82** |\n\n- **Days:** Nobody has a move-out date, so everyone is counted through the end of each bill. Femi isn't on B01 at all because they moved in on 2026-08-14, after that bill's period ended.\n- **Rounding:** The one-cent corrections went to the right people. For example, on B04 the rounded shares came to $357.11, one cent over the bill. Eli, Gus, Ivo and Jun are tied on most days, so the cent came off Eli, first alphabetically, leaving Eli at $77.95 and the others at $77.96.\n\nThe script I used is at `/tmp/s/split.py`, outside the work folder. It uses exact decimal arithmetic so the half-up rounding isn't thrown off by floating-point error.",
  "ttft_ms": 2692,
  "type": "result",
  "duration_ms": 18202,
  "uuid": "[REDACTED]",
  "ttft_stream_ms": 1669,
  "time_to_request_ms": 234,
  "first_content_frame_ms": 1670,
  "queued_turn_count": 0,
  "result_index": 0
 }
]

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