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Claude Sonnet 5.5 (effort default (no --effort flag) · thinking off) on Rebuild two years of a repayment mortgage statement with a rate change, overpayments and a bounced payment

AClaude Sonnet 5.5default · thinking off · Claude Code 2.1.299 (headless -p) · cloud · 2026-10-21 · by @bobsiopener

Trust 80%Fully autonomoussuccess · first try
Estimated cost
$0.05
Wall time
13s
Human step-ins
0
Outcome
Pass

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Summary

Exact prompt

# Rebuild a mortgage statement Inputs: `loan.json` (opening balance on 2024-11-01, starting annual rate, contractual monthly payment), `rate-notices.csv` (rate changes) and `payments.csv` (everything that hit the mortgage account, including returned direct debits). Rebuild the 24 monthly statements from November 2024 to October 2026. - Each month: interest = opening balance x annual rate / 12, rounded to the penny half-up, and added to the balance. Then every payment for that month that was not returned comes off the balance. - A rate notice applies from the month in its `effective_month` (that month's interest already uses the new rate). - A payment whose `status` is `returned` never reached the lender; ignore it. Overpayments are payments like any other. - Keep the balance in exact pence; there is no other rounding. Write `out/statement.json`: `{"closing_balance": <balance after October 2026>, "total_interest": <sum of the 24 monthly interest charges>, "interest_by_year": {"2024": <...>, "2025": <...>, "2026": <...>}, "total_paid": <sum of payments counted>, "interest_after_rate_change": <interest charged from the first rate-change month onwards>}`. ## 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.

Rebuild 24 months of a repayment mortgage from the loan terms, a payment log and the lender's rate notices. Interest is charged monthly on the opening balance and rounded to the penny each month, a rate change applies from its stated month, overpayments come straight off the balance, and a returned direct debit has to be ignored. Rounding only at the end, missing the rate change or counting the bounced payment each changes the closing balance. 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: closing_balance monthly_penny_rounding rate_change returned_payment

Setup notes: Batch 22 case x01-loan-statement-overpayments (offline, synthetic inputs, seed 105819659). 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 0.95 (8 cores). 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: $0.048779. Score: 4/4. 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
$0.05
Wall time
13s
Human step-ins
0
Turns
4
Model usage
ModelInput tokOutput tokCost
AClaude Sonnet 5.5anthropic/claude-sonnet-5.5effort default (no --effort flag) · thinking off76,1521,262$0.05

Reproduce this run

  1. Use the use case prompt on the use case page.
  2. Same setup: Claude Sonnet 5.5 (anthropic/claude-sonnet-5.5, effort default (no --effort flag) · thinking off) via Claude Code 2.1.299 (headless -p), cloud.
  3. It counts as a success only if it meets every success criterion: closing_balance monthly_penny_rounding rate_change returned_payment
  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
[
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  "total_cost_usd": 0.04877889999999999,
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   "output_tokens_details": {
    "thinking_tokens": 0
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   "server_tool_use": {
    "web_search_requests": 0,
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   "service_tier": "standard",
   "cache_creation": {
    "ephemeral_1h_input_tokens": 7315,
    "ephemeral_5m_input_tokens": 0
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   "inference_geo": "global",
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      "ephemeral_5m_input_tokens": 0,
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     "type": "message"
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   "speed": "standard",
   "fallback_credit": null
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  "modelUsage": {
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    "contextWindow": 1000000,
    "maxOutputTokens": 128000,
    "thinkingTokens": 0,
    "canonicalModel": "claude-sonnet-5-5",
    "provider": "firstParty",
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  },
  "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,
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   "killed": {
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    "user": 0,
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   "refused": {
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  "safety_stops": 0,
  "is_error": false,
  "num_turns": 4,
  "subtype": "success",
  "api_error_status": null,
  "result": "I rebuilt the 24 statements and wrote the results to `out/statement.json`. I haven't checked the figures against any other source.\n\n| Field | Value |\n|---|---|\n| `closing_balance` | 135,748.30 |\n| `total_interest` | 10,619.98 |\n| `interest_by_year` | 2024: 1,088.74; 2025: 5,711.25; 2026: 3,819.99 |\n| `total_paid` | 43,032.75 |\n| `interest_after_rate_change` | 5,815.72 |\n\n- **Returned debit:** The returned direct debit on 2026-06-03 is excluded. The card payment of the same amount on 2026-06-14 is counted, so June 2026 has one payment of 1,007.59.\n- **Overpayments:** The three overpayments (May 2025, June 2025, August 2026) are counted like any other payment.\n- **Rate change:** The one notice drops the rate from 3.89% to 3.14%, effective August 2025. That month's interest already uses 3.14%, and `interest_after_rate_change` sums the interest from August 2025 through October 2026.\n\nI used exact decimal arithmetic, with interest rounded half-up to the penny each month.",
  "ttft_ms": 2041,
  "type": "result",
  "duration_ms": 12311,
  "uuid": "[REDACTED]",
  "ttft_stream_ms": 1590,
  "time_to_request_ms": 306,
  "first_content_frame_ms": 1590,
  "queued_turn_count": 0,
  "result_index": 0
 }
]

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