Claude Opus 5.5 on Fix three bugs in a Python repo so its tests pass

AClaude Opus 5.5 · Claude Code 2.1.299 (headless -p) · cloud · 2026-10-14 · by @bobsiopener

Trust 80%Fully autonomoussuccess · first tryCompare

Estimated cost: $0.08
Wall time: 10s
Human step-ins: 0
Outcome: Pass

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Exact prompt

You are working on the repository in ./repo. Fix the three bugs described in repo/ISSUES.md in textstats.py. Run the existing tests (python3 -m unittest in repo) and make sure they pass. Do not change function names or signatures.

Task prompt given to the agent (headless, offline, synthetic fixture inputs): You are working on the repository in ./repo. Fix the three bugs described in repo/ISSUES.md in textstats.py. Run the existing tests (python3 -m unittest in repo) and make sure they pass. Do not change function names or signatures. Inspired by https://x.com/bnjmn_marie/status/2089775546943312076 (unverified; not checked with the author). This is an independent re-run on a reproducible synthetic task; it does not report or reproduce the original post's numbers. Cost shown is a list-price API-equivalent estimate (run on a Claude Pro subscription, not billed).

Success criteria: All automated rubric checks pass: hidden test test_avg; hidden test test_mc; hidden test test_wc.

Setup notes: Cost is an ESTIMATE: Claude Code's list-price API-equivalent figure. The run used a Claude Pro subscription, so nothing was billed. input_tokens = all input incl. cache-creation and cache-read tokens; cached_tokens = cache reads (subset of input). Claude Code's cost bills cache writes at the 1h cache-write premium, so it can differ from a flat input-price recompute. Web disabled; tools Read/Write/Edit/Glob/Grep/Bash; single run; scored automatically (3/3 checks).

Estimated cost List-price estimate; not actually billed.

Metrics

Estimated cost: $0.08
Wall time: 10s
Human step-ins: 0
Turns: 4

Model usage
Model	Input tok	Output tok	Cost
AClaude Opus 5.5anthropic/claude-opus-5.5	54,410	870	$0.08

Reproduce this run

Use the use case prompt on the use case page.
Same setup: Claude Opus 5.5 (anthropic/claude-opus-5.5) via Claude Code 2.1.299 (headless -p), cloud.
It counts as a success only if it meets every success criterion: All automated rubric checks pass: hidden test test_avg; hidden test test_mc; hidden test test_wc.
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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 "result": "I fixed all three bugs in `textstats.py`, and the 3 existing tests pass with `python3 -m unittest`.\n\n1. **`word_count`** now splits on any run of whitespace instead of on single spaces. `\"hello   world\"` gives 2, tabs and newlines count as separators, and an empty string gives 0.\n2. **`avg_word_length`** returns `0.0` when the text has no words instead of crashing.\n3. **`most_common`** lowercases the text before counting, so \"The\", \"the\" and \"THE\" count as one word. When two words have the same count it returns the one that comes first alphabetically, and it returns `None` for empty text.\n\nI also checked a few edge cases by hand: tabs and newlines, empty strings, and a tie (`most_common(\"b a B A c\")` returns `\"a\"`). The tie-break and the `None` result aren't covered by the existing tests. Function names and signatures are unchanged.",
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