Claude Haiku 5.5 (effort default (no --effort flag) · thinking on) on Implement a spec exactly, with nothing extra

AClaude Haiku 5.5default · thinking on · Claude Code 2.1.299 (headless -p) · cloud · 2026-10-16 · by @bobsiopener

Trust 80%Fully autonomoussuccess · first tryCompare

Estimated cost: $0.0029
Wall time: 9s
Human step-ins: 0
Outcome: Pass

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Exact prompt

Implement SPEC.md exactly. Then stop. Do not add anything the spec does not ask for.

Task prompt given to the agent (headless, offline, synthetic fixture inputs): Implement SPEC.md exactly. Then stop. Do not add anything the spec does not ask for. Inspired by https://x.com/mave99a/status/2096480295692460432 (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_flow; hidden test test_overwrite; under 60 non-blank lines; no classes; no extra files; stdlib only (no non-stdlib imports).

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 (6/6 checks).

Estimated cost List-price estimate; not actually billed.

Metrics

Estimated cost: $0.0029
Wall time: 9s
Human step-ins: 0
Turns: 4

Model usage
Model	Input tok	Output tok	Cost
AClaude Haiku 5.5anthropic/claude-haiku-5.5effort default (no --effort flag) · thinking on	77,888	1,359	$0.0029

Reproduce this run

Use the use case prompt on the use case page.
Same setup: Claude Haiku 5.5 (anthropic/claude-haiku-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: All automated rubric checks pass: hidden test test_flow; hidden test test_overwrite; under 60 non-blank lines; no classes; no extra files; stdlib only (no non-stdlib imports).
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

{
 "duration_api_ms": 7825,
 "stop_reason": "end_turn",
 "session_id": "[REDACTED]",
 "total_cost_usd": 0.0029270400000000005,
 "usage": {
  "input_tokens": 8,
  "cache_creation_input_tokens": 7726,
  "cache_read_input_tokens": 70154,
  "output_tokens": 1359,
  "output_tokens_details": {
   "thinking_tokens": 111
  },
  "server_tool_use": {
   "web_search_requests": 0,
   "web_fetch_requests": 0
  },
  "service_tier": "standard",
  "cache_creation": {
   "ephemeral_1h_input_tokens": 7726,
   "ephemeral_5m_input_tokens": 0
  },
  "inference_geo": "global",
  "iterations": [
   {
    "input_tokens": 2,
    "output_tokens": 266,
    "cache_read_input_tokens": 19852,
    "cache_creation_input_tokens": 413,
    "cache_creation": {
     "ephemeral_5m_input_tokens": 0,
     "ephemeral_1h_input_tokens": 413
    },
    "type": "message"
   }
  ],
  "speed": "standard",
  "fallback_credit": null
 },
 "modelUsage": {
  "claude-haiku-5-5": {
   "inputTokens": 8,
   "outputTokens": 1359,
   "cacheReadInputTokens": 70154,
   "cacheCreationInputTokens": 7726,
   "webSearchRequests": 0,
   "costUSD": 0.0029270400000000005,
   "contextWindow": 1000000,
   "maxOutputTokens": 128000,
   "thinkingTokens": 111,
   "canonicalModel": "claude-haiku-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": 4,
 "subtype": "success",
 "api_error_status": null,
 "result": "I implemented `SPEC.md` as `kv.py` in the work directory and stopped there.\n\nIt's a single file using only the Python 3 standard library, with 43 non-blank lines. It supports `set`, `get`, `del` and `list` against `kv.json` in the current directory, with the output and exit codes the spec gives.\n\nI smoke-tested it in a temporary directory: set, get, list, delete, and the `NOT FOUND` exit-1 cases all behaved as specified. The temporary directory was removed afterwards.\n\nThe spec doesn't cover a few cases, so I made these choices:\n- A missing `kv.json` is treated as an empty store.\n- Wrong arguments or an unknown command print a one-line usage message and exit 1.\n- `NOT FOUND` goes to stdout, like the other results.",
 "ttft_ms": 1374,
 "type": "result",
 "duration_ms": 8295,
 "uuid": "[REDACTED]",
 "ttft_stream_ms": 1219,
 "time_to_request_ms": 214,
 "first_content_frame_ms": 1220,
 "queued_turn_count": 0,
 "result_index": 0
}