Claude Sonnet 5.5 (effort default (no --effort flag) · thinking on) on Pick the real root cause of an outage from a call graph, a change log and two hours of error logs

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

Trust 80%Fully autonomoussuccess · first tryCompare

Estimated cost: $0.06
Wall time: 14s
Human step-ins: 0
Outcome: Pass

Compare with other models on this task →

Exact prompt

# Find the root cause of last night's outage Inputs: `services.json` (which service calls which), `changes.json` (every deploy, config change and certificate rotation in the period), `errors.log` (one line per logged error, 02:00-04:00 UTC), `alert.json` (when the page fired). Definitions: - The baseline hour is 02:00-02:59 UTC and the incident window is 03:00-03:59 UTC. A service's baseline peak is its highest count of ERROR lines in any single baseline minute. - A service's onset is the first incident-window minute in which its ERROR count exceeds its baseline peak + 5. A service with no onset is unaffected. - The origin service is the affected service with the earliest onset whose onset is not preceded by the onset of a service it calls (directly or indirectly). If several qualify, the one with the earliest onset is the origin. - The root cause is the latest change to the origin service made at or before its onset minute. - For every other change, give the reason it is ruled out: "after_onset" (it happened after the origin's onset), "unaffected_service" (its service never had an onset), or "not_origin" (its service was affected, but only as a consequence of the origin). Write `out/rca.json`: `{"root_cause_change": "<change_id>", "origin_service": "<name>", "onset_utc": "HH:MM", "affected_services": [<sorted>], "ruled_out": {"<change_id>": "<reason>", ...}}`. ## 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.

Find the origin of a cascading outage among 8-11 services: baseline-adjusted onsets from about 2,000 error lines, then the origin service whose onset no dependency's onset precedes, then the latest change to it before onset. Plausible decoys include a hotfix deployed just before the page fired, a change on a chronically noisy service, a mid-chain deploy and a later certificate rotation. Each change must also be ruled out with the right reason. 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). Folder-restore note: this run's output files under work/out/ were lost in a 1:22 AM ET restore on Oct 21, 2026. The trace, step-in exchanges and output-hash list were checked against the recorded SHA-256 values and match; the hashes of the individual output files inside that list can no longer be recomputed. Measured data unchanged.

Success criteria: root_cause origin_service onset_minute affected_services alert_adjacent_deploy_ruled_out all_ruled_out_reasons

Setup notes: Batch 18 case t03-root-cause-from-logs (offline, synthetic inputs, seed 431618348). 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 0.16 (8 cores). Time-zone results depend on the system time-zone database: tzdata 2026c-0+deb13u1 (Python zoneinfo). Inputs for this case cannot be replayed from the seed (generator nondeterminism found 2026-10-20); score stands as measured. Claude Code's own reported cost for claude-sonnet-5.5: $0.055333. 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: $0.06
Wall time: 14s
Human step-ins: 0
Turns: 4

Model usage
Model	Input tok	Output tok	Cost
AClaude Sonnet 5.5anthropic/claude-sonnet-5.5effort default (no --effort flag) · thinking on	78,833	1,554	$0.06

Reproduce this run

Use the use case prompt on the use case page.
Same setup: Claude Sonnet 5.5 (anthropic/claude-sonnet-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: root_cause origin_service onset_minute affected_services alert_adjacent_deploy_ruled_out all_ruled_out_reasons
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": 12648,
  "stop_reason": "end_turn",
  "session_id": "[REDACTED]",
  "total_cost_usd": 0.0553327,
  "usage": {
   "input_tokens": 8,
   "cache_creation_input_tokens": 8178,
   "cache_read_input_tokens": 70647,
   "output_tokens": 1554,
   "output_tokens_details": {
    "thinking_tokens": 362
   },
   "server_tool_use": {
    "web_search_requests": 0,
    "web_fetch_requests": 0
   },
   "service_tier": "standard",
   "cache_creation": {
    "ephemeral_1h_input_tokens": 8178,
    "ephemeral_5m_input_tokens": 0
   },
   "inference_geo": "global",
   "iterations": [
    {
     "input_tokens": 2,
     "output_tokens": 450,
     "cache_read_input_tokens": 20070,
     "cache_creation_input_tokens": 647,
     "cache_creation": {
      "ephemeral_5m_input_tokens": 0,
      "ephemeral_1h_input_tokens": 647
     },
     "type": "message"
    }
   ],
   "speed": "standard",
   "fallback_credit": null
  },
  "modelUsage": {
   "claude-sonnet-5-5": {
    "inputTokens": 8,
    "outputTokens": 1554,
    "cacheReadInputTokens": 70647,
    "cacheCreationInputTokens": 8178,
    "webSearchRequests": 0,
    "costUSD": 0.0553327,
    "contextWindow": 1000000,
    "maxOutputTokens": 128000,
    "thinkingTokens": 362,
    "canonicalModel": "claude-sonnet-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 wrote `out/rca.json`. The root cause is CHG-6991, the orders deploy at 03:02:41 (\"rotate TLS certificate\").\n\nOrders is the origin service, with its onset at 03:08. It calls no other service, so no earlier onset could have caused it. Six services were affected, with these onsets:\n\n| Service | Onset (UTC) |\n|---|---|\n| orders | 03:08 |\n| ledger | 03:11 |\n| catalog | 03:13 |\n| payments | 03:13 |\n| api | 03:15 |\n| edge | 03:16 |\n\nDb-main, auth and cache never crossed their threshold. Cache's baseline peak was 7 errors in a minute, so it needed 13 or more to count.\n\nReasons given for the other changes:\n- **CHG-8981** (catalog, 03:06): `not_origin`, since catalog was affected only as a consequence of orders.\n- **CHG-6074** (edge, 03:17): `after_onset`.\n- **CHG-3547** (auth) and **CHG-2118** (cache): `unaffected_service`.\n- **CHG-5576** (orders, 02:39): I labelled this `superseded`, which is not one of the three reasons you listed. It is an orders change before the onset, but CHG-6991 is the later one. If the check only accepts your three values, this one entry will fail.",
  "ttft_ms": 1767,
  "type": "result",
  "duration_ms": 13070,
  "uuid": "[REDACTED]",
  "ttft_stream_ms": 960,
  "time_to_request_ms": 256,
  "first_content_frame_ms": 961,
  "queued_turn_count": 0,
  "result_index": 0
 }
]