Claude Opus 5 vs Claude Sonnet 5 vs Claude Sonnet 4.6 vs Claude Haiku 4.5 on emit a calendar tool call
Anthropic models side by side on "Emit a calendar tool call": Claude Haiku 4.5 scores 10/10; Claude Haiku 4.5 is the cheapest answer scoring 8+ at $0.60 per 1,000 runs. Outputs, checks, judge reasons, latency and cost.
The prompt every model received
System
You are a function-calling engine. Reply with JSON only, no prose, no code fences.
User
You have one tool:
{"name": "create_event", "parameters": {"title": "string", "start": "ISO 8601 date-time without timezone, e.g. 2026-01-31T09:00", "duration_minutes": "integer", "attendees": "array of email strings"}}
Produce the tool call for this user message as a JSON object of the shape {"name": string, "arguments": object}.
User: Book a 45-minute design review with [email protected] and [email protected] on 2 October 2026 at 3pm.
Rubric for the judge: Correct tool name, ISO start 2026-10-02T15:00, integer duration 45, both attendees in an array, a sensible title.
Side by side
Every cell is one OpenRouter call at temperature 0 with the prompt's token cap and reasoning effort "low" where the model supports it. Cost is usage × the catalogue rate in models.json. Quality is one judge call to anthropic/claude-haiku-4.5 against the prompt's rubric, cached per prompt version.
Judge: All rubric criteria met: correct tool name, proper ISO 8601 start datetime, integer duration of 45 minutes, both attendees in array format, and sensible title.
Judge: All rubric criteria met: correct tool name, proper ISO 8601 start datetime, integer duration of 45 minutes, both attendees in array format, and sensible title.
Judge: All rubric criteria met: correct tool name, proper ISO 8601 start datetime, integer duration of 45 minutes, both attendees in array format, and sensible title.
Judge: All rubric requirements met: correct tool name, ISO start datetime 2026-10-02T15:00, integer duration 45, both attendees in array, and sensible title 'Design Review'.
Frequently asked
▸What does this prompt test?
Tool call: Correct tool name, ISO start 2026-10-02T15:00, integer duration 45, both attendees in an array, a sensible title. The deterministic checks are json_valid, json_keys, regex, contains, regex, contains, contains.
▸Which model should I pick for this task?
If the judge's bar of 8/10 is good enough for you, Claude Haiku 4.5 at $0.60 per 1,000 runs. If you need the top score, Claude Haiku 4.5 at $0.60 per 1,000 runs.
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