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Tool call · 5 checks · max 400 tokens · benched 2026-09-16

Gemini 3.1 Pro Preview vs Gemini 3.8 Flash vs Gemini 3.5 Flash Lite on emit a weather tool call

Google models side by side on "Emit a weather tool call": Gemini 3.5 Flash Lite scores 10/10; Gemini 3.5 Flash Lite is the cheapest answer scoring 8+ at $0.09 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": "get_weather", "parameters": {"city": "string", "unit": "one of 'c' or 'f'"}}

Produce the tool call for this user message as a JSON object of the shape {"name": string, "arguments": object}.

User: What's it like in Lisbon right now? Fahrenheit please.

Rubric for the judge: Exactly {"name":"get_weather","arguments":{"city":"Lisbon","unit":"f"}} with no extra keys or text.

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.

Gemini 3.1 Pro Preview

google/gemini-3.1-pro-preview

10/10
Latency
2.5s
Cost
$0.00307
Per 1,000
$3.07

99 in · 239 out (200 reasoning) · 11 words · checks 5/5

  • json_valid
  • json_keys
  • regex
  • regex
  • regex
{
  "name": "get_weather",
  "arguments": {
    "city": "Lisbon",
    "unit": "f"
  }
}

Judge: Output exactly matches the required format with correct tool name, city parameter, and unit parameter, with no extra keys or commentary.

Gemini 3.8 Flash

google/gemini-3.8-flash

10/10
Latency
2.3s
Cost
$0.00016
Per 1,000
$0.16

99 in · 24 out · 7 words · checks 5/5

  • json_valid
  • json_keys
  • regex
  • regex
  • regex
{"name": "get_weather", "arguments": {"city": "Lisbon", "unit": "f"}}

Judge: Output exactly matches the required format with correct tool name, city, and unit parameters, no extra keys or commentary.

Gemini 3.5 Flash Lite

google/gemini-3.5-flash-lite

10/10
top judge scorecheapest scoring 8+
Latency
635ms
Cost
$9.0e-5
Per 1,000
$0.09

99 in · 24 out · 7 words · checks 5/5

  • json_valid
  • json_keys
  • regex
  • regex
  • regex
{"name": "get_weather", "arguments": {"city": "Lisbon", "unit": "f"}}

Judge: Output exactly matches the required format with correct tool name, city, and unit parameters, no extra keys or commentary.

Frequently asked

What does this prompt test?

Tool call: Exactly {"name":"get_weather","arguments":{"city":"Lisbon","unit":"f"}} with no extra keys or text. The deterministic checks are json_valid, json_keys, regex, regex, regex.

Which model should I pick for this task?

If the judge's bar of 8/10 is good enough for you, Gemini 3.5 Flash Lite at $0.09 per 1,000 runs. If you need the top score, Gemini 3.5 Flash Lite at $0.09 per 1,000 runs.

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