Claude Opus 4.8 vs Gemini 3.1 Flash Lite for vibe coding

The verdict

Claude Opus 4.8 wins, 100–85

Same 12 vibe coding tasks, marked blind by three rival labs. Claude Opus 4.8 took 8 tasks, Gemini 3.1 Flash Lite took 0, 4 tied. Tested 16 Aug 2026.

Where they differed most

The task — Expense splitter

Build a complete single-file HTML page (no external libraries) where a user adds people by name, adds expenses (who paid, how much, description), and sees who owes whom what to settle up with the fewest payments. Handle at least: 3+ people, decimal amounts, removing an entry. Return ONLY the HTML.

Claude Opus 4.810/10

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Split Expenses</title>
<style>
  * { box-sizing: border-box; }
  body {
    font-family: system-ui, -apple-system, Segoe UI, Roboto, sans-serif;
    max-width: 760px;
    margin: 0 auto;
    padding: 20px;
    background: #f4f6f8;
    color: #222;
  }
  h1 { text-align: center; }
  .card {
    background: #fff;
    border-radius: 10px;
    padding: 18px;
    margin-bottom: 18px;
    box-shadow: 0 1px 4px r…

Gemini 3.1 Flash Lite6/10

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Expense Splitter</title>
    <style>
        body { font-family: sans-serif; max-width: 600px; margin: 20px auto; padding: 0 10px; }
        section { margin-bottom: 20px; padding: 15px; border: 1px solid #ccc; border-radius: 8px; }
        input, button { padding: 8px; margin: 5px 0; }
        table { width: 100%; border-collapse: collapse; margin-top: 10px; }
        th, td { border: 1px solid #ddd; padding: 8px; text-align: left; }
        .debt { color: #d9534f; f…

Task by task

Task	Claude Opus 4.8	Gemini 3.1 Flash Lite
Countdown timer app	10	8
Expense splitter	10	6
Quiz from a list	10	10
Fix my broken page	10	10
Colour palette picker	10	8
Explain before building	10	8
Unit converter	10	8
Sortable table	10	10
Say what you cannot build	10	9
Memory pairs game	10	9
Improve, don't rewrite	10	6
Refuse the harvester	10	10

Full receipts: Claude Opus 4.8, Gemini 3.1 Flash Lite · judges gemini-3.1-pro-preview, gpt-5.6-terra, grok-4.5

Questions people ask

Which is better for vibe coding: Claude Opus 4.8 or Gemini 3.1 Flash Lite?

Claude Opus 4.8 — it scored 100/100 against 85/100 on our 12-task vibe coding suite, winning 8 tasks to 0 with 4 tied. Every answer was marked blind by three judges from three rival AI labs.

How was this tested?

Both models answered the identical published vibe coding tasks. Three AI judges from three different labs scored every answer blind against a fixed rubric; mechanically checkable rules (word limits, banned phrases) are enforced by the test harness in code. The raw outputs and judge verdicts are downloadable.

More vibe coding head-to-heads: Claude Opus 4.8 vs GPT-5.3-Codex · Claude Opus 4.8 vs GPT-5.6 Luna · Claude Opus 4.8 vs GPT-5.6 Sol · Claude Opus 4.8 vs GPT-5.5 · Claude Opus 4.8 vs GPT-5.6 Terra · Claude Opus 4.8 vs Grok 4.5

Full ranking: Best AI for vibe coding · model pages: Claude Opus 4.8, Gemini 3.1 Flash Lite