# VulcanBench Coding Intelligence Index v1 (VulcanBench CII v1)

> A post-cutoff software-engineering benchmark with hidden functional tests and regression guards, reported for vendor coding-agent harnesses.

Canonical page: https://benchlm.ai/benchmarks/vulcanciiv1

- Category: [Coding](/coding)
- Last updated: October 17, 2026

## About VulcanBench CII v1

- Year: 2026
- Tasks: 38 validated post-cutoff repository tasks
- Format: Pass@1 with vendor coding-agent harnesses
- Difficulty: Mid-band frontier software engineering
- Paper: [CII v1 frontier results](https://github.com/morganlinton/VulcanBench/blob/main/docs/results/cii-v1-2026-08/README.md)

CII v1 contains 38 validated tasks from pull requests merged between May and August 2026. The published snapshot measures 37 tasks for Claude Opus 5 with Claude Code CLI and GPT-5.6 Sol with Codex CLI. These are model-plus-vendor-harness results, so we keep them display-only and preserve uncertainty, functional score, task count, and run count in the source snapshot.

VulcanBench CII v1 is currently displayed on BenchLM for reference, but it is excluded from the weighted scoring formula.

## Leaderboard (3 models)

| Rank | Model | Creator | Score |
|------|-------|---------|-------|
| 1 | [Claude Opus 5](/models/claude-opus-5) | Anthropic | 96.4% |
| 2 | [Claude Sonnet 5](/models/claude-sonnet-5) | Anthropic | 89.2% |
| 3 | [GPT-5.6 Sol](/models/gpt-5-6-sol) | OpenAI | 86.5% |

## FAQ

### What does VulcanBench CII v1 measure?

A post-cutoff software-engineering benchmark with hidden functional tests and regression guards, reported for vendor coding-agent harnesses.

### Which model scores highest on VulcanBench CII v1?

Claude Opus 5 by Anthropic currently leads with a score of 96.4% on VulcanBench CII v1.

### How many models are evaluated on VulcanBench CII v1?

3 AI models have published results on VulcanBench CII v1 in the BenchLM catalog.

### Does VulcanBench CII v1 affect BenchLM's overall score?

Not directly. VulcanBench CII v1 is still displayed on BenchLM for reference, but it is excluded from the weighted scoring formula.

## Compare Top Models on VulcanBench CII v1

- [Claude Opus 5 vs Claude Sonnet 5](/compare/claude-opus-5-vs-claude-sonnet-5)
- [Claude Sonnet 5 vs GPT-5.6 Sol](/compare/claude-sonnet-5-vs-gpt-5-6-sol)