# GPT-5.6 Luna vs Grok 4.20

> Side-by-side benchmark comparison for GPT-5.6 Luna and Grok 4.20 across agentic, coding, multimodal, knowledge, reasoning, multilingual, and math tasks.

- Canonical page: https://benchlm.ai/compare/gpt-5-6-luna-vs-grok-4-20-beta
- Last updated: September 24, 2026

- Shared sourced benchmarks: 10
- HTML indexing: indexable
- Ranking lane: BenchAlign v5.7

## Quick Verdict

Pick GPT-5.6 Luna if you want the stronger benchmark profile. Grok 4.20 only makes more sense when its price, context window, or workload-specific category wins matter more than the overall score.

## Summary

- GPT-5.6 Luna leads overall 65.6 to 59.66.
- The clearest category separation is in coding, where the averages are 64.5 for GPT-5.6 Luna and 23.8 for Grok 4.20.
- The biggest single benchmark swing is Terminal-Bench 2.1 (Vals) in Agentic, with scores of 79.0% and 44.2%.
- GPT-5.6 Luna is the cheaper option on output tokens, which matters if you expect large responses or heavy interactive use.
- Grok 4.20 also has the larger context window at 2M.

## Model Snapshot

| Property | GPT-5.6 Luna | Grok 4.20 |
|----------|----------|----------|
| Creator | OpenAI | xAI |
| Type | Proprietary | Proprietary |
| Reasoning | Reasoning | Reasoning |
| Context | 1.05M | 2M |
| Overall Score | 65.6 | 59.66 |
| Benchmarks Covered | 29 | 23 |
| Pricing (input/output) | $0.20 / $1.20 | $1.25 / $2.50 |

## Category Breakdown

### Agentic

- Winner: GPT-5.6 Luna
- GPT-5.6 Luna public-lane score: 55.3 (Supported · #28/105)
- Grok 4.20 public-lane score: 24.5 (Supported · #81/105)

| Benchmark | GPT-5.6 Luna | Grok 4.20 | Winner |
|-----------|-----------|-----------|--------|
| Terminal-Bench 3.0 | 14.3% | Coming soon | Coming soon |
| Terminal-Bench 2.1 | 84.7% | Coming soon | Coming soon |
| BrowseComp | 83.3% | Coming soon | Coming soon |
| OSWorld 2.0 | 45.6% | Coming soon | Coming soon |
| CyberGym | 77.9% | Coming soon | Coming soon |
| ExploitGym | 12.4% | Coming soon | Coming soon |
| Toolathlon | 53.4% | Coming soon | Coming soon |
| Terminal-Bench 2.1 (Vals) | 79.0% | 44.2% | GPT-5.6 Luna |
| ApprenticeBench | 7% | Coming soon | Coming soon |
| Terminal-Bench 2.0 | Coming soon | 47.1% | Coming soon |
| DeepSearchQA | Coming soon | 62.8% | Coming soon |
| Gert Labs | Coming soon | 38.36% | Coming soon |

### Coding

- Winner: GPT-5.6 Luna
- GPT-5.6 Luna public-lane score: 64.5 (Supported · #9/135)
- Grok 4.20 public-lane score: 23.8 (Supported · #106/135)

| Benchmark | GPT-5.6 Luna | Grok 4.20 | Winner |
|-----------|-----------|-----------|--------|
| SWE-bench Pro | 62.7% | 51.8% | GPT-5.6 Luna |
| Terminal-Bench 2.1 | 84.7% | Coming soon | Coming soon |
| DeepSWE | 67.2% | Coming soon | Coming soon |
| FrontierCode 1.1 Extended | 55.1% | Coming soon | Coming soon |
| cursorBench32 | 61.1% | Coming soon | Coming soon |
| VulcanBench v3 | 85.5% | Coming soon | Coming soon |
| SWE-bench (Vals) | 93.0% | 72.2% | GPT-5.6 Luna |
| LiveCodeBench Pro | Coming soon | 74.2% | Coming soon |
| SWE-bench Verified | Coming soon | 76.7% | Coming soon |
| Vibe Code Bench | Coming soon | 4.06% | Coming soon |
| LiveCodeBench (Vals) | Coming soon | 84.3% | Coming soon |

### Reasoning

- Winner: Not comparable
- GPT-5.6 Luna public-lane score: 54.7 (#18/19)
- Grok 4.20 public-lane score: 41.1 (Unranked · 2 rankable rows)

| Benchmark | GPT-5.6 Luna | Grok 4.20 | Winner |
|-----------|-----------|-----------|--------|
| ARC-AGI-2 | 59.5% | 53.3% | GPT-5.6 Luna |
| ARC-AGI-3 | 0.2% | 0.1% | GPT-5.6 Luna |

### Multimodal & Grounded

- Winner: Directional only
- GPT-5.6 Luna public-lane score: 67.1 (#22/50)
- Grok 4.20 public-lane score: 34.6 (#45/50)

| Benchmark | GPT-5.6 Luna | Grok 4.20 | Winner |
|-----------|-----------|-----------|--------|
| MMMU-Pro | 78.4% | 75.2% | GPT-5.6 Luna |
| MMMU-Pro w/ Python | 79.5% | Coming soon | Coming soon |
| CharXiv | Coming soon | 60.9% | Coming soon |
| ERQA | Coming soon | 54.1% | Coming soon |
| SimpleVQA | Coming soon | 57.4% | Coming soon |
| MedXpertQA (MM) | Coming soon | 65.8% | Coming soon |

### Knowledge

- Winner: GPT-5.6 Luna
- GPT-5.6 Luna public-lane score: 64.6 (Supported · #22/158)
- Grok 4.20 public-lane score: 51 (Supported · #55/158)

| Benchmark | GPT-5.6 Luna | Grok 4.20 | Winner |
|-----------|-----------|-----------|--------|
| GPQA | 92.3% | Coming soon | Coming soon |
| GPQA-D | 92.3% | 88.5% | GPT-5.6 Luna |
| HealthBench Professional | 55.7% | Coming soon | Coming soon |
| HealthBench Hard | 32.0% | 20.3% | GPT-5.6 Luna |
| GPQA Diamond (Vals) | 91.7% | 88.6% | GPT-5.6 Luna |
| MMLU-Pro (Vals) | 86.0% | 86.3% | Grok 4.20 |
| HLE w/o tools | Coming soon | 31.6% | Coming soon |
| MedXpertQA (Text) | Coming soon | 50.2% | Coming soon |

### Mathematics

- Winner: Not comparable
- GPT-5.6 Luna public-lane score: 94.2 (Unranked · 3 rankable rows)
- Grok 4.20 public-lane score: Coming soon

| Benchmark | GPT-5.6 Luna | Grok 4.20 | Winner |
|-----------|-----------|-----------|--------|
| FrontierMath (legacy) | 78.6% | Coming soon | Coming soon |
| FrontierMath v2 (Tiers 1-3) | 78.600% | Coming soon | Coming soon |
| FrontierMath v2 (Tier 4) | 58.500% | Coming soon | Coming soon |

## FAQ

### Which is better overall, GPT-5.6 Luna or Grok 4.20?

GPT-5.6 Luna is ahead overall on BenchLM right now.

### Where is the biggest gap between GPT-5.6 Luna and Grok 4.20?

The widest category gap is in coding, where the averages are 64.5 for GPT-5.6 Luna and 23.8 for Grok 4.20.

### How many benchmarks does GPT-5.6 Luna cover on BenchLM?

GPT-5.6 Luna currently has 29 sourced benchmark scores on BenchLM.

### How many benchmarks does Grok 4.20 cover on BenchLM?

Grok 4.20 currently has 23 sourced benchmark scores on BenchLM.

## Related Comparisons

- [GPT-5.6 Luna vs GPT-5.6 Sol](/compare/gpt-5-6-luna-vs-gpt-5-6-sol)
- [Grok 4.20 vs GPT-5.6 Sol](/compare/gpt-5-6-sol-vs-grok-4-20-beta)
- [GPT-5.6 Luna vs GPT-5.6 Terra](/compare/gpt-5-6-luna-vs-gpt-5-6-terra)
- [Grok 4.20 vs GPT-5.6 Terra](/compare/gpt-5-6-terra-vs-grok-4-20-beta)

## Explore More

- [GPT-5.6 Luna profile](/models/gpt-5-6-luna)
- [Grok 4.20 profile](/models/grok-4-20-beta)
- [Compare Pricing](/llm-pricing)
- [Alternative Finder](/tools/alternative-finder)
- [LLM Selector](/tools/llm-selector)
- [Overall Rankings](/best/overall)