# Claude Sonnet 5.5 vs GPT-5.1-Codex

> Claude Sonnet 5.5 is the stronger model overall, scoring 60.5 to 38.2 on the Noometry Index.

- Canonical page: https://noometry.com/compare/claude-sonnet-5-5-vs-gpt-5-1-codex
- Last updated: 2026-10-10
- Shared benchmarks: 3

## Summary

- They share 3 benchmarks with published results for both. Claude Sonnet 5.5 scores higher in 3 categories and GPT-5.1-Codex in 0 categories; 3 gaps are clear of the uncertainty.
- The widest gap is in math, where Claude Sonnet 5.5 leads 88.7 to 29.3.
- The biggest single-benchmark swing is ProofBench: 100% for Claude Sonnet 5.5 and 9% for GPT-5.1-Codex.
- GPT-5.1-Codex is cheaper at $1.25 / $10 per million input/output tokens, against $2 / $10 for Claude Sonnet 5.5.
- Claude Sonnet 5.5 accepts more context: 1M tokens versus 400K.

## Snapshot

| | Claude Sonnet 5.5 | GPT-5.1-Codex |
|---|---|---|
| Provider | Anthropic | OpenAI |
| Noometry Index | 60.5 | 38.2 |
| Rank | 10 | 178 |
| Context | 1M | 400K |
| Input $/M | $2 | $1.25 |
| Output $/M | $10 | $10 |
| Weights | Proprietary | Proprietary |

## Coding

- Claude Sonnet 5.5: 65.5 (#6)
- GPT-5.1-Codex: 41.7 (#107)

| Benchmark | Claude Sonnet 5.5 | GPT-5.1-Codex |
|---|---|---|
| LMArena WebDev | 1699 | 1337 |
| ALE-Bench | 1,819 | 1,245 |
| FrontierCode | 52.1% | — |
| SWE-bench Verified (bash only) | — | 66% |
| CursorBench | 55.5% | — |
| FrontierSWE | 61.9% | — |
| SciCode | 61% | — |

## Agentic & Tool Use

- Claude Sonnet 5.5: 44.9 (#14)
- GPT-5.1-Codex: 37.8 (#32)

| Benchmark | Claude Sonnet 5.5 | GPT-5.1-Codex |
|---|---|---|
| Terminal-Bench | — | 60.4% |
| APEX-Agents | 75.5% | — |
| METR Time Horizons | — | 70.8% |

## Reasoning

- Claude Sonnet 5.5: 52.4 (#29)
- GPT-5.1-Codex: —

| Benchmark | Claude Sonnet 5.5 | GPT-5.1-Codex |
|---|---|---|
| CritPt | 31.4% | — |
| Mystery Game Puzzles | 65% | — |

## Math

- Claude Sonnet 5.5: 88.7 (#4)
- GPT-5.1-Codex: 29.3 (#218)

| Benchmark | Claude Sonnet 5.5 | GPT-5.1-Codex |
|---|---|---|
| ProofBench | 100% | 9% |
| FrontierMath (Tiers 1-3) | 88.8% | — |
| FrontierMath Tier 4 | 80.5% | — |
| OTIS Mock AIME 2024-2025 | 100% | — |

## Knowledge

- Claude Sonnet 5.5: 66.0 (#11)
- GPT-5.1-Codex: —

| Benchmark | Claude Sonnet 5.5 | GPT-5.1-Codex |
|---|---|---|
| GPQA Diamond | 95.6% | — |
| SimpleQA Verified | 46.5% | — |

## Multimodal

- Claude Sonnet 5.5: 53.2 (#5)
- GPT-5.1-Codex: —

| Benchmark | Claude Sonnet 5.5 | GPT-5.1-Codex |
|---|---|---|
| Furniture Assembly | 75% | — |

## FAQ

### Is Claude Sonnet 5.5 better than GPT-5.1-Codex?

Claude Sonnet 5.5 is the stronger model overall, scoring 60.5 to 38.2 on the Noometry Index.

### Which is cheaper, Claude Sonnet 5.5 or GPT-5.1-Codex?

GPT-5.1-Codex is cheaper. It lists at $1.25 per million input tokens and $10 per million output tokens; Claude Sonnet 5.5 lists at $2 and $10.

### Is Claude Sonnet 5.5 or GPT-5.1-Codex better for coding?

Claude Sonnet 5.5 scores higher on coding benchmarks: 65.5 versus 41.7 in the Noometry coding category.

### Which has the bigger context window?

Claude Sonnet 5.5 does, with 1M tokens against 400K.

### How many benchmarks do Claude Sonnet 5.5 and GPT-5.1-Codex share?

3 benchmarks have published results for both models. Claude Sonnet 5.5 has 16 scored results on Noometry and GPT-5.1-Codex has 6.