Model comparison
Claude Sonnet 5.5 vs GPT-5.1-Codex
Claude Sonnet 5.5 is the stronger model overall, scoring 61.9 to 38.6 on the Noometry Index.
Last verified . 3 shared benchmarks.
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 87.9 to 30.3.
- 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.
Side by side
| Claude Sonnet 5.5 | GPT-5.1-Codex | |
|---|---|---|
| Provider | Anthropic | OpenAI |
| Noometry Index | 61.9 | 38.6 |
| Released | 2026-09-28 | 2025-11-12 |
| Weights | Proprietary | Proprietary |
| Context window | 1M | 400K |
| Max output | 128K | 128K |
| Input $ / M tokens | $2 | $1.25 |
| Output $ / M tokens | $10 | $10 |
| Results tracked | 32 | 6 |
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Category by category
Coding Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 67.3 (#6), GPT-5.1-Codex: 41.9 (#116)
| Benchmark | Claude Sonnet 5.5 | GPT-5.1-Codex |
|---|---|---|
| LMArena WebDev | 1774 | 1337 |
| ALE-Bench | 1,819 | 1,245 |
| FrontierCode | 52.1% | — |
| SWE-bench Verified (bash only) | — | 66% |
| CursorBench | 55.5% | — |
| FrontierSWE | 61.9% | — |
| SciCode | 61% | — |
| LMArena Coding | 1513 | — |
Agentic & Tool Use Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 45.0 (#16), GPT-5.1-Codex: 38.0 (#33)
| Benchmark | Claude Sonnet 5.5 | GPT-5.1-Codex |
|---|---|---|
| Terminal-Bench | — | 60.4% |
| APEX-Agents | 75.5% | — |
| METR Time Horizons | — | 70.8% |
Reasoning Not comparable
Claude Sonnet 5.5: 54.0 (#28), GPT-5.1-Codex: —
| Benchmark | Claude Sonnet 5.5 | GPT-5.1-Codex |
|---|---|---|
| NYT Connections (extended) | 80.5% | — |
| CritPt | 31.4% | — |
| LMArena Hard Prompts | 1495 | — |
| Mystery Game Puzzles | 65% | — |
| Epoch Capabilities Index | 165.03 | — |
Math Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 87.9 (#6), GPT-5.1-Codex: 30.3 (#235)
| 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% | — |
| LMArena Math | 1510 | — |
| FrontierMath Erdős | 2.9% | — |
Knowledge Not comparable
Claude Sonnet 5.5: 66.0 (#12), GPT-5.1-Codex: —
| Benchmark | Claude Sonnet 5.5 | GPT-5.1-Codex |
|---|---|---|
| GPQA Diamond | 95.6% | — |
| SimpleQA Verified | 46.5% | — |
| LMArena Expert | 1540 | — |
Multimodal Not comparable
Claude Sonnet 5.5: 51.5 (#6), GPT-5.1-Codex: —
| Benchmark | Claude Sonnet 5.5 | GPT-5.1-Codex |
|---|---|---|
| LMArena Vision | 1289 | — |
| Furniture Assembly | 75% | — |
Multilingual Not comparable
Claude Sonnet 5.5: 55.3 (#30), GPT-5.1-Codex: —
| Benchmark | Claude Sonnet 5.5 | GPT-5.1-Codex |
|---|---|---|
| LMArena Non-English | 1452 | — |
| LMArena Chinese | 1522 | — |
| LMArena Russian | 1451 | — |
Instruction Following Not comparable
Claude Sonnet 5.5: 78.3 (#11), GPT-5.1-Codex: —
| Benchmark | Claude Sonnet 5.5 | GPT-5.1-Codex |
|---|---|---|
| LMArena Instruction Following | 1495 | — |
Long Context Not comparable
Claude Sonnet 5.5: 45.9 (#28), GPT-5.1-Codex: —
| Benchmark | Claude Sonnet 5.5 | GPT-5.1-Codex |
|---|---|---|
| LMArena Longer Query | 1498 | — |
Writing & Preference Not comparable
Claude Sonnet 5.5: 66.0 (#40), GPT-5.1-Codex: —
| Benchmark | Claude Sonnet 5.5 | GPT-5.1-Codex |
|---|---|---|
| LMArena Text | 1471 | — |
| LMArena Creative Writing | 1465 | — |
| LMArena Multi-Turn | 1474 | — |
Frequently asked questions
Is Claude Sonnet 5.5 better than GPT-5.1-Codex?
Claude Sonnet 5.5 is the stronger model overall, scoring 61.9 to 38.6 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: 67.3 versus 41.9 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 32 scored results on Noometry and GPT-5.1-Codex has 6.