Model comparison
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.
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 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.
Side by side
| Claude Sonnet 5.5 | GPT-5.1-Codex | |
|---|---|---|
| Provider | Anthropic | OpenAI |
| Noometry Index | 60.5 | 38.2 |
| 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 | 16 | 6 |
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Category by category
Coding Claude Sonnet 5.5 leads
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 leads
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 Not comparable
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 leads
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 Not comparable
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 Not comparable
Claude Sonnet 5.5: 53.2 (#5), GPT-5.1-Codex: —
| Benchmark | Claude Sonnet 5.5 | GPT-5.1-Codex |
|---|---|---|
| Furniture Assembly | 75% | — |
Frequently asked questions
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.