Compare / head-to-head
Claude Sonnet 5.5vs
GPT-5.1-Codex
Claude Sonnet 5.5 leads 1 of 1 shared benchmark. GPT-5.1-Codex is 1.1x cheaper per token. Claude Sonnet 5.5 has the larger context window (1M tokens).
Benchmarks from cited public sources; pricing from official pages; status from official provider feeds.
Shared benchmarks
1 – 0
Claude Sonnet 5.5 leads
Cheaper per token
GPT-5.1-Codex
1.1x cheaper, input + output
Larger context
Claude Sonnet 5.5
1M tokens
Providers
2 providers
Anthropic · OpenAI
Claude Sonnet 5.5
Anthropic · released 2026-09-28
textvision
GPT-5.1-Codex
OpenAI · released 2025-11-13
textvision
Quality
Benchmark matrix
1 shared · 28 only Claude Sonnet 5.5 · 3 only GPT-5.1-Codex| Benchmark | Claude Sonnet 5.5 | GPT-5.1-Codex | Δ | Edge |
|---|---|---|---|---|
| Reported by both · 1 | ||||
| LMArena WebDev (LMArena) | 1786.3 ↗ | 1337.1 ↗ | +449.2 | Claude Sonnet 5.5 |
| Only Claude Sonnet 5.5 reports · 28 | ||||
| GPQA Diamond | 95.6% ↗epoch run | not reported | — | — |
| LMArena Elo | 1471 ↗ | not reported | — | — |
| APEX-Agents (Mercor) | 75.5% ↗ | not reported | — | — |
| Chartography (no tools) | 61.6% ↗ | not reported | — | — |
| CursorBench 4.0 | 55.5% ↗ | not reported | — | — |
| FrontierCode v1.1 (Main) | 46.2% ↗ | not reported | — | — |
| FrontierMath Tier 4 v2 (Epoch AI run) | 80.5% ↗epoch run | not reported | — | — |
| FrontierMath Tiers 1-3 v2 (Epoch AI run) | 88.8% ↗epoch run | not reported | — | — |
| FrontierSWE V2 (Proximal Labs) | 61.9% ↗ | not reported | — | — |
| Furniture Assembly (Epoch AI run) | 75% ↗epoch run | not reported | — | — |
| Humanity's Last Exam (with tools) | 64.5% ↗ | not reported | — | — |
| LiveBench Agentic Coding (LiveBench) | 56.3% ↗ | not reported | — | — |
| LiveBench Coding (LiveBench) | 91.4% ↗ | not reported | — | — |
| LiveBench Data Analysis (LiveBench) | 78.6% ↗ | not reported | — | — |
| LiveBench Instruction Following (LiveBench) | 70.5% ↗ | not reported | — | — |
| LiveBench Language (LiveBench) | 83.4% ↗ | not reported | — | — |
| LiveBench Mathematics (LiveBench) | 96.7% ↗ | not reported | — | — |
| LiveBench Reasoning (LiveBench) | 91.6% ↗ | not reported | — | — |
| LMArena Agent (LMArena) | 0.1252 ↗ | not reported | — | — |
| LMArena Vision (LMArena) | 1268.3 ↗ | not reported | — | — |
| Mystery Game Puzzles (Epoch AI run) | 65% ↗epoch run | not reported | — | — |
| OSWorld 2.1 (partial) | 80.1% ↗ | not reported | — | — |
| OTIS Mock AIME 2024-2025 (Epoch AI run) | 100% ↗epoch run | not reported | — | — |
| SAGE (Vals AI) | 51.8% ↗ | not reported | — | — |
| SimpleBench (SimpleBench) | 75.9% ↗ | not reported | — | — |
| SimpleQA Verified | 46.5% ↗epoch run | not reported | — | — |
| Terminal-Bench 4.0 | 70.6% ↗ | not reported | — | — |
| Terminal-Bench 4.0 (Vals AI) | 64.1% ↗ | not reported | — | — |
| Only GPT-5.1-Codex reports · 3 | ||||
| SWE-bench Verified | not reported | 73.7% ↗ | — | — |
| SWE-Lancer IC SWE | not reported | 66.3% ↗ | — | — |
| Terminal-Bench 2.0 | not reported | 52.8% ↗ | — | — |
Scores tagged "epoch" or "matharena" are independent runs, used only where the lab has not published its own; ⚠ marks rows MathArena flags as released after the competition. Higher is better on every row. Δ is Claude Sonnet 5.5 minus GPT-5.1-Codex in the benchmark's own unit. "Not reported" means the lab has not published that figure; it is not a zero. ↗ opens the source.
Specs & pricing
Side by side
Official pricing pages and model cards| Spec | Claude Sonnet 5.5 | GPT-5.1-Codex | Edge |
|---|---|---|---|
| Context window | 1M tokens | 400K tokens | Claude Sonnet 5.5 |
| Max output | 128K tokens | 128K tokens | Tie |
| Input price / 1M | $2 ↗ | $1.25 ↗ | GPT-5.1-Codex |
| Output price / 1M | $10 ↗ | $10 ↗ | Tie |
| Cached input / 1M | $0.2 ↗ | $0.125 ↗ | GPT-5.1-Codex |
| Input + output / 1M Lower is cheaper. List prices; batch, tool and regional fees excluded. | $12 | $11.25 | GPT-5.1-Codex |
| Modalities | text · vision | text · vision | Tie |
| Released | 2026-09-28 | 2025-11-13 | — |
| Cited benchmark scores | 29 | 4 | — |
Reliability
Provider status
Live from /statusMore matchups
Claude Sonnet 5.5 vs …
Models sharing the most benchmarksMore matchups
GPT-5.1-Codex vs …
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Which one wins on your data?
Public benchmarks are a starting point. Run Claude Sonnet 5.5 and GPT-5.1-Codex on your own prompts with Respan evals, or route to either through one gateway key with automatic failover.