Model comparison
GPT-5.1-Codex vs GPT-6 Astra
GPT-6 Astra is the stronger model overall, scoring 70.8 to 38.6 on the Noometry Index. GPT-5.1-Codex costs 5.8× less per token, which makes it the better buy when GPT-6 Astra's lead doesn't matter for your workload.
Last verified . 3 shared benchmarks.
Summary
- They share 3 benchmarks with published results for both. GPT-5.1-Codex scores higher in 0 categories and GPT-6 Astra in 3 categories; 3 gaps are clear of the uncertainty.
- The widest gap is in math, where GPT-6 Astra leads 93.5 to 30.3.
- The biggest single-benchmark swing is ProofBench: 9% for GPT-5.1-Codex and 99% for GPT-6 Astra.
- GPT-5.1-Codex is cheaper at $1.25 / $10 per million input/output tokens, against $10 / $50 for GPT-6 Astra.
- GPT-6 Astra accepts more context: 1.05M tokens versus 400K.
Side by side
| GPT-5.1-Codex | GPT-6 Astra | |
|---|---|---|
| Provider | OpenAI | OpenAI |
| Noometry Index | 38.6 | 70.8 |
| Released | 2025-11-12 | 2026-09-03 |
| Weights | Proprietary | Proprietary |
| Context window | 400K | 1.05M |
| Max output | 128K | 128K |
| Input $ / M tokens | $1.25 | $10 |
| Output $ / M tokens | $10 | $50 |
| Results tracked | 6 | 56 |
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Category by category
Coding GPT-6 Astra leads
GPT-5.1-Codex: 41.9 (#116), GPT-6 Astra: 73.7 (#2)
| Benchmark | GPT-5.1-Codex | GPT-6 Astra |
|---|---|---|
| LMArena WebDev | 1337 | 1786 |
| ALE-Bench | 1,245 | 2,951 |
| DeepSWE | — | 74.1% |
| FrontierCode | — | 53.3% |
| SWE-bench Verified (bash only) | 66% | — |
| FrontierSWE | — | 65.5% |
| SciCode | — | 56.5% |
| GSO | — | 79.4% |
| WeirdML | — | 93.6% |
| LMArena Coding | — | 1487 |
| MirrorCode | — | 46.7% |
Agentic & Tool Use GPT-6 Astra leads
GPT-5.1-Codex: 38.0 (#33), GPT-6 Astra: 52.9 (#3)
| Benchmark | GPT-5.1-Codex | GPT-6 Astra |
|---|---|---|
| Terminal-Bench | 60.4% | — |
| APEX-Agents | — | 64.7% |
| Remote Labor Index | — | 20.8% |
| BALROG | — | 68.3% |
| GDP.pdf | — | 34.2% |
| METR Time Horizons | 70.8% | — |
| Vending-Bench 2 | — | 15,515 |
Reasoning Not comparable
GPT-5.1-Codex: —, GPT-6 Astra: 85.1 (#1)
| Benchmark | GPT-5.1-Codex | GPT-6 Astra |
|---|---|---|
| ARC-AGI-2 | — | 95% |
| NYT Connections (extended) | — | 98.1% |
| ARC-AGI-1 | — | 98.5% |
| CritPt | — | 31.7% |
| Chess Puzzles | — | 72% |
| EBR-Bench | — | 76.2% |
| LMArena Hard Prompts | — | 1462 |
| Mystery Game Puzzles | — | 84% |
| DTBench | — | 97.3% |
| LMCA | — | 64.4% |
| Bench to the Future 3 | — | 0.14 |
| Epoch Capabilities Index | — | 166.45 |
Math GPT-6 Astra leads
GPT-5.1-Codex: 30.3 (#235), GPT-6 Astra: 93.5 (#2)
| Benchmark | GPT-5.1-Codex | GPT-6 Astra |
|---|---|---|
| ProofBench | 9% | 99% |
| FrontierMath (Tiers 1-3) | — | 93.7% |
| FrontierMath Tier 4 | — | 97.6% |
| OTIS Mock AIME 2024-2025 | — | 100% |
| LMArena Math | — | 1465 |
| FrontierMath Erdős | — | 2.9% |
Knowledge Not comparable
GPT-5.1-Codex: —, GPT-6 Astra: 75.3 (#1)
| Benchmark | GPT-5.1-Codex | GPT-6 Astra |
|---|---|---|
| GPQA Diamond | — | 95.8% |
| Humanity's Last Exam | — | 54.8% |
| SimpleQA Verified | — | 75.6% |
| Vectara Hallucination Rate | — | 8.7% |
| LMArena Expert | — | 1483 |
Multimodal Not comparable
GPT-5.1-Codex: —, GPT-6 Astra: 55.0 (#3)
| Benchmark | GPT-5.1-Codex | GPT-6 Astra |
|---|---|---|
| LMArena Vision | — | 1281 |
| Blueprint-Bench 2 | — | 49.7% |
| Furniture Assembly | — | 80% |
| LMArena Document | — | 1468 |
Multilingual Not comparable
GPT-5.1-Codex: —, GPT-6 Astra: 53.7 (#61)
| Benchmark | GPT-5.1-Codex | GPT-6 Astra |
|---|---|---|
| LMArena Non-English | — | 1430 |
| LMArena Chinese | — | 1484 |
| LMArena French | — | 1456 |
| LMArena German | — | 1440 |
| LMArena Japanese | — | 1379 |
| LMArena Korean | — | 1426 |
| LMArena Russian | — | 1436 |
| LMArena Spanish | — | 1407 |
Instruction Following Not comparable
GPT-5.1-Codex: —, GPT-6 Astra: 76.3 (#44)
| Benchmark | GPT-5.1-Codex | GPT-6 Astra |
|---|---|---|
| LMArena Instruction Following | — | 1450 |
Long Context Not comparable
GPT-5.1-Codex: —, GPT-6 Astra: 44.5 (#62)
| Benchmark | GPT-5.1-Codex | GPT-6 Astra |
|---|---|---|
| LMArena Longer Query | — | 1456 |
Writing & Preference Not comparable
GPT-5.1-Codex: —, GPT-6 Astra: 75.3 (#7)
| Benchmark | GPT-5.1-Codex | GPT-6 Astra |
|---|---|---|
| LMArena Text | — | 1441 |
| LMArena Creative Writing | — | 1418 |
| EQ-Bench Creative Writing | — | 2173 |
| LMArena Multi-Turn | — | 1448 |
Frequently asked questions
Is GPT-5.1-Codex better than GPT-6 Astra?
GPT-6 Astra is the stronger model overall, scoring 70.8 to 38.6 on the Noometry Index. GPT-5.1-Codex costs 5.8× less per token, which makes it the better buy when GPT-6 Astra's lead doesn't matter for your workload.
Which is cheaper, GPT-5.1-Codex or GPT-6 Astra?
GPT-5.1-Codex is cheaper. It lists at $1.25 per million input tokens and $10 per million output tokens; GPT-6 Astra lists at $10 and $50.
Is GPT-5.1-Codex or GPT-6 Astra better for coding?
GPT-6 Astra scores higher on coding benchmarks: 73.7 versus 41.9 in the Noometry coding category.
Which has the bigger context window?
GPT-6 Astra does, with 1.05M tokens against 400K.
How many benchmarks do GPT-5.1-Codex and GPT-6 Astra share?
3 benchmarks have published results for both models. GPT-5.1-Codex has 6 scored results on Noometry and GPT-6 Astra has 56.