Model comparison
GPT-5.1-Codex vs GPT-5.5 Instant
GPT-5.5 Instant is the stronger model overall, scoring 42.7 to 38.6 on the Noometry Index.
Last verified . 0 shared benchmarks.
Summary
- The widest gap is in math, where GPT-5.1-Codex leads 30.3 to 26.5.
Side by side
| GPT-5.1-Codex | GPT-5.5 Instant | |
|---|---|---|
| Provider | OpenAI | OpenAI |
| Noometry Index | 38.6 | 42.7 |
| Released | 2025-11-12 | 2026-05-05 |
| Weights | Proprietary | Proprietary |
| Context window | 400K | — |
| Max output | 128K | — |
| Input $ / M tokens | $1.25 | — |
| Output $ / M tokens | $10 | — |
| Results tracked | 6 | 27 |
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Category by category
Coding GPT-5.5 Instant leads
GPT-5.1-Codex: 41.9 (#116), GPT-5.5 Instant: 44.3 (#74)
| Benchmark | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| SWE-bench Verified (bash only) | 66% | — |
| LMArena WebDev | 1337 | — |
| SciCode | — | 48.6% |
| LMArena Coding | — | 1433 |
| ALE-Bench | 1,245 | — |
Agentic & Tool Use Not comparable
GPT-5.1-Codex: 38.0 (#33), GPT-5.5 Instant: —
| Benchmark | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| Terminal-Bench | 60.4% | — |
| METR Time Horizons | 70.8% | — |
Reasoning Not comparable
GPT-5.1-Codex: —, GPT-5.5 Instant: 24.9 (#155)
| Benchmark | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| CritPt | — | 0% |
| Chess Puzzles | — | 12% |
| LMArena Hard Prompts | — | 1426 |
| Epoch Capabilities Index | — | 142.52 |
Math GPT-5.1-Codex leads
GPT-5.1-Codex: 30.3 (#235), GPT-5.5 Instant: 26.5 (#259)
| Benchmark | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| FrontierMath (Tiers 1-3) | — | 26.3% |
| FrontierMath Tier 4 | — | 2.4% |
| OTIS Mock AIME 2024-2025 | — | 68.1% |
| ProofBench | 9% | — |
| LMArena Math | — | 1420 |
Knowledge Not comparable
GPT-5.1-Codex: —, GPT-5.5 Instant: 48.9 (#74)
| Benchmark | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| GPQA Diamond | — | 82.5% |
| LMArena Expert | — | 1409 |
Multimodal Not comparable
GPT-5.1-Codex: —, GPT-5.5 Instant: 40.0 (#52)
| Benchmark | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Vision | — | 1250 |
| LMArena Document | — | 1403 |
Multilingual Not comparable
GPT-5.1-Codex: —, GPT-5.5 Instant: 52.8 (#80)
| Benchmark | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Non-English | — | 1417 |
| LMArena Chinese | — | 1456 |
| LMArena French | — | 1428 |
| LMArena German | — | 1411 |
| LMArena Japanese | — | 1408 |
| LMArena Korean | — | 1392 |
| LMArena Russian | — | 1431 |
| LMArena Spanish | — | 1429 |
Instruction Following Not comparable
GPT-5.1-Codex: —, GPT-5.5 Instant: 74.2 (#100)
| Benchmark | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Instruction Following | — | 1406 |
Long Context Not comparable
GPT-5.1-Codex: —, GPT-5.5 Instant: 43.4 (#96)
| Benchmark | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Longer Query | — | 1422 |
Writing & Preference Not comparable
GPT-5.1-Codex: —, GPT-5.5 Instant: 61.8 (#85)
| Benchmark | GPT-5.1-Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Text | — | 1419 |
| LMArena Creative Writing | — | 1419 |
| LMArena Multi-Turn | — | 1433 |
Frequently asked questions
Is GPT-5.1-Codex better than GPT-5.5 Instant?
GPT-5.5 Instant is the stronger model overall, scoring 42.7 to 38.6 on the Noometry Index.
Is GPT-5.1-Codex or GPT-5.5 Instant better for coding?
GPT-5.5 Instant scores higher on coding benchmarks: 44.3 versus 41.9 in the Noometry coding category.
How many benchmarks do GPT-5.1-Codex and GPT-5.5 Instant share?
0 benchmarks have published results for both models. GPT-5.1-Codex has 6 scored results on Noometry and GPT-5.5 Instant has 27.