Model comparison
GPT-5.3 Codex vs GPT-5.5 Instant
GPT-5.3 Codex is the stronger model overall, scoring 45.5 to 42.5 on the Noometry Index.
Last verified . 1 shared benchmarks.
Summary
- They share 1 benchmark with published results for both. GPT-5.3 Codex scores higher in 1 category and GPT-5.5 Instant in 0 categories; one gap is clear of the uncertainty.
- The widest gap is in coding, where GPT-5.3 Codex leads 48.5 to 43.7.
Side by side
| GPT-5.3 Codex | GPT-5.5 Instant | |
|---|---|---|
| Provider | OpenAI | OpenAI |
| Noometry Index | 45.5 | 42.5 |
| Released | 2026-02-05 | 2026-05-05 |
| Weights | Proprietary | Proprietary |
| Context window | 400K | — |
| Max output | 128K | — |
| Input $ / M tokens | $1.75 | — |
| Output $ / M tokens | $14 | — |
| Results tracked | 8 | 27 |
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Category by category
Coding GPT-5.3 Codex leads
GPT-5.3 Codex: 48.5 (#51), GPT-5.5 Instant: 43.7 (#73)
| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| SWE-bench Verified | 74.8% | — |
| LMArena WebDev | 1408 | — |
| SciCode | — | 48.6% |
| WeirdML | 79.3% | — |
| LMArena Coding | — | 1433 |
| ALE-Bench | 1,655 | — |
Agentic & Tool Use Not comparable
GPT-5.3 Codex: 47.8 (#9), GPT-5.5 Instant: —
| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| Terminal-Bench | 78.4% | — |
| METR Time Horizons | 74.5% | — |
| Vending-Bench 2 | 5,940 | — |
Reasoning Not comparable
GPT-5.3 Codex: —, GPT-5.5 Instant: 24.2 (#149)
| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| Epoch Capabilities Index | 156.84 | 142.48 |
| CritPt | — | 0% |
| Chess Puzzles | — | 12% |
| LMArena Hard Prompts | — | 1426 |
Math Not comparable
GPT-5.3 Codex: —, GPT-5.5 Instant: 26.1 (#241)
| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| FrontierMath (Tiers 1-3) | — | 26.3% |
| FrontierMath Tier 4 | — | 2.4% |
| OTIS Mock AIME 2024-2025 | — | 68.1% |
| LMArena Math | — | 1420 |
Knowledge Not comparable
GPT-5.3 Codex: —, GPT-5.5 Instant: 48.9 (#68)
| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| GPQA Diamond | — | 82.5% |
| LMArena Expert | — | 1409 |
Multimodal Not comparable
GPT-5.3 Codex: —, GPT-5.5 Instant: 39.3 (#48)
| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Vision | — | 1250 |
| LMArena Document | — | 1403 |
Multilingual Not comparable
GPT-5.3 Codex: —, GPT-5.5 Instant: 53.0 (#76)
| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Non-English | — | 1417 |
| LMArena Chinese | — | 1457 |
| LMArena French | — | 1428 |
| LMArena German | — | 1410 |
| LMArena Japanese | — | 1408 |
| LMArena Korean | — | 1393 |
| LMArena Russian | — | 1430 |
| LMArena Spanish | — | 1430 |
Instruction Following Not comparable
GPT-5.3 Codex: —, GPT-5.5 Instant: 74.4 (#94)
| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Instruction Following | — | 1407 |
Long Context Not comparable
GPT-5.3 Codex: —, GPT-5.5 Instant: 43.4 (#92)
| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Longer Query | — | 1422 |
Writing & Preference Not comparable
GPT-5.3 Codex: —, GPT-5.5 Instant: 62.0 (#81)
| Benchmark | GPT-5.3 Codex | GPT-5.5 Instant |
|---|---|---|
| LMArena Text | — | 1419 |
| LMArena Creative Writing | — | 1420 |
| LMArena Multi-Turn | — | 1434 |
Frequently asked questions
Is GPT-5.3 Codex better than GPT-5.5 Instant?
GPT-5.3 Codex is the stronger model overall, scoring 45.5 to 42.5 on the Noometry Index.
Is GPT-5.3 Codex or GPT-5.5 Instant better for coding?
GPT-5.3 Codex scores higher on coding benchmarks: 48.5 versus 43.7 in the Noometry coding category.
How many benchmarks do GPT-5.3 Codex and GPT-5.5 Instant share?
1 benchmark has published results for both models. GPT-5.3 Codex has 8 scored results on Noometry and GPT-5.5 Instant has 27.