GPT-5.3 Codex
ECI#15
157GPT-5.3 Codex is a closed-weights model from OpenAI, released February 5, 2026. It has an ECI score of 157 and ranks 15th of 249 tracked models. At the time of its release, it ranked 1st of 181 tracked models.
GPT-5.3 Codex vs select alternatives
| Domain | Benchmark | GPT-5.3 Codex | |||
|---|---|---|---|---|---|
ECI scoreBest score 166 | 157 | 155 | 155 | 153 | |
| Ranking | #15 | #23 | #24 | #35 | |
| Agent | Vending-Bench 2Best score $11,182 | $5,940 | — | $8,018 | $5,478 |
APEX-AgentsBest score 47% | |||||
| Software engineering | METR Time HorizonsBest score 17 hr 25 min | 5 hr 50 min | — | 11 hr 59 min | 3 hr 44 min |
Text Arena (Coding)Best score 1797 | 1369 | — | 1556 | 1438 | |
ALE-BenchBest score 2177 | 1655 | — | 997 | 1177 | |
SWE-bench VerifiedBest score 83% | |||||
Terminal-Bench 2.0Best score 85% | |||||
WeirdML (v2)Best score 93% |
