GPT-4 launched and began its 52-week reign at the top of the ECI

GPT-5.5 fully solved TLO enterprise network simulation in 2 of 10 attempts

GPT-5.5 scored 71.4% on AISI expert CTF tasks, matching Claude Mythos Preview

Early user review of GPT-5.5 in Codex highlights major improvements

GPT-5.5 model family achieves leading position on Artificial Analysis Index for cost-performance

OpenAI engineer reveals GPT-5.5 is a Blackwell-native model trained on Nvidia GB200/GB300 NVL72 systems.

GPT-5.5 spotted via Codex API backdoor, suggesting unofficial release channel for image generation.

Release of GPT-4, which established OpenAI's early dominance in the AI race.

GPT-4 surpassed on ECI by GPT-4o and Claude 3.5 Sonnet, ending 18-month reign.

Official public launch of GPT-4 by OpenAI