According to this person, some problems are only "solved" by modern models: https://nitter.netbub.com/AlexKrentsel/status/21173766837246...

(opus <= 4.8 and gpt <= 5.5 couldn't match a PPO baseline network, and 5.6-sol and opus5 could barely match it. The 20x baseline improvement only comes from opus5.5 and sol > 6.1 / Astra)