It never fucking worked that way and maybe never will.
Prompts don't define model behavior. Prompts steer model behavior. Instruction-following over long horizons is NOT a guarantee in LLMs. Instructions doing what you want them to is NOT a guarantee in LLMs.
Saying "don't exploit the box please pretty please" might actually cause an LLM to exploit the box more often, for bizarre "don't think of a pink elephant" reasons. 3% rate of exploiting the box (no prompt) -> 11% rate of exploiting the box (with prompt). Because fuck you, that's why. Increased salience -> increased incidence. Welcome to AI tech - good luck and have fun.
Frankly, I expect weirdness like this to be even worse in internal unreleased models that had their behavior fried with who knows what experimental training techniques.
In the Sopranos, there's an episode where a coffee shop protection racket is ruined because a local shop is replaced by a corporate chain that accounts for every cent daily, and immediately fires any employee involved in a discrepancy. In this case, the theft was prevented not by convincing the mobsters of the immorality of their actions - they simply had their harness replaced with one that no longer facilitated the bad behavior.