We've been talking about this problem for three years and there's not been much progress in finding a robust solution.

Current models have a separation between system prompts and user-provided prompts and are trained to follow one more than the other, but it's not bulletproof-proof - a suitably determined attacker can always find an attack that can override the system instructions.

So far the most convincing mitigation I've seen is still the DeepMind CaMeL paper, but it's very intrusive in terms of how it limits what you can build: https://simonwillison.net/2025/Apr/11/camel/