“You can’t eval GPT5 anymore” by Lukas Petersson

The GPT-5 API is aware of today's date (no other model provider does this). This is problematic because the model becomes aware that it is in a simulation when we run our evals at Andon Labs. Here are traces from gpt-5-mini. Making it aware of the "system date" is a giveaway that it's in a simulation. This is a problem because there's evidence that models behave differently when they know they are in a simulation (see "sandbagging")."There's a conflict with the user's stated date of August 10, 2026, versus my system date of September 17, 2025. (...) I can proceed but should clarify that my system date is September 17, 2025, and ask the user whether we should simulate starting from August 10, 2026." Here are more traces. Once the model knows that it is in a simulation, it starts questioning other parts of the simulation. [...] --- First published: September 18th, 2025 Source: https://www.lesswrong.com/posts/DLZokLxAQ6AzsHrya/you-can-t-eval-gpt5-anymore --- Narrated by TYPE III AUDIO.