It also occurs to me that the causality could go the other way: Ilya and Jan may have timed their departure to coincide with the 4o release for a number of reasons. If they go on to launch a new safety org soon, for example, I'd be more inclined to think that the timing of the two events was a result of Ilya/Jan trying to use the moment to their advantage.

Pure speculation: The timing of these departures being the day after the big, attention-grabbing GPT-4o release makes me think that there was a fixed date for Ilya and Jan to leave, and OpenAI lined up the release and PR to drown out coverage. Especially in light of Ilya not (apparently) being very involved with GPT-4o.