Word in town is [1] openai "plans" to let employees sell "some" equity through a "tender process" which ex-employees are excluded from; and also that openai can "claw back" vested equity, and has used the threat of doing so in the past to pressure people into signing sketchy legal documents.
I would definitely discount OpenAI equity compared to even other private AI labs (i.e. Anthropic) given the shenanigans, but they have in fact held 3 tender offers and former employees were not, as far as we know, excluded (though they may have been limited to selling $2m worth of equity, rather than $10m).
[1] https://www.cnbc.com/2024/06/11/openai-insider-stock-sales-a...