Maybe the agreement is "we will accelerate vesting of your unvested equity if you sign this new agreement"? If that's the case then it doesn't sound nearly so coercive to me.
all this said, in bigger picture I can understand not divulging trade secrets but not being allowed to discuss company culture towards AI safety essentially tells me that all the Sama talk about the 'for the good of humanity' is total BS. at the end of day its about market share and bottom line.