Sure, there will always be some trust and interpretation involved. I'm sure whatever they spend it on will never satisfy everyone. But I'd rather criticize actual dishonesty and theft, not the specter of its potential. If they spend the money on cars for execs, I assume they'd open themselves up to lawsuits, hurt their image, and damage employee morale. Voting for an exec comp increase would be far less risky than fraud. I feel confident this announcement is genuine, but of course none of us can read minds.
You can see from their own past actions and all of human history that this is a ploy to launder their image. If you can't, then you are willfully ignorant. No company is ever going to do anything for the public good. Profit is the only motive for a capitalist.
Your theory is that this is self-interested PR. How does your theory explain why Anthropic is doing this, but so many other companies aren’t? If all company actions were self-interested, then wouldn’t you expect this to be a common move? Explaining why this is so uncommon requires either uncommon motive or uncommon circumstance. The theory that I find more explanatory is that the founders feel some degree of altruism and wish to exert their control over their company to effect their desired change in the world, especially before they go public and face greater scrutiny.