Anthropic is working on a deal to let some employees sell shares in the company at a valuation of at least $350 billion, according to a person familiar with the matter, a plan that is coming together at the same time as a funding round that could bring in more than $20 billion.The tender offer would allow Anthropic staffers to cash out some equity in one of the world’s most richly valued artificial intelligence startups. The $350 billion valuation is the same one being discussed in the company’s...