Junk ratings are not investment grade. They’re rating this debt as at least a little bit sketchy.

From the article:

"The rating action, which has not previously been reported, shows Anthropic is close to achieving the investment-grade status that would allow the start-up to lower its borrowing costs and tap a wider pool of institutional investors including life insurance companies and pension funds.

Bankers for Anthropic and rival OpenAI have lobbied the largest rating agencies to grant the AI labs investment-grade ratings once they go public."