> "...included a $72 billion accounting charge reflecting an increase in the estimated value of bonds that could eventually convert into Anthropic shares,"
I think all this means is that Anthropic's valuation went up. Anthropic owes holders of convertible debt[0] a fixed number of their post-IPO shares. Since Anthropic's valuation rose, the book value of the shares they owe to these note-holders went up.
On paper, this is a "loss", because the valuation of their debt increased when they recomputed it. In practice, these notes function like equity.
This is a positive signal that looks bad because the accounting is counterintuitive.