Anthropic says an unreleased research Claude raised the proven lower bound on nontrivial Riemann zeta zeros on the critical line from 41.6% to 67.2%. Working in Claude Code across two sessions, about 31 million output tokens, and roughly 60 subagents, it found the result after a staff prompt to attempt the Riemann hypothesis. Anthropic mathematicians checked the argument, experts Brian Conrey and Dan Goldston examined it, and Claude produced a Lean formalization. Why it matters: a frontier model moved a real analytic number theory constant, not a contest puzzle. Caveat: this is not a Riemann hypothesis proof, and journal peer review is still ahead.