Anthropic Releases Two Versions of Claude Mythos 5, One Public and One Restricted to Cybersecurity Users

Anthropic released Claude Fable 5 on Tuesday, June 10, 2026, the first public model in its Mythos class. The company also released Claude Mythos 5, which is available only to vetted users in cybersecurity and critical infrastructure. The public version offers stronger reasoning and coding abilities while attempting to block dangerous uses.

8 in fewer than 5% of sessions. Specialized cybersecurity teams and more than 1,000 hours of external bug-bounty work found no universal way of breaking the safety system, the company said. Anthropic acknowledged that determined, well-funded attackers are expected to try to circumvent the measures.

DeFi protocols lost more than $840 million to hacks in the first five months of 2026, according to DefiLlama data. April 2026 accounted for more than $600 million in losses, the worst month on record for the sector. A North Korea-linked group drained about $285 million from Drift Protocol after a six-month social-engineering campaign.

An attacker exploited a single-verifier flaw to siphon roughly $292 million from Kelp DAO. Humanity Protocol lost over $30 million to a private-key compromise on Tuesday, June 10, 2026. CoinDesk reported that a hacker gained access to three out of six private keys on one employee’s laptop.

Charles Guillemet, chief technology officer at Ledger, stated: "Current AI guardrails raise friction. " Guillemet said the shift is less about AI inventing new kinds of hacks and more about how long it takes to create them. A reasoning model can "diff every commit, grep every config, and enumerate every misconfiguration at machine speed," he said.

Pendle has used Anthropic’s models defensively since the first version of Claude Opus. The team uses AI to map its codebase and stress-test its contracts, including freshly deployed ones. Pendle’s developers said in an interview over Telegram that smart contracts are short and have only about a dozen entry points.