“Anthropic withheld Claude Mythos Preview in April 2026 for having too high a blast radius and reports that model-layer defenses are strong but imperfect—Claude Opus 4.7 holds prompt-injection attack success to about 0.1% on single attempts and roughly 5–6% after 100 adaptive attempts—so overlapping defenses across environment, model, and external content are required.”

#2 📝 Anthropic Engineering How we contain Claude across products - Anthropic deploys three agentic products—claude.ai, Claude Code, and Claude Cowork—using two containment strategies: human-in-the-loop approvals (users approved roughly 93% of permission prompts) and environmental containment (sandboxes, VMs, filesystem and egress controls); Claude Code’s auto mode automates safer approvals and catches roughly 83% of overeager behaviors before they execute. Anthropic withheld Claude Mythos Preview in April 2026 for having too high a blast radius and reports that model-layer defenses are strong but imperfect—Claude Opus 4.7 holds prompt-injection attack success to about 0.1% on single attempts and roughly 5–6% after 100 adaptive attempts—so overlapping defenses across environment, model, and external content are required.

“Layered defenses—environmental sandboxes/VMs/egress controls, model-layer system prompts/classifiers/training, and limiting external content—are used across claude.ai, Claude Code, and Cowork; telemetry shows users approved roughly 93% of permission prompts, Claude Code auto mode blocks about 83% of overeager behaviors before execution, Claude Opus 4.7 holds prompt-injection success to ~0.1% on single attempts (~5–6% after 100 adaptive attempts), and Claude Mythos Preview was judged too high-risk to ship in April 2026.”

The preview model appears in the context of Anthropic's product safety decisions. It was not shipped because of perceived risk.

“Anthropic has deployed Claude across claude.ai, Claude Code, and Claude Cowork while containing blast radius via environment controls (sandboxes, VMs, filesystem/egress limits), model-layer controls (system prompts, classifiers, probes, training), and restricting external-content/tool access, noting Claude Mythos Preview was judged too risky to ship in April 2026.”

📝 Anthropic Engineering How we contain Claude across products - Anthropic has deployed Claude across claude.ai, Claude Code, and Claude Cowork while containing blast radius via environment controls (sandboxes, VMs, filesystem/egress limits), model-layer controls (system prompts, classifiers, probes, training), and restricting external-content/tool access, noting Claude Mythos Preview was judged too risky to ship in April 2026. Telemetry showed users approved ~93% of permission prompts, Claude Code auto mode blocks roughly 83% of overeager behaviors before execution, and Claude Opus 4.7 resists prompt-injection with about 0.1% success on single attempts and ~5–6% after 100 adaptive attempts.

“𝕏 Anthropic expands Project Glasswing, rolling out Claude Mythos Preview to roughly 150 more organizations across 15+ countries.”

#3 𝕏 Anthropic expands Project Glasswing, rolling out Claude Mythos Preview to roughly 150 more organizations across 15+ countries.

“Also, Opus 4.8 is about four times less likely than Opus 4.7 to let code flaws pass unremarked, scored 84% on Online-Mind2Web, was the only model to complete every Super-Agent case end-to-end (beating prior Opus models and GPT-5.5), is the first to break 10% on the Legal Agent all-pass standard, and shows misalignment rates similar to Claude Mythos Preview while Genie users report 61% cheaper token cost versus Opus 4.7 for multimodal reasoning.”

Anthropic releases Claude Opus 4.8 with dynamic workflows #1 📝 Anthropic News Introducing Claude Opus 4.8 - Anthropic released Claude Opus 4.8 today at the same price as Opus 4.7, adding user-selectable effort levels, Claude Code “dynamic workflows,” and a fast mode that runs 2.5× faster and is three times cheaper than on prior models. The company reports broad capability and alignment gains—Opus 4.8 is about four times less likely than Opus 4.7 to let code flaws pass unremarked, scored 84% on Online-Mind2Web, was the only model to complete every Super-Agent case end-to-end (beating prior Opus models and GPT-5.5), is the first to break 10% on the Legal Agent all-pass standard, and shows misalignment rates similar to Claude Mythos Preview while Genie users report 61% cheaper token cost versus Opus 4.7 for multimodal reasoning. Also covered by: @v0 , @There's An AI For That , @There's An AI For That , @Aravind Srinivas , @claire vo 🖤, building @chatprd , @Mike Krieger , @Claude, @Cognition, @Claire Vo , @Dan Shipper , @How I AI Podcast

“Project Glasswing: An initial update - Project Glasswing, launched last month, used Claude Mythos Preview with about 50 partners to surface more than 10,000 high- or critical‑severity vulnerabilities in systemically important software (Cloudflare reported 2,000 bugs, 400 high/critical) and partners say bug‑finding rates increased by over tenfold.”

Anthropic launches Project Glasswing security scanner #1 📝 Anthropic News Project Glasswing: An initial update - Project Glasswing, launched last month, used Claude Mythos Preview with about 50 partners to surface more than 10,000 high- or critical‑severity vulnerabilities in systemically important software (Cloudflare reported 2,000 bugs, 400 high/critical) and partners say bug‑finding rates increased by over tenfold. Anthropic also scanned over 1,000 open‑source projects and estimated 6,202 high/critical issues out of 23,019 total, triaged 1,752 of those (90.6% true positives, 62.4% confirmed high/critical), found concrete exploits including wolfSSL's CVE-2026-5194, and says the new bottleneck is human triage, disclosure, and patching. Also covered by: @Mario Zechner #2 𝕏 Anthropic reports that Claude Mythos Preview uncovers a surge of security vulnerabilities, meaning patching them boosts safety but forces the software industry to scale its processes—as detailed in their initial Project Glasswing update.

“#10 📝 Simon Willison Bobby Holley - A quoted excerpt from Bobby Holley (CTO, Firefox) describing how Anthropic's Claude Mythos Preview helped identify many vulnerabilities in Firefox and expressing optimism that defenders can now decisively win by focusing on security work.”

#10 📝 Simon Willison Bobby Holley - A quoted excerpt from Bobby Holley (CTO, Firefox) describing how Anthropic's Claude Mythos Preview helped identify many vulnerabilities in Firefox and expressing optimism that defenders can now decisively win by focusing on security work.

“DeepLearning.AI highlights Anthropic’s Claude Mythos Preview, an AI model that autonomously finds and exploits critical software vulnerabilities; it’s currently limited to industry partners to uncover and patch flaws before any public release.”

#3 𝕏 DeepLearning.AI highlights Anthropic’s Claude Mythos Preview, an AI model that autonomously finds and exploits critical software vulnerabilities; it’s currently limited to industry partners to uncover and patch flaws before any public release. #4 𝕏 OpenAI research lead Joy Jiao and product lead Yunyun Wang joined Andrew Mayne on the OpenAI Podcast to unveil the new Life Sciences model series for biology, drug discovery, and translational medicine.

“Anthropic published a detailed technical report on software vulnerabilities and exploits uncovered in Claude Mythos Preview, outlining the specific flaws, attack vectors, and mitigation strategies.”

#1 𝕏 Anthropic published a detailed technical report on software vulnerabilities and exploits uncovered in Claude Mythos Preview, outlining the specific flaws, attack vectors, and mitigation strategies. Also covered by: @Anthropic , @Boris Cherny , @Greg Isenberg , @Simon Willison