Latest
  1. Johns Hopkins Bayview tells 3,182 patients an employee put their health data into a public AI tool
  2. China’s AI compute access expected to double in 2027, with US-designed chips about 65 per cent
  3. UK commits £100m to national AI Biosecurity Lab
  4. Moonshot AI releases Kimi K3.1 Pro with 1-million-token context window
  5. Residents in Newport and Cardiff oppose hyperscale datacentres near homes
  6. Study: Grok 4.7 picked Republicans in 92% of forced midterm answers, GPT-6.1 Sol picked Democrats in 97%
  7. Attackers exploiting the PHP flaws hand the break-in to AI agents, Unit 42 says
  8. Elvis Presley’s rightsholders sue Anthropic over training on 274 songs

Latest / Frontier models and safety

Model releaseFrontierUSConfirmed

Anthropic releases Claude Fable 5.1 and Mythos 5.1 with cheaper cache reads

See how this story connects

Source: Anthropic: Introducing Claude Fable 5.1 and Claude Mythos 5.1Also reported by SD Times

Anthropic released Claude Fable 5.1 and Claude Mythos 5.1, the same model with different safeguards: Fable 5.1 is generally available and Mythos 5.1 is limited to trusted-access programmes for cybersecurity and life sciences. Cache reads fell 75% to $0.25 per million tokens, which Anthropic estimates cuts typical costs by about 25% against Fable 5. It said its new cyber safeguards produce 60% fewer false positives.

Why it matters

Agent-heavy users of Anthropic’s top model pay about 25% less on typical workloads, and fewer legitimate security requests get blocked.

When
2 Sep 2026
ID
WTA-N-2026-0182
Who
Anthropic

Summary by wheresthe.ai, from Anthropic and the reporting credited above. Checked against the source on 9 Oct 2026.

Read the original at Anthropic

Source copy: download the page as saved on 18 Oct 2026 (PDF). Also held by the Internet Archive.

Earlier in this Storyline: What led hereAnthropic launches Claude Fable 5 for general use and Mythos 5 for cyber defenders

Cite this story

WTA-N-2026-0182: “Anthropic releases Claude Fable 5.1 and Mythos 5.1 with cheaper cache reads.” wheresthe.ai, 2 Sep 2026. https://wheresthe.ai/d/anthropic-claude-fable-mythos-5-1-release-2026-09/ (source: Anthropic: Introducing Claude Fable 5.1 and Claude Mythos 5.1).

Spotted an error? Email [email protected].