Anthropic released Claude Fable 5.1 and Claude Mythos 5.1 on September 1, 2026, positioning the update as a new standard for coding, knowledge work and long-running problem solving. The model is generally available through the Claude API, Amazon Web Services, Google Cloud and Microsoft Azure under the identifier claude-fable-5-1.
Same model, two doors
Fable 5.1 and Mythos 5.1 are the same underlying model. Fable 5.1 is the general-availability version with Anthropic's production safeguards in place, while Mythos 5.1 is offered through restricted-access programs for vetted cybersecurity and life-sciences organizations. Anthropic says the safeguards were tuned so that Claude Code users should see roughly 60 percent fewer cybersecurity false positives, a common complaint from developers doing legitimate security work.
Pricing is the most practical change. Fable 5.1 keeps Fable 5's headline rates of $10 per million input tokens and $50 per million output tokens, but the cache-read rate drops 75 percent to $0.25 per million tokens. For agentic workloads that repeatedly re-read the same long context, that discount can matter more than the sticker price.
Anthropic also said text from Fable 5.1 and Mythos 5.1 carries its text watermark, and images and video produced through the code execution tool carry C2PA Content Credentials.
Claudeforce
The release landed a week after Salesforce and Anthropic announced Claudeforce on August 26, an expanded partnership that runs in both directions:
- Salesforce in Claude, a plugin with 37 prebuilt sales skills such as meeting prep, deal health review and pipeline review, available to select pilot customers now and expected in open beta this month.
- Claude in Salesforce, where Claude powers the Atlas Reasoning Engine inside Agentforce, delivered through Amazon Bedrock within the Salesforce trust boundary.
- Claude as the default model for Slack, powering Slackbot, Claude Tag and Slack Code.
Salesforce said its internal use of Slackbot has produced 8.1 million hours of annualized productivity gains, more than doubling quarter over quarter. Anthropic CEO Dario Amodei described the deal as bringing frontier intelligence into the systems where much of the world's commercial activity already happens.
Source: VentureBeat, Salesforce
Photo: VentureBeat (source)
