# Claude Fable 5.1 ![Organization](https://img.shields.io/badge/Org-Anthropic-d97757) ![License](https://img.shields.io/badge/License-Proprietary-d29922) ![Modality](https://img.shields.io/badge/Modality-Text%20%2B%20Vision-8957e5) ![Released](https://img.shields.io/badge/Released-Sep%202026-555) > **Quick answer:** Claude Fable 5.1 is Anthropic's September 2026 update to the Fable line, generally available on all major clouds (AWS, Google Cloud, Microsoft Azure) via the API as `claude-fable-5-1`. It scores 52.6% on Terminal-Bench-Science 0.1, 55.8% on Terminal-Bench 4.0, a 1853 Elo on GDPval-AA v2, and 73.4% on CursorBench — sizeable gains over its predecessor, Fable 5, at roughly 25% lower typical cost (up to ~45% lower for highly agentic workloads) thanks to a 75%-cheaper cache-read price. ## Access Status Unlike Claude Fable 5 (suspended under a June 2026 US export control directive), Claude Fable 5.1 is generally available today across the Claude API, Amazon Bedrock, Google Cloud, and Microsoft Azure. Its higher-safeguard sibling, [Claude Mythos 5.1](/models/anthropic/claude-mythos-5-1), is restricted to Anthropic's Cyber Verification Program (CVP) and Life Sciences Verification Program (LSVP). ## At a Glance **Where Claude Fable 5.1 leads** - 55.8% Terminal-Bench 4.0 — up from Fable 5's 42.0% on the same suite - 52.6% Terminal-Bench-Science 0.1 — more than double Fable 5's reproduced 24.7% - 1853 Elo on GDPval-AA v2 — ahead of Claude Opus 5 (1824) and GPT-5.6 Sol (1711) - 73.4% CursorBench — new reported high, ahead of Grok 4.6's 69.9% - 31.4% AutomationBench, versus 17.1% for Fable 5 - ~25% lower cost than Fable 5 for typical workloads; up to ~45% lower for highly agentic, cache-heavy workloads **Where it lags** - Pricing unchanged from Fable 5 at the token-rate level: $10 / $50 per 1M input / output tokens (savings come from cheaper cache reads, not headline rates) - Cybersecurity and life-sciences dual-use tasks are still redirected to Opus-class models or require Mythos 5.1 trusted access - Evaluated with production safeguards enabled, which Anthropic notes can suppress scores on OSWorld 2.0 and AutomationBench when they intervene **Best for:** Coding agents, long-running agentic workflows, and knowledge-work tasks where both accuracy and per-task cost matter. ## What Claude Fable 5.1 Is Claude Fable 5.1 is Anthropic's incremental update to the Fable line, announced September 3, 2026 alongside [Claude Mythos 5.1](/models/anthropic/claude-mythos-5-1). Anthropic describes Fable 5.1 and Mythos 5.1 as the same underlying model shipped with different safeguard configurations — Fable 5.1 for general availability, Mythos 5.1 for vetted cyberdefense and life-sciences use through trusted access programs. Anthropic frames the release around three customer-feedback areas: price (an estimated 25% reduction for typical workloads, driven by a 75% cut to cache-read pricing to $0.25 per million tokens), data retention (new Enterprise Frontier Safeguards letting customers store data on their own cloud infrastructure), and safeguards precision (cybersecurity false positives cut by roughly 60%, with Fable 5.1 now permitted to identify — but not exploit — software vulnerabilities). On benchmarks, Fable 5.1 shows broad gains over Fable 5 across agentic scientific research, agentic coding, knowledge work, computer use, multidisciplinary reasoning, business-workflow automation, and in-IDE coding tasks, while running at default "High" effort in Claude Code and "Medium" effort in Claude Cowork and Claude.ai. ## Specifications | Field | Value | |---|---| | Organization | Anthropic | | Parameters | Undisclosed | | Context window | Undisclosed | | Architecture | Undisclosed (Fable line) | | License | Proprietary (API only) | | Modality | Text + Vision (multimodal) | | Knowledge cutoff | October 2025 (estimated) | | API name | `claude-fable-5-1` | | Access status | Generally available (Sept 2026) | ## Pricing Claude Fable 5.1's per-token pricing is unchanged from Fable 5: **$10 per 1M input tokens / $50 per 1M output tokens**. The cost reduction instead comes from cache reads, cut 75% to $0.25 per million tokens — Anthropic reports this yields ~25% lower cost for typical workloads and up to ~45% lower cost for highly agentic, context-heavy work where cache reads dominate spend. ## Benchmark Results | Category | Benchmark | Fable 5.1 | Fable 5 | Opus 5 | GPT-5.6 Sol | |---|---|---|---|---|---| | Agentic scientific research | [Terminal-Bench-Science 0.1](/benchmarks/anthropic/terminal-bench-science-0-1) | 52.6% | 24.7% | 29.0% | 22.4% | | Agentic coding | [Terminal-Bench 4.0](/benchmarks/anthropic/terminal-bench-4) | 55.8% | 42.0% | 52.3% | 37.3% | | Knowledge work | [GDPval-AA v2](/benchmarks/artificial-analysis/gdpval-aa-v2) | 1853 | 1723* | 1824* | 1711* | | Computer use | [OSWorld 2.0](/benchmarks/osworld/osworld-20) | 77.9% (partial) / 41.7% (strict) | 72.9% / 36.1% | 75.4% / 39.6% | — | | Multidisciplinary reasoning | [Humanity's Last Exam](/benchmarks/center-for-ai-safety-scale-ai/humanitys-last-exam) | 60.9% (no tools) / 65.0% (with tools) | 57.8% / 63.8% | 56.6% / 63.6% | — | | Business workflows | [AutomationBench](/benchmarks/zapier/automationbench) | 31.4% | 17.1% | 26.9% | 19.6% | | Agentic coding | [CursorBench](/benchmarks/cursor/cursorbench) | 73.4% | 70.5% | 70.0% | 67.2% | *Fable 5, Opus 5, and GPT-5.6 Sol figures on this specific comparison table are Anthropic's own reproduction for the Fable 5.1 launch and may differ slightly from previously published scores for those models on Benchgen due to methodology/harness differences (e.g. Fable 5's separately reported GDPval-AA v2 score of 1760). On Terminal-Bench 4.0, Anthropic also reports a **60.9%** score for Claude Mythos 5.1 (Fable 5.1's higher-safeguard, trusted-access-only sibling) — the strongest score across all evaluated models. *Scores reported by Anthropic, September 2026, evaluated with production safeguards enabled. Anthropic notes safeguard interventions can reduce Fable 5.1's/Fable 5's scores on OSWorld 2.0 and AutomationBench, since cybersecurity and biology tasks that trigger interventions are completed by Claude Opus models instead.* ## Frequently Asked Questions

What is Claude Fable 5.1?

Claude Fable 5.1 is Anthropic's September 2026 update to its Fable model line, generally available via the Claude API and major cloud partners, with gains across coding, scientific-research, and knowledge-work benchmarks over Fable 5.

How is Claude Fable 5.1 different from Claude Mythos 5.1?

Anthropic describes them as the same underlying model with different safeguard levels — Fable 5.1 is generally available, while Mythos 5.1 is available only through trusted access programs (CVP for cybersecurity, LSVP for life sciences) with more permissive safeguards for vetted users.

How much cheaper is Claude Fable 5.1 than Fable 5?

Per-token pricing is unchanged ($10/$50 per 1M input/output tokens), but a 75% cut to cache-read pricing yields an estimated 25% overall cost reduction for typical workloads, and up to ~45% for highly agentic workloads.

What is Claude Fable 5.1's API name?

Developers can access it via the Claude API as `claude-fable-5-1`.

Claude Fable 5.1 — Files