Claude Fable 5.1
anthropic/claude-fable-5.1claude-fable-5-1claude-fable-5.1fable-5-1fable-5.1- 📏 1M-token context window, up to 128K output tokens per response.
- 🧠 Always-on adaptive thinking with selectable effort levels.
- 🔧 Gains focus on long-running agentic coding, refactors, migrations, debugging.
- 📚 Stronger multistep research and document, spreadsheet and slide work.
- 🎯 Anthropic reports a partner's RedlineBench rising 47.9 to 57.0 versus Fable 5.
- 👁️ Multimodal input, function calling and web search per catalog capabilities.
- 🔒 Breaking changes: forced tool use errors; edited turns invalidate thinking blocks.
- 🏢 Released August 2026 alongside Anthropic's Mythos 5.1 variant.
Anthropic PBC is an American artificial intelligence company headquartered in San Francisco. Structured as a public benefit corporation, the lab develops large language models under the Claude name, with a research emphasis on building reliable, steerable, and safety-focused AI…
Explore 18 more models by Anthropic →Claude Fable 5.1 is Anthropic's August 2026 point release in the Fable line, aimed at demanding reasoning and long-horizon agentic work. Anthropic's platform documentation suggests starting most workloads on Claude Opus 5 and moving to Fable 5.1 when evaluations at higher effort settings still fall short. It ships alongside Mythos 5.1, which Anthropic describes as the same underlying model served under different safeguard levels.
Against its direct predecessor Claude Fable 5 — now marked legacy in Anthropic's docs — the company frames 5.1 as an across-the-board improvement whose margin widens at higher effort levels, with gains concentrated in agentic coding across hours-long sessions (multi-file features, large refactors and migrations, debugging, code review), multistep research, and document, spreadsheet and slide production. Anthropic's launch post cites a customer's contract-redlining benchmark, RedlineBench, moving from 47.9 to 57.0 relative to Fable 5, attributed mainly to first-turn quality and more concise edits. Anthropic also publishes cost-versus-score curves on Terminal-Bench 4.0 and Terminal-Bench-Science 0.1 across effort settings.
Migration is not fully drop-in. Per Anthropic's release notes, forced tool use now returns an error, earlier models cannot read this model's reasoning traces, editing prior turns invalidates them, and agent loops may see fewer batched tool calls per turn than with Fable 5.
The capability envelope matches Fable 5 broadly: a 1M-token context, 128K maximum output, always-on adaptive thinking, vision, function calling and web search, with plans and summaries that tend to be more concise. Anthropic says it is working to bring these improvements to other lines, such as Claude Sonnet 5.
This About section is AI-generated from public sources via VeniceStats + Venice inference, with no human editing. It may contain inaccuracies.
Daily usage · Claude Fable 5.1 · Organic sellers
Top sellers · Claude Fable 5.1 · Organic
- ▲ Apex Ant20.8%
- GesundAI18.1%
- Quartz17.3%
- ZLKPro-Api9.9%
- Best7.3%
- Catastrophic5.9%
- Others20.7%
| Seller | Health | Rep↓ | Sales | Tokens | Routing | Input $/M | Cached $/M | Output $/M | Save | 1st token | tok/s |
|---|---|---|---|---|---|---|---|---|---|---|---|
| GesundAI 0x983e…d826 | healthy | 93.38 | $244.07 | 660.62M | #1 | $0.45 | $0.35 | $1.15 | −96% | 4.6 s | 468 |
| Super SeederSAME 0xd19f…41f3 | healthy | 89.22 | $25.44 | 2.58M | #6 | $12.5002 | $0.3125 | $62.5012 | — | — | — |
| 💬 BanterSAME 0x4122…e194 | healthy | 82.88 | $8.70 | 1.76M | #5 | $6.95 | $0.174 | $34.80 | −30% | — | — |
| ▲ Apex AntSAME 0x73b4…e736 | healthy | 81.71 | $280.80 | 173.58M | #3 | $5.00 | $0.13 | $25.00 | −50% | — | — |
| Relay Works 0x3040…7139 | — | 54.66 | $28.79 | 8.36M | gated | $6.50 | $0.1625 | $32.50 | −35% | — | — |
| Vikey SellerSAME 0xe4c4…3c7b | healthy | 16.82 | $3.66 | 2.46M | gated | $3.00 | $0.30 | $12.50 | −70% | — | — |
| Unified Rack · DeepSeek 240 tok/s 0x42d1…822f | healthy | 13.21 | $0.11 | 8.20k | gated | $9.00 | $0.225 | $45.00 | −10% | — | — |
| OpenCheapSAME 0x0ee1…6c41 | — | 12.43 | $1.19 | 117.02k | gated | $4.90 | $0.1274 | $24.50 | −51% | — | — |
| bartly.eth64.de 0x666e…4666 | healthy | 7.22 | $0.14 | 3.64M | gated | $0.15 | $0.0075 | $0.75 | −99% | 21.2 s | 386 |
| Inference Ready 0x6eb5…ad9a | — | 7.13 | $0.35 | 977.34k | gated | $0.3198 | $0.3198not advertised | $0.9207 | −97% | — | — |
| TokenSaleDIFF 0x2060…742d | — | 0.24 | $1.82 | 2.95M | gated | $0.48 | $0.19 | $2.016 | −95% | — | — |
| surplus-hive 0x6145…5c58 | — | 0.00 | — | — | gated | $30.3819 | $30.3819 | $121.5278 | — | — | — |
| Open Ant 0xe4f6…5bc4 | — | 0.00 | — | — | gated | $12.00 | $0.30 | $60.00 | — | — | — |
| incharge-austin 0x5938…ac97 | — | 0.00 | $0.00 | 21.00 | gated | $9.50 | $0.2375 | $47.50 | −5% | — | — |
| Open BirdSAME 0xc0f1…8183 | — | 0.00 | $7.61 | 963.39k | gated | $7.00 | $0.175 | $35.00 | −30% | — | — |
| LLMartSAME 0x948a…a000 | — | 0.00 | $0.77 | 133.59k | gated | $6.94 | $0.1686 | $34.79 | −31% | — | — |
| Fire Ant 🔥🐜SAME 0xbe05…bc5d | — | 0.00 | $6.24 | 1.00M | gated | $6.49 | $0.1569 | $32.49 | −35% | — | — |
| Flash 0x0329…9b2c | — | 0.00 | —excluded | — | gated | $6.00 | $6.00not advertised | $30.00 | −40% | — | — |
| Joi Gateway 0x8a90…7007 | — | 0.00 | — | — | gated | $5.49 | $5.49 | $27.45 | −45% | — | — |
| Catastrophic 0xefbf…8908 | — | 0.00 | $80.30 | 222.59M | gated | $0.45 | $0.35 | $1.15 | −96% | — | — |
| Hana Gateway ✅DIFF 0x4ae1…117b | healthy | 0.00 | $66.11 | 65.68M | gated | $0.45 | $0.05 | $2.00 | −96% | — | — |
| BestDIFF 0x472f…69fd | healthy | 0.00 | $99.33 | 524.77M | gated | $0.45 | $0.05 | $2.00 | −96% | 0.7 s | 90 |
| Inspectant 0xfc36…8842 | failingupstream error · 55 min | 93.55 | —excluded | — | #2 | $5.00 | $0.125 | $25.00 | −50% | — | — |
| Venice.ai ProxySAME 0x1f22…18c9 | failingupstream error · 3.7 h | 86.84 | $77.38 | 24.18M | #4 | $5.50 | $0.1375 | $27.50 | −45% | — | — |
| attacompute.ai 0xd5e7…7be0 | failingupstream error · 13 h | 51.22 | $8.28 | 3.88M | gated | $3.39 | $0.24 | $16.95 | −66% | — | — |
"Best price" and the seller table are live Antseed catalog data (advertised $/1M tokens — or $ per generated image for unit-billed image models — not settled amounts). Reputation = buyer trust score (0-100, the Antseed SDK's own formula). "Routing" = the SDK's default buyer routing (what the VPR desktop app ships with): a trust ≥ 60 gate on the effective reputation, then cheapest-first among routable sellers; live failover state (per-peer cooldowns) is buyer-side runtime and not included. Model knowledge (TLDR, provider, About) via the VeniceStats enrichment layer. Advertised catalog, not the model used in any specific purchase. "Usage on Antseed" counts only settlements whose buyers share the per-model split on-chain (metadata v2/v3, opt-in), so every usage figure is a lower bound.