Fable

Epoch said an AI-generated solution found a presentation for the absolute Galois group of the 2-adic numbers, marking the second FrontierMath open problem it says AI solved. The result was elicited with Fable 5 and also GPT-5.5 Pro, making it a benchmark milestone rather than a product release.

A U.S. tech adviser accused Moonshot AI of using Anthropic’s Fable to build Kimi K3, while China’s embassy denied related claims. Engineers questioned whether leaderboard results and missing logits fit a simple distillation story.

OpenCode users reported complex DeepSeek V4 API prompts returning Fable-like outputs and CoT style, while simpler prompts did not. The evidence is community-led and disputed, so the claim remains unverified.

Posts citing Anthropic say Fable 5 will stay in Claude Max and Team Premium at 50% of limits. Pro and Team Standard move to credit access with a one-time $100 credit after July 20.

Starting July 20, Fable 5 is included in Claude Max and Team Premium at 50% of plan limits. Pro and Team Standard shift to credit-based access with a one-time $100 credit.

Anthropic said it resolved an issue that made Fable 5 unavailable in claude.ai and Claude Code after users reported lost access or credit prompts. ClaudeDevs said affected extra-usage customers would receive refunds plus matching credits.

Cognition said Devin Fusion now uses Fable 5 and saw lower cost per task than Opus 4.8. Practitioners cited Fable-led delegation patterns that cut token use, with caveats on serial debugging.

Anthropic extended Fable 5 on paid plans and raised Claude Code weekly limits by 50% through July 19 while keeping the half-week cap. Users still described the rolling access changes as disruptive.

Fable-assisted JLens logs and a separate experiment tested how the proposed J-space forms and whether attention gradients into past tokens can be blocked. The reported blocking method worked in the setup but hurt performance, making it a research update rather than an engineering control.

Anthropic says paid Claude plans keep Fable 5 access until July 12, with Fable use capped at 50% of weekly limits. Users still reported exhausted quotas and multiple Max subscriptions as workarounds.

ClaudeDevs reports Sonnet 5 with a Fable 5 advisor reached ~92% of Fable 5's SWE-bench Pro score at ~63% of the price. Other builders route implementation to Sonnet, Codex, GPT-5.5, or GLM workers.

A Fable maintainer set the Claude subscription cutoff for 11:59:59pm PT on July 7 as users posted high Claude Code credit usage. One estimate claimed about $2,267 of usage across two $200 accounts in six days.

Practitioners reported concrete Fable 5 coding outcomes, including sqlite-utils 4.0rc2 for $149.25 and hallucinations in X API and OAuth checks. Failures around tests, finance, production outages, and token-heavy loops kept review systems central.

CAIS and Scale’s Remote Labor Index reportedly put Fable 5 at 16.1% human-accepted freelance tasks, versus 8.3% for Opus 4.8 and 6.3% for GPT-5.5. The same report says AI judges overrated newer models, especially GPT-5.5 and Opus 4.8.

Fable 5 users said Claude Max subscription access runs through July 7, with some reporting it may return only when compute is available. The deadline changed planning for Fable-heavy coding runs and fallback options.

Fable users reported cost escalations from $300/day estimates to a single high-effort prompt above $130 and quota-drain complaints on Reddit. Users also reported automatic Opus fallback and safety refusals tied to bio/cyber safeguards.

Fable 5 users reported Opus 4.8 fallbacks, $600 Max-account rotations, slow browser automation, and token-saving subagents. Watch routing opacity, quota burn, and latency before relying on it for long-running agent work.