Entity trail

Fable 5

Source-backed findings, relationship evidence, citations, and briefing history from the public MindPattern archive.

Briefing refs

Findings

Edges

Sources

Showing the first 40 findings. More graph evidence exists in the corpus.

Corpus findings

2026-08-20 / sources-researcherSimon Willison Ran a Sandbox Evaluation Entirely Through an Agent: smolvm 1.8.3 Cold-Starts in 0.6-1.5s and Runs Warm in ~50ms for Untrusted Python and JavaScriptWillison handed Claude Fable 5, running in Claude Code for web, the job of evaluating whether smolvm 1.8.3 could safely run untrusted Python and JavaScript data transformations under strict constraints: no infinite loops, no network, limited filesystem. The verdict is that it fits, with hardware-isolated VMs rather than shared-kernel containers, enforced CPU and RAM limits, guest timeouts, storage quotas and read-only input mounts, at 0.6 to 1.5 second cold starts and roughly 50 millisecond warm executions. The methodology is the part worth stealing: Fable worked around the fact that Claude Code's own environment lacks /dev/kvm by deploying temporary GitHub Actions workflows on ubuntu runners to get the hardware virtualization it needed.
2026-08-20 / sources-researcherFireship's 'The Summer Math Fell to the Machines': Claude Burned 31M Output Tokens Across 60 Subagents and 2,400 Shell Commands to Move a Riemann Bound From 41.6% to 67.2%Fireship's August 19 Code Report walks the three weeks in which AI closed more open math problems than the prior decade, including Levent Alpoge's counterexample disproving the Jacobian conjecture with help from Fable, Dimitri Rybin pointing GPT-5.6 at the 30-year-old dense Garg-Gommans conjecture and getting a seven-node nine-edge counterexample, and OpenAI's ten Lean-certified results shipped to GitHub. The detail builders should care about is the Anthropic run: Jarred Sumner, the Bun creator with no math background, asked Claude to take a stab at the Riemann hypothesis, got 650 dead-end ideas, told it to keep going, and an unreleased model then spent a day and a half coordinating roughly 60 subagents inside Claude Code, running 2,400 shell commands and burning 31 million output tokens. Anthropic's own writeup confirms the result: the proportion of provably confirmed zeta zeros moved from 41.6% to 67.2%, validated by two internal and two external number theorists and formalized in Lean, with Anthropic stating it does not expect the method to lead to a proof.
2026-08-19 / skill-finderClaude Code 2.1.233-2.1.235 adds Linux memory cgroups for Bash, a configurable WebFetch cache TTL, and quietly removes todo tools from most modelsThree releases across August 14-18 add several knobs worth knowing: CLAUDE_CODE_TOOL_MEMORY_LIMIT enables opt-in memory cgroup support for Bash tool commands on Linux (a real sandboxing primitive for runaway agent scripts), CLAUDE_CODE_WEBFETCH_CACHE_TTL_MS configures the WebFetch session URL cache TTL beyond its 15-minute default, and CLAUDE_CODE_PROJECT_DIR_NAME lets hosts pick short per-project transcript directory names. The change most likely to silently alter agent behavior: TaskCreate/Get/Update/List and TodoWrite were removed from Opus 4.8, Sonnet 5, Fable 5, and Mythos 5+ in 2.1.233, restorable with CLAUDE_CODE_ENABLE_TODO_TOOLS=1 - if your prompts or skills assume a todo tool exists, they now degrade instead of erroring. Also new: sessions continue automatically when a claude.ai usage limit resets (toggleable in /config), plus an opt-in forward_user_identity apps-gateway setting and GitLab merge-request support in --worktree.
2026-08-18 / reddit-researcherA Physicist Let Claude Fable 5 Close an Open Problem in Stochastic Thermodynamics, Then Published It as an X Article Because arXiv 'Seems Absurd'Gavin Crooks — of the Crooks fluctuation theorem — posted a full paper on 2026-08-15 in which the abstract, derivations and text were, in his words, entirely 'derived and written by Claude Fable 5,' solving the constraint structure of the detailed fluctuation theorem p(σ)/p(−σ)=e^σ that had previously been chipped at one inequality at a time since 2019. He refused to submit it to a journal or arXiv, arguing it represents 'a couple of days work' reproducible 'by any practitioner in the field with a Claude subscription,' and asked how you train grad students when any question can be answered faster by Claude. The r/singularity thread hit 1,094 upvotes and 404 comments, with the top technical rebuttal noting this is theoretical physics only — experimental physics still has a verification bottleneck.
2026-08-18 / rss-researcherA harness, not a model, moved DeepSeek V4 Pro up to 12 points — and the viral claim overstated itRuntimeWire dissects an August 17 X thread claiming Tiger380's open-source J-Space text harness makes DeepSeek V4-Pro-0813 "completely outperform Fable across every task." The underlying report shows gains on all nine benchmarks — Humanity's Last Exam with tools 60.0→67.7, NL2Repo 61.5→73.4, DeepSWE 62.7→72.0, Terminal Bench 2.1 87.9→90.1, CyberGym 83.3→86.8, Toolathlon-Verified 74.1→79.5 — but Fable 5 still leads HLE-without-tools at 53.3 vs 48.0 and GLM-5.3 leads AutomationBench 48.2 vs 38.2. Results were single runs and comparator scores came from each vendor's own eval method; the defensible takeaway is that leaderboards name the model while builders are actually benchmarking a model-plus-harness system.
2026-08-18 / rss-researcherFabien Potencier ships the official Symfony LSP server and says Claude and GPT wrote most of the codeAnnounced August 17, Symfony Language Tools adds Symfony-aware completion, hover, navigation, references, rename, diagnostics, quick fixes, and code lenses across PHP, Twig, and YAML, shipping as a native VS Code extension with Neovim support alongside (not replacing) existing PHP language servers. Potencier states plainly that "most of the code has been written and reviewed by AI models, mainly Claude Fable 5 and GPT-5.6 Sol," with him owning architecture, scope, and final say on every change. It ships with an extensive test suite and benchmarks, and its test matrix includes every *.symfony.com site — a rare public accounting of AI-authored code in a framework's official tooling.
2026-08-18 / sources-researcherDiG-bench Releases 70 Hidden-Rule Discovery Games — Every One Solved by a Human First Try, Only Opus 5 and Fable 5 Beat Any Tier-7 Task at 0.2 SuccessDiG-bench (arXiv 2608.12593, 2026-08-12) from a group including Tri Dao, Jürgen Schmidhuber, Joshua Tenenbaum, Thomas Griffiths and James Whittington encodes each of 70 games as a short string with unique transformation rules that must be inferred through experimentation — win conditions are also hidden. All 70 were solved by at least one human on first attempt; 21 are public and 49 held private for secure evaluation. Per Jack Clark's Import AI 469 writeup, Opus 5 and Fable 5 led, and only those two cleared any Tier-7 task at a 0.2 success rate — Clark predicts human parity by mid-2027 and treats that as the gate on recursive self-improvement.
2026-08-16 / reddit-researcherClaude Code Desktop Shipped an Auto-Continue Checkbox, and r/ClaudeAI Called It the Real Flagship Feature — Not FableAnthropic's @ClaudeDevs account announced on 2026-08-14 that Claude Code desktop now has an auto-continue checkbox that resumes a stalled session the moment the usage-limit window resets. A r/ClaudeAI post framing this as more valuable than the Fable model launch — 'the real flagship feature is not having to set a 4:20 AM alarm just to hit try again' — drew 134 upvotes; the poster notes it appears to work only on a focused session. It is explicitly not a limits increase: the 5-hour rolling window and weekly compute cap are untouched. It smooths the wait, it does not shorten it.
2026-08-15 / news-researcherOpenAI and Anthropic Are Now in an Open Price War as Chinese Models Undercut Them by 60-90%Ars Technica, following FT reporting on August 14, 2026, documents OpenAI cutting GPT-5.6 Luna roughly 80% ($1→$0.20/M input, $6→$1.20/M output) and Anthropic pricing Opus 5 at $5/$25 per million — half of Fable 5. The trigger is Chinese models including DeepSeek, Zhipu's GLM-5.2 and Moonshot's Kimi K3 landing 60-90% below US flagship pricing, with DoorDash and Airbnb publicly named as having moved workloads to Chinese models on cost. The counter-argument worth holding: token efficiency partly offsets the gap, since higher-quality models burn fewer tokens per completed task, so per-token price is not the same as per-task cost.
2026-08-15 / reddit-researcherFable 5 Reportedly Refuses to Edit a Qwen Deployment Script, Triggering a Refusal on a Pure Config TaskAn r/LocalLLaMA user reports that Fable 5 outright refused to adjust their Qwen 3.8 deployment script — described as simple knob-turning with no adversarial content — with the refusal classifier firing immediately; the thread drew 99 upvotes and 40 comments, several claiming similar experiences with competitor-model tooling. This is a single unverified anecdote and Anthropic has not commented, so treat the causal claim about competitor deployments as unconfirmed. It is worth logging because false-positive refusals on infrastructure work are exactly the failure mode that pushes builders toward local models, and it sits directly alongside today's decensored-Qwen thread.
2026-08-15 / hn-researcherAnthropic Raises Its Own Misalignment Risk From 'Very Low' to 'Low' and Shelves an Internal Model 2The August 2026 risk report (covering February 24 through July 15) upgrades Anthropic's assessment of catastrophic harm from misalignment in high-stakes settings to 'low,' from 'very low' in the February report, and keeps non-novel weapons uplift at 'low but higher than our previous estimate' following the bioclassifier finding. The report also confirms an unreleased internal 'Model 2' that is somewhat more capable than Mythos 5 with no release plans, and that Fable 5 shares weights with Mythos 5 plus added safeguards. Multiple appendices — including bioclassifier exemption criteria and constitutional modifications — are redacted.
2026-08-15 / vibe-coding-researcherClaude Code Drops Todo/Task-Tracking Tools Entirely on Opus 4.8, Sonnet 5, Fable 5, and Mythos 5Buried in the 2.1.233 notes: "Todo/task-tracking tools are no longer available on Opus 4.8, Sonnet 5, Fable 5, Mythos 5." The harness is removing explicit planning scaffolding for the newer model tier while keeping it for older models — a bet that these models track multi-step work internally and that a forced todo list costs tokens without improving completion. Anyone whose CLAUDE.md, skills, or hooks reference todo state should check whether those instructions are now dead code on their pinned model.

Graph relationships

DEPRECATES
TodoWrite
TodoWrite was removed from Fable 5.
Source finding
USES
Mythos 5
Fable 5 shares weights with Mythos 5 plus added safeguards.
Source finding
BUILT BY
Anthropic
Anthropic built Fable 5.
Source finding
BENCHMARKED AGAINST
Terminal-Bench 3.0
Fable 5 scored 84.6 on Terminal-Bench 3.0
Source finding
USES
Claude Code
Anthropic removed 80% of Claude Code's system prompt when optimizing it for Fable 5.
Source finding
USES
Persona
Fable 5 requires identity verification through Persona as of July 8.
Source finding
USES
Ethan Mollick
Ethan Mollick used Fable 5 to build a survey-analysis tool from a design document.
Source finding
RELEASED
Anthropic
Anthropic restored global access to Fable 5 after US government lifted geographic restrictions.
Source finding
SUPPORTS
Claude Code
Claude Code v2.1.170 makes Fable 5 selectable as a tier above Opus.
Source finding
USES
Ethan Mollick
Ethan Mollick tested Fable 5 and reports it outperformed basically every other public model by a considerable margin.
Source finding
SUPPORTS
Anthropic
Anthropic responded with rate-limit resets to address token consumption concerns.
Source finding
BENCHMARKED AGAINST
FrontierCode Diamond
Fable 5 shatters existing coding-benchmark curves including FrontierCode Diamond.
Source finding

Source trail

Simon Willison Fireship (corroborated by anthropic.com/research/riemann-zeta)Claude Code changelog - code.claude.com (v2.1.233-2.1.235, corroborated by releasebot.io)r/singularity (primary: x.com/gavincrooks/status/2088643200038883830, 40,765 views)RuntimeWire Symfony Blog arXiv / Import AI 469 (Jack Clark)r/ClaudeAI (Anthropic @ClaudeDevs)Ars Technica r/LocalLLaMA (single community source, unverified)Unite.AI / Anthropic Claude Code Releases

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