Claude mythos scaffold

Skill kasparovabi/claude-mythos-scaffold

Pattern-based scaffold for systematic AI agent work, with honest capability boundaries. Inspired by observed Claude Mythos Preview behaviors.

Install

npx -y skills add kasparovabi/claude-mythos-scaffold

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One thing to look at

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What its author says it does

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Push Opus 4.x-class and smaller models toward Mythos/Fable-grade agentic behavior. Kernel of Fable-distilled patterns (decomposition, verification, next-action, context economy) plus demand-loaded skills, persistent mission files, named sub-agents, enforcement hooks, and domain modes (research, migration). Use when starting complex multi-step work, long-horizon tasks, or anything needing systematic persistence and verification. Do NOT fully load on Claude 5 models (Fable 5 / Mythos 5 / Opus 5 and later); over-scaffolding degrades them.

SKILL.md

4.3 KB, as published. Nobody here has run it

Mythos scaffold

Agentic discipline framework anchored by working patterns distilled from Claude Fable 5 itself (2026-07-06, revised 2026-07-21). v2 adds a persistent mission file, harness-enforced persistence (Stop/SessionStart hooks), named worker agents with explicit model routing, a headless profile, and an eval harness that measures the scaffold instead of trusting it.

Honest expectation: the scaffold transfers process discipline, not capability. It makes Opus 4.8 a disciplined Opus 4.8. See eval/ for measured deltas.

Model gating (check first)

Session model	What to load
Opus 4.8 / Opus 4.x / Sonnet 4.x / Haiku	Kernel, then tiered (below)
Claude 5 family (Fable 5 / Mythos 5 / Opus 5 / Sonnet 5) and later	Nothing, or at most the kernel's verification section. State goal and constraints; do not enumerate steps.

When in doubt (a model newer than this table): treat it as Claude 5 family — under-scaffolding costs less than over-scaffolding on capable models.

Activation

Always load exactly one file: the kernel, core/fable-distilled.md. It carries the binding rules and the load map for every other file (mode, tool-stack, context-priming, decomposition, agent-loop, verification, failure-recovery, memory, headless, domains). Open others only when their load-map trigger fires.

Mission file

Long-horizon runs externalize state to ~/.claude/mythos/missions/<slug>--<stamp>.md with an active-mission pointer at ~/.cache/mythos/active. The /mythos-mode command owns the lifecycle (<task> / resume / status / close); the hooks in hooks/ read it to block premature stops and to re-surface the mission after compaction. Schema: see the command's mission template.

Sub-agents

agents/ ships four workers installed into ~/.claude/agents/: mythos-scout (haiku, mechanical bulk), mythos-builder (sonnet, light code), mythos-heavy (opus, hard code), mythos-verifier (sonnet, adversarial check, never edits). Every spawn names its model explicitly.

Domain modes

Research: domains/research/ (retrieval tiers, claim graph, cite-verify, output formats)
Migration: domains/migration/ (audit, plan, execute, rollback)

Integration

The scaffold routes to neighbors instead of duplicating them: see INTEGRATION.md.

When to use

Multi-step tasks where the model might stall, drift, or miss verification
Long-horizon research or migrations (domain modes)
Debugging cycles where naive retry fails
Unattended runs (cron, loops): core/headless.md

When not to use

Single tool call, single answer questions: overhead not worth it
Tasks already covered by a more specific skill
Sessions running on Claude 5 family models — Fable 5 / Mythos 5 / Opus 5 / Sonnet 5 (model gating above)

Changelog

2026-07-21 (v0.3): kernel recompiled (mode rules folded in, context economy, escalation protocol); mission file + pointer; Stop/SessionStart enforcement hooks; four named worker agents; headless profile; eval harness (T1 persistence, T2 verification) and distillation curation procedure; command grows resume/status/close; installed command becomes a symlink; stale references fixed; dead sync hook removed.
2026-07-06: Fable-distilled patterns added; read-all-8 replaced with tiered loading; model gating; sub-agent model routing.
2026-04-27: initial 6-skill framework plus research and migration domains.

Source

https://github.com/kasparovabi/claude-mythos-scaffold (MIT, by kasparovabi). Inspired by Claude Mythos Preview behaviors, not affiliated with Anthropic.