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reference pattern/framework Orchestration prompting for Claude 5-era models (Fable 5, Opus 4.8, Sonnet 5) What Anthropic's model-page guidance says about delegation, token efficiency, and rule phrasing for current-generation orchestrators — and how it invalidates delegation rules written for cheaper/older main-loop models. Answers: how should an orchestrator rule doc be written when the main loop is a top-tier model?
type/reference
domain/ai-agents
domain/orchestration
tool/claude-code
global 2026-07-08 2026-07-08 2026-07-08
agent-orchestration-patterns
agent-orchestration-cookbook
os-orchestration-ws1-session-audit-results
cc-os

Orchestration prompting for Claude 5-era models

Sources: Anthropic model pages (prompting-claude-fable-5, prompting-claude-opus-4-8, prompting-claude-sonnet-5, claude-prompting-best-practices), fetched 2026-07-08. Community claims below are marked [unverified claim].

The meta-finding (why this note exists)

Delegation rules go stale when the main-loop model tier changes, even if every rule is still individually true. A rule doc written to prevent over-delegation on a sonnet main loop (where direct work is cheap and Opus 4.6-era models over-spawned) actively suppresses delegation on a Fable/top-tier main loop, where every direct tool call is billed at the most expensive rate. The threshold question is not "is this task big enough to delegate?" but "does this work need main-loop-tier judgment?" — cost asymmetry between the orchestrator and the cheapest adequate executor must be explicit in the rule text, not implied.

Load-bearing guidance from the model pages

  1. Calibrated trigger phrasing, both directions. On 4.6+ models, absolutist wording ("CRITICAL: you MUST...") over-fires; plain "use X when Y" is correct. Crucially, the canonical best-practices delegation snippet pairs a positive trigger list ("use subagents when parallel / isolated context / independent workstreams") with a negative one ("work directly for simple tasks, sequential ops, single-file edits, shared-state steps"). A rule doc phrased negative-first ("delegate ONLY when...") is read literally by these models and suppresses delegation in every gray zone.

  2. Literal instruction-following. Opus 4.8/Sonnet 5/Fable 5 do not silently generalize an instruction beyond its stated scope. A threshold like "≤2-tool-call ops are direct" licenses 3+-call direct work forever unless something obligates delegation above some line — write both sides of the boundary.

  3. Model biases differ by generation and must be steered per-model: Fable 5 dispatches parallel subagents readily and sustains async communication with them (recommended pattern: "delegate independent subtasks and keep working while they run" — non-blocking); Opus 4.8 under-delegates by default and needs explicit "spawn multiple in the same turn when fanning out" nudges; Opus 4.6 over-delegated. The same orchestration text lands differently per main-loop model.

  4. Effort is the primary within-model cost dial — the docs give no cross-tier haiku/sonnet/opus decision table at all; they treat effort as the main quality/cost lever. An orchestration policy that routes only by model tier is missing a lever: mechanical subagent work → low effort, hard verify/judge stages → high/xhigh (where the harness exposes it, e.g. Workflow agent() opts).

  5. Long-lived / batched subagents amortize cost. Fable 5 page: long-lived subagents that keep context across subtasks save time and cost via cache reads and avoid bottlenecking on the slowest agent. Combine with the batching economics in agent-orchestration-patterns (tool tax ~2025K tokens per spawn; batch 58 similar items per specialist; reuse a live agent for follow-ups instead of spawning fresh).

  6. Front-load the task spec. Opus 4.8/Sonnet 5: token use rises in interactive settings because the model re-reasons after each user turn; a complete task/intent/constraints statement in the first turn is cheaper and better than progressive disclosure. Applies equally to subagent prompts: one complete grouped prompt beats iterative follow-ups.

  7. Grounding and downgrade honesty. Fable 5 page's "audit each claim against a tool result" pattern nearly eliminated fabricated status reports in Anthropic's testing — the same mechanism as subagent model self-report (subagents know their model ID; launch results don't show it).

Community pattern (context, not evidence)

The "Fable-5 orchestrator" community pattern (pasqualepillitteri.it, 2026-07-02) matches the above architecture — Fable plans/synthesizes, pinned-model personas execute, orchestrator generates only 1020% of tokens, "510× savings" [unverified claim] (all cost figures asserted without methodology; the one external attribution, "MindStudio 8090% shift with no quality loss," has no citation). Its mechanical details (frontmatter-pinned model: in ~/.claude/agents/, description-driven delegation) are real Claude Code mechanics; its numbers are not evidence.

How to apply

When writing or reviewing an orchestrator rule doc:

  • State the cost asymmetry explicitly and key the delegation threshold to the main-loop tier (models know their own model ID, so tier-conditional rules are implementable).
  • Pair positive and negative delegation triggers; never "only when."
  • Add a batching rule (group related subtasks into one agent prompt; reuse live agents) and an async rule (keep working while subagents run).
  • Re-audit the rule doc whenever the default main-loop model changes generation — evidence gathered under the old economics (e.g. "direct work was often superior") may no longer bind.