llm-council-when

name	llm-council-when
description	Decides whether an LLM council (multi-model deliberation/ensemble) beats a single strong model - task-type triage, compute-normalized evidence, cost-per-resolved-outcome, benchmarking both paths on your workload. Use for "should I use multiple models", "is an LLM council/ensemble/debate worth it", "single model vs council". Not for designing the pipeline, picking members, or cutting cost.

LLM Council: When

Purpose

Answer the "should I even do this?" question before anyone designs a pipeline, picks members, or writes a synthesizer prompt. Most tasks do not need a council. The default is a single strong model with a long thinking budget; a council has to earn its extra cost, not just be assumed better.

When to use / when NOT to use

Use this skill when the user is deciding whether to run multiple models and merge their outputs at all — "should I", "is it worth it", "council vs single model" — including when they describe the idea without naming it ("would 3 AIs beat 1 good one?").

Not for:

• Designing the pipeline once a council is already decided on → sibling llm-council-architecture.
• Cutting the cost of an existing council → sibling llm-council-cost.
• Picking which models sit on the council → sibling llm-council-members.
• Generic "which LLM should I use for chat/coding" — that's a single-model choice, not a council-vs-single decision.
• A/B testing prompt variants — that's prompt iteration, not multi-model deliberation.

The decision rule

Default: one strong model, long thinking budget. A council only earns its multiplier when all four hold:

1. Task is hard or ambiguous. Compute-matched gains concentrate on hard items — easy items barely move. See references/evidence.md#core-decision-rule.
2. Task is parallelizable/decomposable, not one sequential reasoning chain. Under equal thinking-token budgets, a single agent often matches or beats debate/ensembles on multi-hop reasoning.
3. Cost of a wrong answer dwarfs the 3–6x inference-cost multiplier a council typically costs.
4. Genuinely heterogeneous members are available. Ensemble accuracy is capped by the rate at which all models fail together — check this on your own candidate pool, don't assume diversity.

If any one of these fails, stay with the single strong model.

Workflow

1. Ask what the task actually is. Get the user to state whether it's a routine/easy task or a genuinely hard/ambiguous one, and whether it can be decomposed into independent sub-parts or is one long reasoning chain.
2. Check the four conditions above explicitly, one by one, against what the user tells you. Don't skip straight to a verdict.
3. Apply the methodological trap check to any evidence offered. If the user cites a benchmark or a prior result showing a council/debate/ensemble wins, ask: were thinking-token budgets equalized between arms? Multi-agent-debate gains that vanish under equal budgets, or that are mostly majority voting in disguise, are the single most common way people over-adopt councils. See references/evidence.md#the-methodological-trap.
4. Reframe economics as cost-per-resolved-outcome, not cost-per-query. Tripling per-query spend can be net cheaper if it meaningfully cuts a costly downstream error rate — but only if that downstream cost is actually instrumented, not assumed.
5. Prefer escalation over all-or-nothing. In most real cases the right answer isn't "council" or "single model" — it's triage: single model for the easy majority, council only for the flagged hard/high-stakes tail. (The routing/gate design itself belongs to llm-council-cost.)
6. If the use case is evaluation/judging rather than generation, note that councils of judges are comparatively well validated for that specific job — see references/evidence.md#when-councils-do-win. Don't let a "councils are validated for judging" result get used to justify a generation council.
7. Recommend benchmarking on the user's own workload before committing either way — see Output spec below.

Output spec

A complete answer:

• A clear default recommendation (single model, unless conditions justify otherwise) with the specific condition(s) that do or don't hold for this task.
• If a council-favoring benchmark was cited, an explicit check of whether it was compute/token-budget matched.
• A cost-per-resolved-outcome framing, not a bare per-query cost comparison.
• If the task has an easy/hard split, a note recommending triage/escalation rather than an all-or-nothing choice.
• A short evaluation protocol the user can run on their own workload:
  1. Run the same task set through both the single-model and council paths.
  2. Blind-score both with a judge model used in neither path.
  3. Add human A/B preference sampling.
  4. Hold token budgets equal, or declare the comparison unproven.
  5. Measure the candidate pool's co-failure rate on the user's own eval set before scaling member count.

Failure modes & gotchas

• Taking a "council wins" benchmark at face value. Check token-budget parity first — this is the single highest-leverage question to ask.
• Assuming homogeneous models are diverse. Same-family models sharing a training pedigree correlate more than pairwise-correlation metrics suggest; the co-failure rate (all models wrong together) is the number that matters, and correlation metrics underprice it.
• Confusing "council of judges for evaluation" with "council for generation." The former has real, replicated support; the latter mostly doesn't yet.
• Treating auto-generated/ad-hoc multi-agent scaffolding as free. It has been shown to underperform plain CoT + self-consistency at several times the cost when not purpose-built.
• Ignoring sycophantic conformity in homogeneous debate. Models in a debate can converge on a wrong shared answer rather than correct each other.

References

• references/evidence.md — full evidence base with citations, discarded/ unverified claims, and a table of contents.

Siblings

• llm-council-architecture — designs the pipeline once a council is decided on.
• llm-council-members — picks council composition and diversity.
• llm-council-aggregation — combines member answers into one output.
• llm-council-cost — gates/routes to cut an existing council's cost.
• llm-council-prompts — writes stage-specific prompts (debate, synthesis, judge).
• llm-council-failure-modes — defenses against conformity, collapse, and drift.
• llm-council-harness — headless CLI implementation of a council.