KeiSeiKit-1.0/_primitives/_rust/kei-model-router

kei-model-router

Model selection (Haiku 4.5 / Sonnet 4.6 / Opus 4.7) for Claude Code Agent spawns. Empirical-posterior decision rule keyed on task-class DNA + Beta posterior + cost minimization, with kernel-smoothing for unseen task classes.

Math

Decision rule:

m*(d̂) = argmin_{m ∈ M} { c(d̂, m) | P[q(d̂, m) ≥ q*] ≥ 1 − δ }

Empty feasible set → fallback (top tier) per RULE -1 NO DOWNGRADE.

Posterior: q(d, m) ~ Beta(α₀ + n⁺, β₀ + n⁻) with uniform prior. n⁺ counts rows where outcome='functional' AND escalation_depth=0; n⁻ everything else.

Kernel-smoothed transfer for unseen task classes:

K(d, d') = α_role · 1[role=role'] +
           α_caps · |caps ∩ caps'| / |caps ∪ caps'| +
           α_scope · 1[scope=scope'] +
           α_body · jaccard_bigram(body, body')

Verified pricing

[VERIFIED: https://platform.claude.com/docs/en/docs/about-claude/pricing 2026-04-30]

Model	Input/MTok	Output/MTok
Haiku 4.5	$1.00	$5.00
Sonnet 4.6	$3.00	$15.00
Opus 4.7	$5.00	$25.00

Opus 4.7 uses a new tokenizer that may produce up to 35% more tokens on identical text — multiply quote accordingly when comparing against Haiku/Sonnet on the same input.

CLI

kei-model-router pricing                  # print pricing table
kei-model-router select <agent> [--prompt P]
kei-model-router calibrate                # re-fit kernel weights
kei-model-router --help

Orchestrator integration (Path B — runtime)

Per RULE 0.13, the orchestrator owns Agent spawning. Before spawning a non-trivial agent the orchestrator can consult the router and pass an explicit model parameter:

kei-model-router select code-implementer-rust \
    --prompt "Add multi-tool integration test for parser"
# → model: sonnet (if posterior built up); model: opus (initial fallback)

Then in the orchestrator's Agent invocation:

Agent({ subagent_type: "code-implementer-rust", model: "sonnet", ... })

Until posterior data accumulates the router conservatively returns top-tier (Opus). As outcome column fills via agent-fork-done.sh STATUS-TRUTH parsing, posterior diversifies and cheaper tiers begin to qualify.

Assembler integration (Path A — compose-time, deferred)

Rebaking the model into generated .md files at assemble time is deferred. Current default model: opus in 55/55 manifests is safe; adopt Path B (orchestrator discipline) until ledger has ≥100 outcome-tagged rows per common task class.

Cubes

File	LOC	Concern
pricing.rs	167	Verified per-MTok constants (microcents)
dna_class.rs	113	DNA component extraction (role/caps/scope)
complexity.rs	178	τ-estimator (heuristic regex+role+length)
posterior.rs	197	Beta posterior from ledger + Wilson lower b.
kernel.rs	134	Substrate similarity kernel for unseen DNAs
escalate.rs	73	Retry-ladder bookkeeping
select.rs	197	Decision rule (argmin cost s.t. q_lb ≥ q*)
calibrate.rs	193	Offline LOO weight refit (grid search)
main.rs	142	CLI dispatch
lib.rs	35	Module barrel + re-exports

All cubes within Constructor Pattern budgets (≤200 LOC, ≤30 LOC/fn).

Schema dependency

Requires kei-ledger schema v9+ which adds:

tokens_in INTEGER
tokens_out INTEGER
stubs_count INTEGER DEFAULT 0
outcome TEXT CHECK (outcome IN ('functional','partial','scaffolding','fail',NULL))
escalation_depth INTEGER DEFAULT 0
task_class_dna TEXT GENERATED ALWAYS AS (...) VIRTUAL
INDEX idx_agents_task_class ON agents(task_class_dna)

Hooks

• agent-fork-logger.sh (PreToolUse:Agent, advisory) — writes 'running' row with DNA at spawn.
• agent-fork-done.sh (PostToolUse:Agent) — closes row + parses STATUS-TRUTH MARKER from agent's tool_response → updates outcome, stubs_count, tokens_in, tokens_out.

Lock

2026-04-30. Phases 1-9 of kei-model-router rollout complete (Phase 9 orchestrator-discipline; assembler refactor deferred until ≥100 outcome-tagged rows accumulate).