Advanced Decision Pipeline

Most apps should use createRouter() and a routing policy. Use the lower-level API when you need to inspect routing evidence, perform the selector call yourself, or persist state between phases.

Prepare And Finalize

prepareRoute(input) does candidate compatibility, cost estimation, decision recovery, strategy pruning, eval matching, and selector-request construction. Then finalizeRoute() parses and validates the selector’s answer.

import { finalizeRoute, prepareRoute, type RouteInput } from "@dari/router-core";

const input: RouteInput = {
  candidateModels: ["openai/gpt-5.4-mini", "anthropic/claude-sonnet-4-6"],
  metadataLookup: (model) => modelMetadata[model]!,
  requiredCapabilities: [],
  strategy: "slm",
  pricing: (model) => modelPricing[model] ?? null,
  messages: conversation,
  chainsByModel: new Map([
    ["openai/gpt-5.4-mini", []],
    ["anthropic/claude-sonnet-4-6", []],
  ]),
  prefixHits: [],
  nowMs: Date.now(),
  toolChoiceFp: "",
  responseFormatFp: "",
  selectorModel: "openai/gpt-5.4-mini",
  selectorContextWindowChars: 400_000,
};

const prepared = prepareRoute(input);
if (!prepared.selectorPreparation) throw new Error("Custom routing rules are missing");

const selectorOutput = await callSelector(prepared.selectorPreparation.selectorRequest);
const result = finalizeRoute(prepared, selectorOutput);
console.log(result.decision);

RouteInput fields

candidateModels — model IDs to consider
metadataLookup — resolves model metadata
pricing — returns model/cache rates or null
messages — the conversation
chainsByModel — prefix hashes per model
prefixHits — stored provider-cache observations
nowMs — timestamp for cache-warmth checks
toolChoiceFp / responseFormatFp — prevent incompatible cache reuse
selectorModel / selectorContextWindowChars — selector config
modelFallbackEnabled / fallbackRequiresDifferentProvider — optional fallback

The host provides all inputs explicitly — Router Core reads no env vars, credentials, database, or clock. route(input, selector) is the convenience composition when you don’t need to interleave work.

Inspect Prepared Evidence

The prepared result exposes:

Compatible model/reasoning pairs
Cache-aware cost estimates (routing evidence, not billing)
Candidates removed by pruning
Recovered previous decision and conversation identity
Warnings from best-effort cost estimation
The exact selector request

Unknown pricing stays unknown, not treated as free.

Selector Output

The selector returns JSON with selected_model, reasoning_effort, and reason. finalizeRoute() validates the selected pair appeared in the prepared candidates. The pipeline can also request a fallback. modelFallbackEnabled controls whether one is required, fallbackRequiresDifferentProvider controls provider diversity. Fallback execution is host-owned.

Cache State

Provider caches make model continuity cheaper than switching. Supply:

chainsByModel — ordered prefix hashes per model
prefixHits — stored provider-cache observations
nowMs — determines if an observation is still warm
toolChoiceFp / responseFormatFp — prevent incompatible cache reuse

A fresh conversation uses empty chains and no hits. After a turn, the host records the serving model, reasoning effort, usage, prefix hash, and decision. prefixChain() creates Chat Completions hashes; optionsFingerprints() creates the expected fingerprint values.

Anonymous Selection

For training or evaluation, prevent the selector from memorizing model names:

import { assignAnonymousActions, anonymizeSelectorInput, parseAnonymousActionSelection } from "@dari/router-core";

const mapping = assignAnonymousActions(candidates, Math.random); // shuffled letter labels
const anonymized = anonymizeSelectorInput(selectorInput, mapping);
const realPair = parseAnonymousActionSelection(anonymizedOutput, mapping);

The second argument is a random source in [0, 1) — pass a seeded PRNG to reproduce recorded permutations. Intended for policy training, not production routing.

Speculative Execution

Because prepareRoute and finalizeRoute are separate, the host can start the compatible previous model while the selector runs. See the Speculative Routing guide for eligibility and failure semantics. A complete no-network example is at examples/basic_route.ts — run it with bun run example:decision-pipeline.

Get Started

Build A Router

Advanced

Advanced Decision Pipeline

Prepare And Finalize

Inspect Prepared Evidence

Selector Output

Cache State

Anonymous Selection

Speculative Execution

​Prepare And Finalize

​Inspect Prepared Evidence

​Selector Output

​Cache State

​Anonymous Selection

​Speculative Execution

Prepare And Finalize

Inspect Prepared Evidence

Selector Output

Cache State

Anonymous Selection

Speculative Execution