Model Routing Policy

Status: adopted Last updated: 2026-09-05

This document defines the default model and reasoning-effort routing for Claude Code, Codex, Cursor, and Grok in Harness workflows.

Decision

Use explicit role tiers, not prompt-text inference.

Harness must route model and effort from the workflow role:

• lite: cheap, read-heavy, low-risk work
• standard: ordinary implementation and setup
• worker: Breezing implementation and retry work
• deep: architecture, security, cross-repo, migration, and failure recovery
• review: quality gates and adversarial checks
• release: procedural release and public-surface checks
• long-context: large repository or long-session context work

Do not infer effort from free-text markers such as "think harder". A caller may still ask for one-off deeper reasoning, but durable routing belongs in config, agent frontmatter, or wrapper arguments.

Official Evidence

Claude Code supports model aliases and explicit model IDs. The legacy opusplan alias uses Opus in plan mode and Sonnet in execution mode; the September routes below select Fable 5.1 explicitly. Claude Code settings can pin model, restrict availableModels, and set default alias targets through ANTHROPIC_DEFAULT_*_MODEL environment variables. Official docs: https://code.claude.com/docs/en/model-config

Claude Code effort is configurable through /effort, /model, --effort, CLAUDE_CODE_EFFORT_LEVEL, effortLevel, and skill/subagent frontmatter. Frontmatter overrides the session level, while CLAUDE_CODE_EFFORT_LEVEL overrides both. Official docs: https://code.claude.com/docs/en/model-config

On the verified Claude Code 2.1.261 runtime, a saved