add-model

---

name: add-model description: Add or update a model in the harness model registry. Use when the user wants to add a new AI model, update model pricing, or change default models for a harness. argument-hint: [harness] [model-id] disable-model-invocation: true

Add or update a model in the model registry. The user will specify which harness (e.g., codex, claude-code) and what model to add or change.

1. Gather information

Before making changes, confirm with the user:

• Harness: Which harness does this model belong to? (Check HarnessId in projects/harness/src/types.ts for valid values)
• Model ID: The wire ID sent to the CLI (e.g., gpt-5.4, claude-opus-4-6)
• Alias: The short picker alias (e.g., opus, gpt-5.4) — often the same as the model ID for codex models
• Label: The human-readable display label (e.g., GPT-5.4, Opus 4.6)
• Display class: The grouping class for stats/UI (e.g., Codex, Opus)
• Default?: Should this become the new default model for the harness?

If the model name is ambiguous or you're unsure about the exact wire ID, test it locally first by running the harness CLI. For codex:

codex exec -m <model-id> "echo hello" 2>&1 | head -15

For claude-code, check Anthropic's model docs or test with claude.

2. Look up pricing

Search the web for the model's official per-million-token pricing:

• Input price per 1M tokens
• Output price per 1M tokens
• Cached input price per 1M tokens (if available)

Use the provider's official pricing page as the source of truth.

3. Update all required files

Every model addition touches these files — all must stay in sync:

a. Model Registry (static catalog)

File: projects/harness/src/models.ts

Add a ModelEntry to the appropriate harness in MODEL_REGISTRY. If making it the default, update defaultModel.

b. Harness class models() method

The harness class must return identical data to the registry. A sync test enforces this.

• Codex: projects/harness/src/harnesses/codex/index.ts — the models() method
• Claude Code: projects/harness/src/harnesses/claude-code/index.ts — the models() method

c. Pricing table

Each harness has its own pricing file:

• Codex: projects/harness/src/harnesses/codex/pricing.ts — add entry to CODEX_PRICING
• Claude Code: projects/harness/src/harnesses/claude-code/pricing.ts — add entry to CLAUDE_PRICING

d. normalizeModelClass() fallback

File: projects/harness/src/models.ts

If the new model ID doesn't match existing string-based fallback patterns (e.g., a codex model that doesn't contain "codex" in its name), add a fallback line. The function first checks the registry, then falls back to substring matching for legacy/effort-suffixed IDs.

e. Tests

File: projects/harness/src/models.test.ts

Update:

• Model count for the harness
• Expected model ID list
• Default model assertion (if changed)
• normalizeModelClass assertions if new fallback patterns were added

Also check projects/harness/src/harnesses/<harness>/pricing.test.ts for any pricing test expectations.

4. Verify nothing else needs updating

The web UI reads dynamically from MODEL_REGISTRY so typically no frontend changes are needed. But check for hardcoded model IDs in:

• projects/web/src/constants.ts
• projects/web/src/components/ModelPicker.tsx
• projects/web/src/store/TaskModel.ts
• projects/web/src/hyperplan/ (test fixtures may reference specific models)

These usually don't need changes but verify.

5. Run tests

Run the harness unit tests (excluding slow integration tests):

cd projects/harness && npm run test

All tests must pass before committing.