Models

Sigil uses four model tiers, each configured on the graph and rebound on every run:

Tier	Role	Key
`chat`	user-facing conversation + sub-agents	`chat_model` (falls back to `frontier`)
`frontier`	compiles new skills	`frontier_model`
`small`	executes compiled skills	`small_model`
`router`	routes a task to a skill	`router_model` (falls back to `small`)

The division of labor: the strong model is what you talk to. Chat is the user-facing surface and has no compiled procedure to lean on, so chat (and frontier, which authors skills) should be a strong model. The cheap model (small) is reserved for executing an already-compiled skill — a structured procedure it just follows — and for routing. That's the whole thesis: pay the strong model to think and to build harnesses; let the cheap model ride them.

Set one with configure <tier>_model <name>, sigil models set <tier> <name>, or /model <tier> <name> in chat.

Model names

Model names are litellm strings (via byLLM), so every provider litellm supports works:

Provider	Example name	Auth
OpenAI	`gpt-4o`, `gpt-4o-mini`	`OPENAI_API_KEY`
Anthropic	`claude-sonnet-4-6`	`ANTHROPIC_API_KEY`
Google	`gemini/gemini-2.0-flash`	`GOOGLE_API_KEY`
Ollama (local)	`ollama_chat/qwen3:8b`	none — local daemon
Claude Code CLI	`claude-cc/opus`	none — your Claude Code login

The frontier tier needs its provider key; the small/chat tiers can be fully local. A weaker chat model tends to over-reach for tools — if chat behaves oddly, try a stronger chat_model.

litellm itself is provisioned by jac install, from the llm capability that jac's config resolver switches on when it sees the top-level [byllm] table in jac.toml (it stopped being bundled in the runtime closure in jac 0.36). If every model call fails identically — regardless of tier, provider or key — that section is what to check; install.sh verifies it, and jac install --plan should list litellm.

No key at all: your Claude Code CLI

--claude puts every tier on the Claude Code CLI you already have installed, using your own subscription instead of a provider key:

sigil --claude compile ./SKILL.md

Full details, costs and limits: claude-code.

Aliases and fallbacks

sigil models list                          # tiers, aliases, fallback chains
sigil models alias fast gpt-4o-mini        # friendly name -> model
sigil models fallback chat gpt-4o-mini,ollama_chat/qwen3:8b   # failover chain

A tier with a fallback chain is bound to a byLLM ModelPool (strategy="fallback") that fails over primary → fallbacks.

Web search providers

Open-web search (web_search) is not an LLM tier. Sigil tries three routes, in order:

Brave — BRAVE_API_KEY (free tier at brave.com/search/api)
Firecrawl — FIRECRAWL_API_KEY
Claude Code's own WebSearch — no key, but only in claude mode (sigil --claude …)

A direct search API is faster and cheaper than a model turn, which is why the keyed providers come first. The third route exists so that claude mode needs no second signup: the machine already has a search-capable agent you are paying for. See claude-code.

With none of the three, web_search returns setup guidance; web_fetch still works on any public URL, including keyless JSON APIs like GitHub's.