Core concepts

Stac is organized around three objects: accounts, stacks, and API keys.

Account#

Your account is your identity and billing entity. It doesn't hold configuration by itself — everything that affects how requests behave lives on a stack.

Stack#

A stack is one deployed model, running on capacity sized to a plan. An account can have multiple stacks, each on its own plan, each with its own configuration:

• Plan — Go, Pro, Max, or Enterprise. Fixed per stack; it determines the model and the capacity behind it.
• System prompt — optional, scoped to this stack only.
• Knowledge base — documents you upload for retrieval, also scoped to this stack. The collection belongs to the stack; which keys search it is a per-key setting.
• API keys — each key belongs to exactly one stack.

Requests never choose a model — the stack you're calling already has one assigned, and any model field you send is ignored.

API keys#

A key authenticates requests against one specific stack. Keys are prefixed stac_ and shown in full only once, at creation — Stac stores a hash, not the key itself. A key can optionally be given an expiration date; after that, requests with it are rejected.

Each key also carries its own configuration, independent of the others on the same stack: its own system prompt, generation parameters, and whether it searches the stack's knowledge base. That is what lets one stack serve different uses — the automation key searches the collection, the coding-tool key does not — without changing the code calling the API.

Next steps#

• Authentication — key format, expiration, error responses.
• Pricing model — what each plan includes.
• API reference — every request parameter.