Model and reasoning
The engine that powers the agent. Fast models are included; the most powerful ones activate with your own provider key.
In the Brain tab, a selector opens the list of models, arranged in two sections. Here is exactly what you see:
Included: nothing to configure
The fast models (GPT-5.4 Nano and Mini, Claude Haiku, Gemini Flash) run on Magnitude's keys. They are enough for the vast majority of conversations: they are ready out of the box, with no key and no extra cost.
Premium: your own key
The most powerful models (GPT-5.4, Claude Sonnet and Opus, Gemini Pro) are activated by connecting the API key from your own OpenAI, Anthropic or Google account, in Settings › AI Models. You are billed directly by the provider, at the listed rate (input / output per million tokens). Until a key is added, these models stay locked.
A key you add is never shown again: the system only indicates whether a provider is connected, never the key itself.
The reasoning level
On the models that support it (the GPT-5 family), a slider sets the reasoning level: from "fast" to "thorough". The higher it is, the more time the agent takes to reason through complex cases, at the cost of a little latency.