Choose a model
Switching models, and when the choice is made for you.
Every conversation runs against a model. AODex ships a default, and the model picker in the conversation header changes it.
Before you start: the models available to you come from your account. If the list is empty you will see No AI models are available yet — that is an account or availability problem, not a setting you can fix in the picker.
Switching
Open the model control in the conversation and pick another. The change applies to subsequent messages in that thread; earlier replies keep whatever produced them. AODex confirms with Switched to ….
When a persona overrides you
A persona can pin a model. When one does, the picker shows Model is fixed by this persona and will not let you change it — that is the persona doing its job, not a fault.
To change the model in that case, either edit the persona or switch to one that leaves the choice open. See Personas.
Defaults
Default model in Preferences sets what new conversations start with. Individual threads can still diverge from it.
A persona may also carry a Persona default — the model it prefers without hard-pinning it. That applies when the persona is selected and you have not chosen otherwise.
Choosing well
The honest guidance is that most work does not need the largest model. Reach for a bigger one when the task is genuinely hard — multi-step reasoning, subtle code, long synthesis — and leave it alone otherwise.
If a specific answer is disappointing, changing the model is one lever, but extended reasoning and a better system prompt are often the ones that actually move it.