Switch agents and models
Choose the agent, account, model, speed, and effort for a chat, hand a chat to another agent, or fork it.
Every chat has one control for where it runs and what it runs on: the model picker in the composer. Change your mind at any point, even in the middle of a conversation.
The model picker
Click the model picker in the composer to open Model settings. From here you choose the model, speed, and reasoning effort for this chat.
- Model lists the models available to the chat. On Claude Code or Codex CLI, that includes the agent's own models once the account is signed in, alongside your Mach Studio models. OpenCode lists your Mach Studio models and any provider you signed in to.
- Harness sits below the model row. It lists Default (the built-in agent) and every account you have signed in to, grouped by agent. Before the first message, picking one simply sets where the chat will run.
Hand a chat off mid-conversation
Once a chat has messages, choosing a different agent or account under Harness hands the conversation off. The new agent picks up with the full context, and your next message continues from where you left off. A line in the transcript records the switch, for example Handed off from Claude Code to Codex CLI; hover it to see which account was signed in.
You can also right-click a chat in the sidebar and choose Hand off to. Switching between two accounts of the same agent carries the session itself over.
Speed and effort
Under Speed, pick Standard or Fast. On Mach Studio models, Fast gives higher throughput and uses more credits; the picker shows how much. On Claude Code and Codex CLI, Fast uses the agent's own faster mode, and the picker says Unavailable in this agent version if your installed version does not offer it.
The Effort slider sets how hard the model thinks, from faster to smarter. Claude Code and Codex CLI offer their own reasoning levels here. Models that do not reason hide the slider.
Fork a chat
Forking copies a conversation into a new chat so you can try a different direction without losing the original.
- Hover an assistant message and click Fork chat to copy the conversation up to that point.
- Right-click a chat in the sidebar and choose Fork to copy the whole conversation.
The forked chat keeps the same agent and account until you change them. Wait for a chat to finish responding before forking it.