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A runtime is the coding agent that does the work in a Kana session. You pick runtimes when you install a machine, and you pick one per session in the agent picker. Kanaeru gives every runtime the same harness of skills, rules, and hooks, so a task follows the same process whichever agent runs it. The ID is what you pass to kana conv send --runtime. Sakana AI’s Fugu runs as a model rather than as its own runtime. When Sakana’s codex-fugu launcher is installed, Codex offers a Fugu model. When claude-fugu is installed, Claude Code offers one too. Both use SAKANA_API_KEY.
You don’t have to set everything up through Kanaeru. The Agent Manager detects runtimes that are already installed on the computer, and reuses the sign-ins they already have, such as an existing claude login or Codex sign-in.

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Provider API keys

You can paste these keys into the install command, or save them later in the machine’s Provider credentials panel. Keys pasted into the install command are only inserted into that command. The Agent Manager stores them locally on the machine.

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Code reviewers

Pipelines can add third-party code reviewers as quality gates. CodeRabbit and Greptile need their own API keys in Provider credentials. Codex review reuses the machine’s Codex sign-in.

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Choosing a runtime

The choice usually comes down to the model you want and the accounts you already have. You aren’t locked in: a session remembers its runtime and machine between messages, and you can switch either one before any message. The new runtime gets the session’s history. To move a session to a different machine, pick the machine in the agent picker, or pass --machine to kana conv send. See Sessions that move.