Harnesses & personalities
Two more concepts shape how a session behaves: the harness and the personality.
Harness
Section titled “Harness”The harness is the coding agent running inside the session VM — Claude
Code, Codex, Gemini, or a custom agent. Your fleet sets a default harness and
model; a session can switch mid-thread with the !provider and !model
commands (see the Slack guide).
The harness is orthogonal to the compute provider: choosing Claude Code does not decide whether you run on Sprites or Modal.
Personality (skillset)
Section titled “Personality (skillset)”A personality is the skillset applied to a session when it
is provisioned — the prompts, rules, and configuration that shape how the
agent works. Your fleet has a default personality; individual sessions can
override it (name a skillset when starting the session, or switch mid-thread
with !skillsets switch), and triggers can set
their own.
Personalities are where Sessions and the open-source Skillsets project meet: the same skillset format that improves a local agent also configures a managed session.
Next steps
Section titled “Next steps”- Integrations & credentials — connect the agent providers each harness needs.
- Slack guide — switching harness, model, and skillset from a thread.
- Skillsets — the open-source project behind personalities.
this page as markdown: /sessions/concepts/harnesses-and-personalities.md· index for agents: /llms.txt