# Built-in harnesses reorganized as a tree by use case

> Base, Conversation, Worker, Bashkit Worker and Sandbox Worker now form a tree of built-in harnesses, and existing Worker bindings move by sandbox policy.

Source: <https://everruns.com/docs/changelog/2026-10-10-harness-tree/>

Date: 2026-10-10
Products: Platform, Cloud
Category: Improvement
Pull request: everruns/everruns#4484

The built-in harnesses now form a tree where each layer answers one question. **Base** carries the system essentials. **Conversation** (the default) adds chat features with no workspace, and **Worker** adds files, skills and delegation with no compute. **Bashkit Worker** and the new **Sandbox Worker** split Worker by where commands run, and each enforces that rule on agents and sessions.

Organizations are migrated once: agents bound to the old Worker move to Bashkit Worker or Sandbox Worker based on their sandbox policy. Worker Base and Generic stay as deprecated harnesses for existing bindings.

See [Built-in harnesses](https://everruns.com/docs/features/harnesses/#built-in-harnesses) and [#4484](https://github.com/everruns/everruns/pull/4484).