BitFun is a cross-platform desktop agent runtime with a Rust core that gives each task its own interface. Rather than routing every task through one chat box, it generates a Mini App — a chart, a board, a form, a panel — and binds the conversation to that interface's live state, so questions refer to what is on screen instead of re-describing it. Community builds range from market dashboards to domain-specific tools, and a public Mini Apps gallery collects them.
Two kinds of work are in scope. For coding, it plans, edits, tests, debugs, reviews, and commits inside real Git repositories, including long-horizon tasks. For office work, it handles research, writing, presentations, meeting notes, and reports. When a task leaves the editor, the execution layer reaches the browser, the terminal, desktop applications, the filesystem, Computer Use, and remote workspaces.
Customisation runs in four tiers: custom agents defining roles, flows, constraints, and tool bundles; MCP servers, skills, and lifecycle hooks that are compatible with Codex hooks so existing hook scripts run unchanged; Mini Apps for task-specific interfaces; and source-level changes to tools, adapters, UI, or runtime.
Account login, cross-device session and settings sync, and controlling one signed-in device from another all run through a relay you deploy yourself, with no vendor cloud in the path. The relay is described as zero-knowledge: clients derive keys locally and the server holds only Argon2id hashes and AES-GCM-wrapped material.
Published measurements come from initial single-run evaluations on Deepseek-V4-Pro, and are presented as an early signal rather than a fixed ranking: an average KV cache hit rate of 98.67% over a SWE-Bench-Pro round, attributed to byte-stable prompt assembly across turns, and search-time reductions of up to 94.6% (about 36.1x on average) on tens-of-millions-line repositories such as Chromium using a resident cross-turn index called flashgrep.
Features
- Agentic Mini Apps: each task gets a generated interface, with the conversation bound to that interface's live state
- Coding agent: plan, edit, test, debug, review, and commit inside real Git repositories
- Office work: research, writing, presentations, summarisation, meeting notes, and reports
- Desktop execution: browser, terminal, desktop applications, filesystem, Computer Use, and remote workspaces
- Four customisation tiers: custom agents, then MCP/skills/hooks, then Mini Apps, then source-level changes
- Codex-compatible hooks: existing Codex hook scripts run at BitFun lifecycle points unchanged
- Self-hosted device sync: login, cross-device sync, and remote device control through a relay you deploy
- Prompt cache stability: byte-stable prompt assembly across turns, measured at a 98.67% average KV cache hit rate
- flashgrep search: a resident cross-turn index cuts repeated repository search time on very large trees
- Cross-platform and model-agnostic: Windows, macOS, and Linux, with the model configured by you
