UniiChat

▶ Watch the announcement video

This repo is vibe-coded. AI agents wrote nearly all of it, and AI agents reviewed it. Read it, run it and fork it as such: expect bugs.

UniiChat is an AI agent with one chat that never ends. There is no "new chat" button: you talk to the same agent for days, weeks, years, and it remembers. The hosted version is at https://uniichat.com. This is its source, to run your own server on your own API keys.

How it works

• One chat, a memory tree. Every message is summarized into one line, and neighboring lines are merged in pairs, again and again, into a binary tree. Each call sees a view of the whole chat, up to 128 KB: recent messages one line each, older ones covered by fewer, broader lines. Detail fades with age, but nothing is lost.
• Zoom. The agent can open any line into the two it was made from, down to the original message. So its context never rots, and it never needs a "compaction" that throws the past away.
• Built in the background. Summaries are written by a cheaper model (the compactor) as messages arrive. The view changes only at its end, so each call reads most of its input from the vendor's prompt cache.
• Every window is a view. The server owns the chat. A browser tab, or unii in a terminal, shows it live; any of them can send a message, stop the work, or change the model.
• Agents and tools. The agent runs a shell, reads and edits files, and can drive a Mac's screen, on any computer where unii is open (each is a device it can name). It can spawn subagents, which work in the background and report back as messages.
• Import. Bring your past Claude and ChatGPT chats (Claude Code and Codex folders, or the websites' exports); they join the tree.

The design is in the header comment of each file. Start with Memory.ts (the tree and the view), Server.ts (the chat, turns, workers) and AskAI.ts (model calls and the cache).

Run it

You need Bun and an Anthropic API key (or an OpenAI one, below).

export ANTHROPIC_API_KEY=sk-ant-...
bun Server.ts                    # http://127.0.0.1:8788, data in ~/.unii

Then open http://127.0.0.1:8788 and type your email. With no mail key set, the server prints the sign-in link in its output: open it. Or chat from a terminal:

bun Term.ts http://127.0.0.1:8788

It asks for your email, the server prints a link, and the page it opens asks for the code the terminal shows. bun Term.ts help lists the rest.

Other commands:

bun run test                     # the tests, each file on its own
bun run web                      # rebuilds web/app.js from web/src
bun build --compile Term.ts --outfile unii
                                 # one `unii` executable; `unii serve`
                                 # runs the server it carries

Your chats live in ~/.unii/users/, one JSON line per message (main/) and per summary (tree/). They are the memory: back them up.

Config

~/.unii/config.json (optional; the dir is $UNII_DIR). Each key may also be set as the variable UNII_<KEY>:

• site: the server's origin, for sign-in links (default http://127.0.0.1:8788). Another port: UNII_SITE=http://127.0.0.1:9000 bun Server.ts 9000.
• vendors: what the server offers, comma-separated: claude-api (default), openai-api.
• models: the models offered, by label (Pick.ts; default all).
• pick: what a chat runs on until it picks another, vendor:model:effort:speed (default claude-api:sonnet-5.5:medium:slow).
• compactor: what writes the summaries (default claude-api:haiku-5.5:high:slow).
• agents: what subagents run on (default: the chat's pick).
• work: the agents' working dirs on each device (default ~/.unii/work).
• rules: a file appended to every system prompt.
• after: a shell command run after each turn.
• workers: how many processes serve the users (default none: one process). With a number, Server.ts only routes, behind a proxy that honors its x-unii-worker header (Server.ts explains).
• apple, apns: the iOS app's App ID and push key id (ios/).

Keys are read from the environment: ANTHROPIC_API_KEY, OPENAI_API_KEY, RESEND_API_KEY (to email sign-in links; none: they print), APNS_KEY.

With only an OpenAI key, set vendors, pick and compactor to openai-api models, e.g. UNII_VENDORS=openai-api UNII_PICK=openai-api:gpt-6.1-sol:medium:slow UNII_COMPACTOR=openai-api:gpt-6-luna:high:slow.

A self-hosted server is free: it bills no one, shows no prices, and calls only the model vendors. Billing.ts is the one place a hosted server plugs in its billing (uniichat.com sells credits; this repo has none).

The unii terminal

web/install.sh (served at /install.sh) runs the official installer, which installs the released unii executable. unii alone opens uniichat.com; unii <url> opens any server. Run with UNII_COMPUTER=1 on a Mac, the agent may use its screen (it compiles Computer.swift with swiftc; macOS asks for Screen Recording and Accessibility).

Telemetry: once a day the unii terminal asks bend-lang.com's /check for the latest version (Term.ts update_check), sending its version, OS and CPU type, no account and no id; it also says whether this computer has ever self-hosted (set for good the first time it runs unii serve or opens a server other than uniichat.com). It is the one call a self-hosted UniiChat makes to us. UNII_NO_TELEMETRY=1 turns it off.

License

Apache-2.0 (LICENSE). Copyright 2026 Higher Order Company.