Antigravity ACP Server

An Agent Client Protocol (ACP) server for Google Antigravity's agy CLI, built on Bun. It lets any ACP-compatible editor drive agy: it spawns the CLI, streams its progress live, and replays conversation history on demand.

⚠️ Terms of Service risk

Google's Antigravity Terms of Service state:

You must not abuse, harm, interfere with, or disrupt the Service. This includes, but is not limited to, using the Service in connection with products not provided by us. Using third party software, tools, or services to access the Service (e.g. using OpenClaw with Antigravity OAuth) is a breach of this Agreement. Such actions may be grounds for suspension or termination of your account.

antigravity-acp does not itself request, store, or process any authentication credentials — it only spawns the official agy binary as a subprocess and talks to it over stdio; all Google OAuth login is handled entirely by agy itself, outside of this project. However, the effect is still a non-Google, ACP-compatible editor driving agy (and therefore your Antigravity account) through a third-party tool — the exact pattern Google's FAQ names as a Terms of Service violation (Claude Code, OpenClaw, OpenCode, and by extension this project).

By using antigravity-acp with an agy session logged into your personal Antigravity account, you accept the risk that Google may suspend or terminate that account. This project is provided as-is, with no warranty, and its authors and contributors accept no liability for any account action Google takes as a result of its use. If you want to avoid this risk entirely, Google recommends authenticating with a Vertex AI or AI Studio API key instead of an Antigravity OAuth login.

See #3 for background.

Run

From source (Bun required):

bun run index.ts          # ACP over stdio
bun run index.ts --version

As a compiled single-executable (no Bun required):

dist/agy-acp-darwin-arm64   # macOS Apple Silicon
dist/agy-acp-darwin-x64     # macOS Intel
dist/agy-acp-linux-arm64    # Linux ARM64
dist/agy-acp-linux-x64      # Linux x86-64
dist/agy-acp-windows-arm64.exe # Windows ARM64
dist/agy-acp-windows-x64.exe   # Windows x86-64

Both modes speak ACP over stdio — point your editor at the binary as-is.

agy auto-install

The server locates agy at startup using this priority order:

1. An agy binary placed next to the executable (dist/agy, or bin/agy when running from source after bun install).
2. $AGY_BIN — set this to point at your own build.
3. agy on $PATH.

If none are found the server downloads the matching release from GitHub (google-antigravity/antigravity-cli) and verifies its SHA-256. The download is skipped when AGY_SKIP_DOWNLOAD=1 or $AGY_BIN is set.

bun install runs the same download via the postinstall hook, so a plain bun install also provisions agy for source runs.

Flags / env

AGY_BIN	Path to an agy binary; skips the auto-download
AGY_SKIP_DOWNLOAD	Set to 1 to skip the download entirely
AGY_EXTRA_ARGS	Extra args forwarded to every agy invocation
AGY_CONVERSATIONS_DIR	Custom directory where agy writes its conversation SQLite databases

Build (Single Executable Application)

bun run build:mac-arm64    # → dist/agy-acp-darwin-arm64
bun run build:mac-x64      # → dist/agy-acp-darwin-x64
bun run build:linux-arm64  # → dist/agy-acp-linux-arm64
bun run build:linux-x64    # → dist/agy-acp-linux-x64
bun run build:win-arm64    # → dist/agy-acp-windows-arm64.exe
bun run build:win-x64      # → dist/agy-acp-windows-x64.exe
bun run build:all          # all six at once

The compiled binary embeds the entire TypeScript source and all dependencies. It auto-downloads agy on first launch if not present next to the executable.

ACP surface

• initialize — advertises loadSession, additionalDirectories, list/delete/resume/close, embeddedContext.
• session/new — accepts cwd and additionalDirectories; returns the session configuration options (including modes and available models).
• session/set_config_option — model and mode selection; persisted per session.
• session/load — replays full conversation history from the agy SQLite DB, including tool calls, task/permission/error decorators, and title updates.
• session/resume — re-attaches a client and re-sends available_commands_update and config_option_update notifications.
• Post-session notifications — after every session/new, session/load, and session/resume the server sends available_commands_update → config_option_update in order, so the UI can render the mode picker and model selector immediately.

Architecture

index.ts                      entry: startup, agy auto-install, ACP wiring
src/
  acp/                        ACP surface
    server.ts                 Bun stdio <-> ndJsonStream <-> agent
    agent.ts                  initialize / session.* / prompt / cancel
    sessions.ts               in-memory registry + eviction
    adapter.ts                prompt turn: spawn agy, poll, stream
    client.ts                 AgentContext wrapper (notify / request)
  agy/
    binary.ts                 resolve binary: SEA-local / bin/ / $AGY_BIN / PATH
    installer.ts              shared download + SHA-256 verify + extract logic
    process.ts                Bun.spawn, arg building, model discovery
  constants/
    index.ts                  shared constants (paths, poll intervals, modes, commands)
  conversation/
    database.ts               bun:sqlite reader (reusable handle)
    scan.ts                   discover new conversation DBs
    translator.ts             shared step -> ACP engine (stream + replay)
    streaming.ts              live poll loop (stream mode)
    replay.ts                 history replay + incremental cache
    columns.ts                error / permission / task decoders
    updates.ts                per-step dispatcher
  updates/                    per-tool ACP builders + shared utils
  store/sessionStore.ts       persistent session bindings (atomic, serialized writes)
  narration/                  narration filter
  gen/steps.ts                generated protobuf
  types/                      type definitions (session, step row)
  utils/lru.ts                small LRU
scripts/
  postinstall.ts              npm install hook: download agy into bin/

Shared streaming/replay engine

Live streaming and history replay differ only in how they treat the agent's growing text stream. Everything else — tool calls, titles, user prompts, and the task/permission/error enrichment — is identical, so both drive a single Translator:

• stream emits the newly-appended text slice each poll and dedups tool steps it has already sent;
• replay buffers consecutive agent-text parts and flushes them as one message at each boundary.

Caching & performance

• Incremental replay cache (replay.ts): replays are cached per conversation and validated by file (mtime, size). An unchanged conversation returns instantly; a conversation that merely grew has only its new tail of steps read and translated, then appended. (agy DBs are append-only.)
• Reused DB handle: the live poll loop keeps one bun:sqlite handle + prepared statement open for the whole turn instead of reopening each tick.
• Bun-native throughout: bun:sqlite, Bun.spawn, Bun.stdin/Bun.stdout, Bun.file/Bun.write — no better-sqlite3, protobufjs runtime, or node-stream shims.

Test

bun run typecheck
bun test