Spawn Agent

An npm package that makes any locally-installed coding agent a Vercel AI SDK provider — spawnAgent("claude") drops Claude Code, Codex, Cursor, Copilot CLI, Gemini, OpenCode, Factory Droid, or Pi straight into streamText/generateText, streamed over the Agent Client Protocol (ACP). One package, eight agents, one API surface. Source: millionco/spawn-agent, https://github.com/millionco/spawn-agent, 2026-06-12

By Aiden Bai (@aidenybai, Million.co — also Security and Review Skills and react-scan). The problem it removes: every time you want to drive claude or codex programmatically you otherwise hand-roll subprocess management and per-CLI stream parsing. spawn-agent normalizes all of that behind the current AI SDK provider spec (LanguageModelV3, with both doGenerate and doStream), so a local agent slots into any existing AI SDK workflow. Source: codeline.co repo review, 2026-04

Usage

import { streamText } from "ai";
import { spawnAgent } from "spawn-agent";   // npm install spawn-agent ai

const { textStream } = streamText({
  model: spawnAgent("claude"),
  prompt: "Refactor src/auth.ts to use the new session API",
});

Pass settings inline or pre-build a provider with createSpawnAgent; use createSpawnAgentSession for stateful multi-turn sessions that keep the agent's memory across calls. Options include cwd, permission (e.g. auto-allow), mcpServers, additionalDirectories, systemPrompt, and inactivityTimeoutMs. Source: millionco/spawn-agent README, 2026-06-12

Supported agents

Custom ACP subprocesses integrate via spawnAgent.fromAdapter(...). Source: GeekNews/AIsle summary, 2026

How it compares

spawn-agent and Vercel's HarnessAgent are the two answers to the same question — embed coding agents in app code without re-implementing each CLI — one via the open Agent Client Protocol, the other as a Vercel-blessed adapter. Both are the application-layer complement to Harness Engineering's "harness portability": write the integration once, swap the harness as the ecosystem moves. spawn-agent shipped v0.0.1 on 2026-04-26 with 26 test files. Source: codeline.co, 2026-04

Source snapshot

Deep review on 2026-07-03 confirmed the local screenshot shows the exact AI SDK surface: spawnAgent("claude") passed into streamText, then async chunks written from textStream. Current public source is still the first npm release:

• npm spawn-agent@0.0.1, MIT, published 2026-04-26.
• Repo millionco/spawn-agent, HEAD f0769c6209876059ec524b436ba606710ee9df6f, no tags returned by git ls-remote.
• GitHub metadata: 167 stars, 9 forks, default branch main.
• ACP adapters checked: @agentclientprotocol/claude-agent-acp@0.55.0; @zed-industries/codex-acp@0.16.0.

This remains a candidate integration primitive rather than an installed default. Use it when an app needs to call local coding agents through the AI SDK; for ordinary Codex/Claude workflows, use the harness directly.

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Timeline

• 2026-07-03 | Deep-reviewed the local launch screenshot and refreshed npm/GitHub/ACP package snapshots. Source: X/@aidenybai, 2026-04-29; Source: npm/GitHub, 2026-07-03
• 2026-04-29 | @aidenybai introduced spawn-agent ("an API call any coding agent on your machine, works w/ claude code, codex, cursor, opencode, pi… npm install spawn-agent"). 407 likes, 269 bookmarks. Source: X/@aidenybai, 2026-04-29
• 2026-04-26 | v0.0.1 published (millionco/spawn-agent, MIT, TypeScript) — Vercel AI SDK provider for 8 coding agents over the Agent Client Protocol. Source: millionco/spawn-agent, 2026-06-12
• 2026-06-12 | Page created from coding-agents bookmark absorption; verified against the GitHub repo and AI SDK provider spec. Source: millionco/spawn-agent, 2026-06-12