Earendil Works
Boutique lab crafting tools to harness AI — Pi and Lefos.
Earendil Works 'crafts tools to harness AI': Pi, the minimal, steerable agent toolkit (unified LLM API, agent loop, TUI) that became a favorite base for custom harnesses, and Lefos. Built in the open, shaped by the humans who use them.
Open-source project
In the news
DeepSeek ships Harness Desktop; the 'everything is a plugin' harness passes 240k stars
DeepSeek releases a macOS and Windows Desktop app for DeepSeek Harness, its open-source agent harness where everything — tools, sub-agents, even the loop — is a plugin. The repo passed 240k stars within three months of its August launch, making it the fastest-growing harness in the field's history.
xAI open-sources Grok Build, its coding agent harness
xAI open-sources Grok Build — a Rust coding agent harness and fullscreen TUI around Grok models — unusually early for a first-party tool. It joins Claude Code, Codex and Gemini CLI as the fourth major first-party harness, now with a fourth open one.
Anthropic launches the Claude Agent SDK
Anthropic open-sources the SDK behind Claude Code — the agent loop, tool use, subagents, memory and hooks — letting developers build their own Claude-powered agents on production rails.
Browser Use tops 50k stars — web agents go mainstream
The open-source library for letting agents drive browsers becomes one of the fastest-growing repos in AI, spawning hosted products and a wave of 'web operator' agents.
Related startups
LangChain
The de-facto standard toolkit for building LLM applications and agents.
LangChain makes the LangChain framework and LangGraph, the low-level orchestration standard for stateful, controllable agents, plus the LangSmith platform for tracing, evaluating and monitoring them in production.
Cognition
Devin, the AI software engineer, and the Windsurf IDE.
Cognition builds Devin, an autonomous AI software engineer that plans and executes engineering tasks end-to-end, and acquired the Windsurf agentic IDE in 2025. One of the defining startups of the coding-agent wave.
Sierra
Conversational AI agents for customer experience.
Sierra, co-founded by Bret Taylor and Clay Bavor, builds production conversational agents that resolve real customer issues with guardrails, evaluation and human escalation — a template for deploying vertical agents at the enterprise edge.