Best Of Agent Harnesses

From the release notes

What's new Three harnesses from the YC Paper Club talk are in. Prime Agent (Prime Intellect, 95.5% on ARC-AGI-3 with Opus 5), QM (Y Combinator's multiplayer harness for work), and OpenJarvis (Stanford's local-first stack). 167 harnesses, stars captured 2026-09-13. Three new decision guides (16 total). Why the harness matters more than the model: the measurements (ARC-AGI-3 30% to 95.5% on the same weights, SWE-bench Pro 23% to 52%, Cursor 46% to 80%, Harness-Bench rank correlation -0.05), a table of twenty labs, papers, and practitioners with checked links, and what the claim does not mean, from the YC Paper Club session of September 7. Managed vs self-hosted always-on agents: Grok Bot, Claude Managed Agents, QM, OpenClaw, Hermes, OpenJarvis. Who owns the computer, who pays for idle time. The best AI agent harnesses in 2026, ranked by category: the top three per category from the live data, regenerated on every weekly refresh. README and machine-readable surfaces. The intro now carries the long-horizon numbers, the two eras of harnesses, and the pairing rule. Two new FAQ entries (the thesis, Grok Bot) flow to the README, llms.txt, harnesses.json, and the site's FAQPage. llms.txt states the thesis in its blurb; the site adds llms-full.txt (llms.txt plus every guide). Site. Every guide page carries TechArticle JSON-LD with real published and modified dates, breadcrumbs on all project, category, and guide pages, and a per-URL sitemap date. Guide links now resolve on the site (they previously pointed at .md paths that 404 under /compare/). MCP. compare prefers a guide that names the compared projects in its title. The 0.5.2 package on PyPI already serves the new projects and guides from main; the tie-break ships in the next package release.

From the release notes

What changed since August 12 MCP server works again. agent-harnesses-mcp 0.5.2 pins the MCP SDK below 2.0. The 2.0 release (July 28) renamed FastMCP, and 0.5.1 crashed on startup for anyone who installed it. Install: claude mcp add agent-harnesses -- uvx agent-harnesses-mcp. Cold-tested: initialize and tools/list complete, 10 tools. 164 harnesses, 12 categories. New in the tables: YYLO (coding agent products), AnythingLLM (personal agent runtimes), ClawBench (evaluation and benchmarking). Flowise stays listed with its archived flag instead of moving to the Graveyard. Roo Code is out of the turnkey coding agent pick and stays in the tables with its archived flag. On the radar. DeepSeek Harness (pinned, not ranked, pending a star-velocity check on 2026-10-07), Google Antigravity SDK, L∞pGate, and eight community submissions below the ranked-table bar. Community submissions now reach the curation queue. Open "Add project" issues feed the weekly discovery run, so the biweekly curation pass vets them with live repo data and closes the issue when an entry lands. Site. The nav shows a live star count that links back to the repo. Weekly rescores on August 16, 23, 30, September 6 and 9 refreshed every star count and the landscape charts. Thanks to contributors HelpMatey (#61), InsightFactoryAPP (#111), reacher-z (#60), rxdt (#69), and danawoodman (#78).

From the release notes

agent-harnesses-mcp 0.5.2: pin the mcp SDK below 2 so the server star…