Droid 1.0 lets models run hundreds of tool calls in a single request via programmatic tool useA model's ability to call external functions — run code, search the web, edit files — instead of only generating text.Full definition →, and claims up to 20% better efficiency than native model harnesses. Useful for anyone choosing or building an agent harness.
Key takeaways · AI-distilled
Factory reports Script mode, where the model writes sandboxAn isolated environment where AI-generated code or agent actions run without being able to touch anything real.Full definition → JavaScript that runs many tool calls in one request, cut Droid's cost by 15% on Opus 5.5, with savings concentrated in the 12.5% of Scripts making six or more tool calls.
In one Factory session, a Script moved and verified 151 Linear issues with 312 tool calls in 2 model requests and about 61,000 tokens; Factory estimates direct calls would have taken 36 requests and about 3.1 million input tokens.
Droid now appends newly discovered MCP and connector tools to the end of each request instead of the top-of-request tool list, so loading a tool no longer invalidates the cached prefix; Factory says the typical request reads 98% of input from cache.
Numbering every line of file reads cut Opus's cost 22% on one task but raised cost 8% on GLM and 32% on Kimi, so Factory shipped it as an option the model requests, an example of testing each agent harnessThe scaffolding around a model that turns it into a working agent — the loop, the tools it can call, and the rules for when to stop.Full definition → change across model families.
Droid's base prompt fell 37%, from 20,887 to 13,055 tokens, mainly by sending 2 tool definitions up front instead of 11 and loading rarely used tools on demand, even as the system promptThe standing instructions a model receives before any user input — defining its role, rules, tools, and tone for the whole conversation.Full definition → itself grew by about a third.
Terms in this piece · Glossary
agent harness — The scaffolding around a model that turns it into a working agent — the loop, the tools it can call, and the rules for when to stop.
tool use — A model's ability to call external functions — run code, search the web, edit files — instead of only generating text.
sandbox — An isolated environment where AI-generated code or agent actions run without being able to touch anything real.
system prompt — The standing instructions a model receives before any user input — defining its role, rules, tools, and tone for the whole conversation.
