Arcee AI said on August 13, 2026 that its Open Models API beta now includes frontier open models from other developers alongside its own Trinity family. Developers can choose among several model families through one service, which gives them alternatives for demanding, long-running AI agentAn AI system that doesn't just answer once but works toward a goal in a loop — taking actions, reading the results, and deciding what to do next.Full definition → tasks.
The announcement came with the open-sourcing of nac, Arcee's internal 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 →, the software that runs an agent through extended tasks. Arcee says the broader catalog will show which models users choose for which tasks, and why, and that experience with nac will inform how its API routes, serves and supports models for long-running work. Those are stated development plans. The immediate change is the wider selection.
Terms in this piece · Glossary
AI agent — An AI system that doesn't just answer once but works toward a goal in a loop — taking actions, reading the results, and deciding what to do next.
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.
token — The chunk of text a model reads and writes in — roughly three-quarters of a word — and the unit AI usage is billed in.
