Today we're open-sourcing nac, an agent harness for long-running tasks, and launching the Arcee open models API beta.
Nac is available now under Apache 2.0 on GitHub, built for developers running complex, multi-step engineering workloads.
A central orchestrator plans work and dispatches it to isolated worker threads. Workers execute in clean contexts, make their edits, and return a concise summary—an episode.
The worker process exits and its raw context is discarded, while the episode persists.
Threads can weave episodes between each other to share context without carrying historical noise. Nac also ships with an MCP server.
Interactive coding agents like Claude Code or Codex can use nac as a tool, delegating long-running background execution while keeping your interactive chat fast.
To support these workloads, we are expanding our API beyond Trinity with the Arcee open models API beta.
Long-horizon tasks require different model strengths at different steps. Hosting a broader catalog gives you choice, while helping us learn how frontier open models perform in persistent agent runtimes.
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.
context window — The maximum amount of text a model can consider at once — its working memory for the current conversation or task.
MCP — The Model Context Protocol — an open standard that lets any AI assistant plug into any tool or data source without custom integration code.
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.
Why it matters
A concrete answer to context windowThe maximum amount of text a model can consider at once — its working memory for the current conversation or task.Full definition → bloat in long-running agents: isolate workers, discard their transcripts, keep episode summaries. Over MCPThe Model Context Protocol — an open standard that lets any AI assistant plug into any tool or data source without custom integration code.Full definition →, your interactive coding 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 → can hand off background work and stay fast.
