Nexa: A Native Domain-Specific Language and Virtual Machine for Agentic Workflows

Executing non-deterministic, I/O-bound agentic workflows atop general-purpose languages like Python introduces impedance mismatches: fragile state management, runtime overhead, and complex fallback handling. We present Nexa, a DSL and VM co-designed for agentic computing. TheNexa DSL elevates prompts, agents, and tool calls to first-class primitives with declarative control flow. The Nexa VM employs an Actor model for concurrent execution and an immutable tree-based state engine with Copy-on-Write semantics, enabling O(1) logical state snapshotting with sub-millisecond overhead. Evaluation on WebArena and SWE-bench demonstrates clearer semantic expression and competitive performance. Ablation studies confirm each mechanism’s contribution. Nexa bridges language abstraction and execution efficiency for next-generation LLM applications.