The authors introduce Harness Continual Learning (HCL), a paradigm where an agent improves by evolving its execution-facing harness rather than updating model parameters. This approach addresses the challenge of retaining previously acquired behavior while adapting to new experiences through components like prompts, memories, and routing rules.

  • HCL utilizes four components: Task Interface, Experience Memory, Capability Map, and Adaptive Router.
  • Guarded harness evolution separates update generation from state commitment using a Continual Optimizer and Evaluator.
  • Experiments show relative gains exceeding 10% over baselines in textual reasoning, multimodal perception, and open-world interaction.
  • Controlled retention sweeps reveal measurable harness-level forgetting and allow explicit adjustment of the stability-plasticity trade-off.

This method enables capability accumulation and failure recovery without disrupting behavior acquired earlier by keeping the foundation model frozen.