Trading with Memory: How Accumulated Experience Shapes LLM Trading Behavior

Powerful LLM agents are increasingly used for complex decision-making, but trading poses a distinctive challenge: decisions unfold over long histories, while noisy market data make it difficult to know what past information should matter. We ask: when an LLM trading agent takes over a portfolio, what does it inherit? It inherits a way of seeing the portfolio, not just the portfolio itself. Our experiments show that the same portfolio, exposed to the same future market, can lead to different trading decisions depending on the agent’s history. Agents that retain their experience trade 47% less than those starting with a blank history, with 81% of the difference emerging in the first continuation session. The key is not simply remembering what happened. Agents trade even less when they retain their previous investment judgments, suggesting that they carry forward their own beliefs about why positions should be held. This behavioral continuity persists over much longer histories and subsequent trading periods. These findings suggest that experience changes more than what an LLM trading agent knows. It changes how the agent interprets what it currently holds—and therefore what it does next.