Using GPT-4.1, an older, non-reasoning model, a basic customer-service agent reaches 67.5% Pass^4 on τ²-bench retail — meaning it solves the task on all four independent attempts for 67.5% of tasks. It scores above every retail entry in our October 12, 2026 leaderboard snapshot. It runs on the benchmark's stock ReAct scaffold, with learned guidelines appended to its system prompt.

ALTK-Evolve builds that playbook using GPT-4.1. It analyzes the agent's training-task attempts and uses the model to distill successes and failures into short behavioral rules: how to authenticate a customer, confirm a transaction, or handle a return. Those guidelines are then added to the agent's prompt for subsequent conversations. The same model powers both guideline extraction and the agent; no weight updates or human annotation are needed.

Our previous work demonstrated this approach on coding agents. Here, we test it on customer service, where success requires following domain policies, understanding a customer's request, and executing the right tool actions.

τ²-bench (from Sierra) measures how well an agent handles customer-service conversations under real constraints. Each task pairs the agent with an LLM-simulated customer who has a goal in mind, a set of domain tools (look up an order, issue a refund, rebook a flight), and a written policy document the agent must follow. The agent has to draw out the right details, stay within policy, and take the correct — often irreversible — actions; a task counts as solved only when the final database state matches the expected outcome, a strict binary reward.

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