# Pact: A Choreographic Language for Agentic Ecosystems

arXiv: https://arxiv.org/abs/2605.03143 · HTML: https://mlsanity.com/paper/2605.03143/

## Key facts

- Cited by 2 papers in the map (data through 14 Oct 2026).
- Placed in Social simulation and multi-agent debate, one of 16 directions in LLM agents and tool use.
- Builds on 7 of its 21 references that are in the map.
- First posted on arXiv 4 May 2026.

## Placed in

- LLM agents and tool use / [Social simulation and multi-agent debate](https://mlsanity.com/agents/social-simulation-and-multi-agent-debate/)

## Builds on (most cited first, 7 of 7)

- [Improving Factuality and Reasoning in Language Models through Multiagent Debate](https://mlsanity.com/paper/2305.14325/) (2023)
- [ChatEval: Towards Better LLM-based Evaluators through Multi-Agent Debate](https://mlsanity.com/paper/2308.07201/) (2023)
- [HasChor: Functional Choreographic Programming for All (Functional Pearl)](https://mlsanity.com/paper/2303.00924/) (2023)
- [Efficient, Portable, Census-Polymorphic Choreographic Programming](https://mlsanity.com/paper/2412.02107/) (2024)
- [Cutting the Cake: A Language for Fair Division](https://mlsanity.com/paper/2304.04642/) (2023)
- [HasTEE+ : Confidential Cloud Computing and Analytics with Haskell](https://mlsanity.com/paper/2401.08901/) (2024)
- [Toward Verified Library-Level Choreographic Programming with Algebraic Effects](https://mlsanity.com/paper/2407.06509/) (2024)

## Built on by (most cited first, 2 of 2)

- [Causal Past Logic for Runtime Verification of Distributed LLM Agent Workflows](https://mlsanity.com/paper/2605.20923/) (2026)
- [Evaluating Rational Contracting in Natural Language](https://mlsanity.com/paper/2608.10475/) (2026)

## Abstract (arXiv)

Recent advances in large language models have led to the rise of software systems (i.e. agents) that execute with increasing autonomy on behalf of users in open, multi-party settings, interacting with untrusted counterparts and managing private information. Choreographic programming offers correct-by-construction protocol-design for such settings, but assumes cooperative participants -- it has no notion of agent self-interest, that is, why an agent will follow a protocol. In this talk we introduce Pact, a choreographic language extended with operations to describe agent choices and preferences, drawing from the rich literature of game theory. Every Pact protocol maps to a formal game, allowing protocol designers to reason about game-theoretic properties of their protocols, such as solving for decision policies. We present Pact's design and a preliminary implementation -- a bounded-rational solver that computes decision policies over Pact protocols -- and findings from applying this language to multi-party coordination with self-interested agentic participants.