Large Language Models (LLMs) are becoming widely used to support various workflows across different disciplines, yet their potential in discrete choice modelling remains relatively unexplored. This work examines the potential of LLMs as assistive agents in the specification and, where technically feasible, estimation of Multinomial Logit models. We implement a systematic experimental framework involving twelve versions of seven leading LLMs (ChatGPT, Claude, DeepSeek, Gemini, Gemma, Llama, and Mistral) evaluated under five experimental configurations. These configurations vary along three dimensions: (i) modelling goal (suggesting vs. suggesting and estimating MNL models); (ii) prompting strategy (Zero-Shot vs. Chain-of-Thoughts (CoT)); and (iii) information availability (full dataset vs. data dictionary summarising variable names and types). Each specification suggested by the LLMs is implemented, estimated, and evaluated based on goodness-of-fit metrics, behavioural plausibility, and model complexity. Our findings reveal that proprietary LLMs can generate valid and behaviourally sound utility specifications, particularly when guided by structured prompts (CoT). Open-weight models such as Llama and Gemma struggled to produce meaningful specifications. Notably, some LLMs performed better when provided with just data dictionary, suggesting that limiting raw data access may enhance internal reasoning capabilities. Among all LLMs, GPT o3, operating in an agentic setting, was uniquely capable of correctly estimating its own specifications by executing self-generated code. Overall, the results demonstrate both the promise and current limitations of LLMs as assistive agents in discrete choice modelling, not only for model specification but also for supporting modelling decision and estimation, and provide practical guidance for integrating these tools into choice modellers’ workflows.

Discrete choice analysis aims to understand and predict decision-makers’ behaviour, a goal that is crucial across several disciplines, including transportation. This type of analysis has relied predominantly on static representations of preferences, principally through the Random Utility Maximisation (RUM) model, due to its ease of implementation, economic interpretability, and statistical formality. However, this model assumes that individuals possess complete information about all attributes of alternatives and that they can process and recall this information instantaneously, which may not align with actual human behaviour. In contrast, the Decision Field Theory (DFT) model from mathematical psychology explicitly incorporates the repeated scrutiny of attributes and recall effects within the decision-making process, which enables it to model attention weights, but lacks microeconomic interpretability and clear statistical parameter identification. This paper introduces the RUM-DFT model, which seeks to integrate strengths of both approaches. Through Monte Carlo simulations, the proposed model is shown to be able to: (i) recover parameters related to the deliberation process, (ii) replicate the dynamic behaviour of utilities during deliberation as observed in practice, (iii) maintain economic interpretability by estimating coefficients that can be used to calculate the marginal indirect utilities, and (iv) highlight the pitfalls of using a RUM model that disregards the true dynamics of data generation process. The SwissMetro case study is employed also to evaluate the RUM-DFT model using a real-world dataset, demonstrating the viability and superior goodness-of-fit of the proposed model.