SYNTHESIS NOTE
Recommender Systems

Can users steer recommendations with natural language at inference?

Can recommendation systems let users specify their preferences in natural language at inference time without retraining? This matters because it would let new users and existing users dynamically adjust what they want to see.

Synthesis note · 2026-05-03 · sourced from Recommenders Personalized
How do recommendation feeds shape what people see and believe? What breaks when specialized AI models reach real users?

Sequential recommenders predict a user's next interaction from history. Recent work uses LLMs to extract preferences from reviews and feed them as auxiliary supervision during training, but this approach can't be steered at inference: the user's preferences are baked into the model weights, so a new user requires fine-tuning to be served well.

Preference discerning is a different paradigm. Instead of training the model to embody preferences, it conditions the generative recommender on user preferences as text in the model's context window at inference time. An LLM extracts preferences from user reviews and item-specific data, producing a textual description of what the user wants. This text is fed into the sequential recommender as in-context conditioning, alongside the interaction history.

The architectural shift unlocks several capabilities. Users can specify in natural language what they want or want to avoid ("more action, less romantic"). New users without retraining can be served by computing their preferences from minimal data and injecting them into context. The system can be evaluated on preference-following capability, not just next-item prediction — Mender's benchmark covers preference-based recommendation, sentiment following, fine-grained steering, coarse-grained steering, and history consolidation. State-of-the-art sequential recommenders fail several of these axes because they don't have a mechanism to incorporate preferences they didn't train on; Mender succeeds because preferences are a runtime input, not a training target.

The general lesson: making something a context input rather than a parameter target trades efficiency (longer prompts) for flexibility (runtime steering). For tasks where users know better than the training set what they want, the trade is worth it.

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Original note title

preference discerning conditions sequential recommenders on natural-language preferences in context — letting users steer at inference without fine-tuning