WebExplorer: Explore and Evolve for Training Long-Horizon Web Agents
Junteng Liu et al.
arXiv:2509.06501
In short
Web agents are held back by a lack of hard training questions. WebExplorer generates them by exploring the web and evolving questions to be harder, then trains an 8B agent with SFT and RL that searches over about 16 turns and beats much larger agents.
Why it matters
Hard synthetic data, not model size, turns out to be the lever for web agents.
Read first
The 3 Field Guide ideas this paper leans on.
Starting from scratch? The full route 23 ideas · basics first
- Dataset ✓ understood
A collection of data examples used for training, validating, or testing machine learning models.
- Synthetic Data · read first ✓ understood
Artificially generated data created to augment training sets, protect privacy, or simulate rare scenarios.
- Machine Learning ✓ understood
Building systems that learn patterns from data instead of following hand-written rules, getting better at a task as they see more examples.
- Reinforcement Learning · read first ✓ understood
Learning through interaction with an environment, receiving rewards or penalties to learn optimal behavior policies.
- Natural Language Processing ✓ understood
The field of AI that lets computers read, interpret, translate and generate human language, from spam filters and search to chatbots.
- Token ✓ understood
The basic unit of text that a language model processes, typically representing a word, subword, or character. Tokens are the fundamental building blocks for LLM input and output.
- Tokenization ✓ understood
Splitting text into tokens, usually subword pieces, and mapping each to an integer ID so a language model can process it.
- Language Modeling ✓ understood
Learning probability distributions over sequences of words to predict what comes next.
- Training ✓ understood
The process of fitting a model to data by repeatedly measuring how wrong its outputs are and adjusting its parameters to reduce that error.
- Unsupervised Learning ✓ understood
Learning from unlabeled data to discover hidden patterns, structures, or relationships without explicit target outputs.
- Self-Supervised Learning ✓ understood
Learning representations from unlabeled data by creating supervised tasks from the data itself (masked prediction, contrastive learning).
- Pre-training ✓ understood
Training a model on a large dataset (often self-supervised) before fine-tuning on specific tasks, enabling transfer learning.
- Feature ✓ understood
A single measurable property of an example, such as a house's floor area or how many links an email contains, used as an input to a model.
- Neural Network ✓ understood
A computational model inspired by biological neural networks, consisting of interconnected nodes (neurons) organized in layers that process information through weighted connections.
- Deep Learning ✓ understood
A subset of machine learning that uses neural networks with multiple layers (deep neural networks) to learn hierarchical representations of data.
- Representation Learning ✓ understood
Learning useful features or representations of data automatically, rather than hand-crafting them.
- Embedding ✓ understood
A list of numbers (a vector) that represents a word, sentence, image or other item, learned so that similar items end up close together.
- Attention Mechanism ✓ understood
A technique that lets a neural network weigh every part of its input when producing each output, focusing on the parts most relevant at that step.
- Transformer ✓ understood
A neural network architecture, introduced in 2017, built from stacked self-attention and feed-forward layers; the basis of nearly every modern large language model.
- Large Language Model ✓ understood
A neural network, almost always a transformer, trained on vast amounts of text to predict the next token, which lets it write, answer, summarize and follow instructions.
- Context Window ✓ understood
The maximum number of tokens an LLM can process at once, including both input prompt and generated output. Also called context length.
- Tool Use ✓ understood
LLMs learning to call external tools, APIs, or functions to extend capabilities beyond text generation (calculators, search, code execution).
- AI Agent · read first ✓ understood
A system where a large language model decides its own next steps in a loop: calling tools, reading the results, and continuing until the task is done.
In the frontier
- Rank
- #75 of 100
- Citations
- 74
- as of Aug 9, 2026
- Published
- Sep 2025
Topics: Agent training and self-evolution , Search and deep research , Data and synthetic generation
Selection: 1kpapers.com by Together AI, most-cited as of Aug 9, 2026