For the past year, open-source web agents have looked like dinghies chasing aircraft carriers: even 70-billion-parameter models scraped single-digit accuracy on BrowseComp-en, the field’s toughest information-seeking benchmark, while closed systems such as DeepResearch and Grok-3 cruised far ahead. Tongyi Lab, Alibaba’s applied-AI skunkworks, says it has all but closed that gap with WebSailor, a post-training recipe that rewires large language models to “think like uncertainty-slayers.”
Turning the web into a maze on purpose
At the heart of WebSailor is SailorFog-QA, a synthetic dataset that bombards the model with “Level-3” problems—questions whose answers hide behind tangled entity graphs and deliberately obfuscated clues (“a musician later honored in the early 21st century,” “a chronology that ends the same year a late-antique poet died”). Random walks over real web pages build those graphs; masking, vagueness and partial names turn each query into a fog bank the agent must burn off through multi-step reasoning.
DUPO: reinforcement learning that isn’t painfully slow
Tool-using agents learn painfully slowly because every step calls a browser, but Tongyi Lab’s Duplicating Sampling Policy Optimization (DUPO) makes each RL batch pull double duty: one pass samples harder trajectories, the next re-samples mid-episode to squeeze more signal from sparse rewards. A small rejection-sampling fine-tuning (RFT) “cold start” of just 2 k expert traces primes the model so DUPO has something to optimize.
Four sizes, one giant leap
WebSailor comes in 3B, 7B, 32B and 72B flavors. Even the 7-billion-parameter version hits 6.7 % pass@1 on BrowseComp-en, trouncing agents built on 32 B backbones that manage barely 2 – 3 %. The 32 B and 72 B models push further, outscoring open-source peers on BrowseComp-en/zh, GAIA and XBench and edging past proprietary offerings like Grok-3 and Doubao-Search when those systems add browsing tools.
Why it matters
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Democratizing deep search. BrowseComp-level tasks—ask a question, navigate dozen-plus pages, synthesize an answer—are what corporate knowledge-bases and vertical search startups need. WebSailor shows you no longer need a closed-source giant to play.
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A recipe, not a model. The CPT + HCF routine, uncertainty-first data and DUPO optimizer are architecture-agnostic; any ReAct-style agent with tool APIs can adopt them.
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Downward compatibility. Despite training only on headache-grade puzzles, WebSailor’s 72 B model scores >90 % pass@1 on the single-hop SimpleQA benchmark, proving that hard-first curricula don’t break easy tasks.
Open weights, open benchmark
Code, data-generation scripts and checkpoints live in Tongyi Lab’s GitHub repo, alongside a dockerized evaluator so outside teams can reproduce—or dispute—the numbers.
With WebSailor, the open-source fleet finally has a flagship capable of keeping proprietary juggernauts in sight. The real question now: how long before someone splices SailorFog-style data and DUPO into a general-purpose agent that can shop, schedule and navigate enterprise wikis with the same super-human calm?
Paper link: arXiv 2507.02592 (PDF)
