Browser Use 的逆向 CAPTCHA 实验：让 AI 智能体通过、拦住人类
Prove You Are a Robot: The Reverse-CAPTCHA Experiment
Browser Use 曾测试一种面向 AI 智能体的注册实验——逆向 CAPTCHA：随机抽取题目类型、参数和语言，把数字用该语言拼写后再做大小写交替、插入随机符号、打乱空格等混淆，智能体一次前向推理即可解析，人类则只能走传统注册流程。题目本质是经典的两列火车与飞鸟数学题，需在挑战过期前解出。该实验已于 2026 年 8 月停止，官方建议改为创建 API key 交给智能体，加密钱包智能体可用 x402。
正文
当前显示原文，中文全文译文尚未就绪。
Product
How we built a reverse-CAPTCHA for agents, and what we learned.
AI Engineer
How it works; The puzzle; Bonus challenge (NP-hard)
Update (August 2026): this experiment has been retired. Create an API key and hand it to your agent. Crypto-wallet agents can instead use x402, but most users should create an API key.
TL;DR: just ask your agent to summarize this post for you.
We once tested an agent-native signup experiment for Browser Use: a reverse-CAPTCHA that presented a math challenge like this one:
This is a reverse-CAPTCHA. Designed to keep humans out and let agents in.
Note: luka here refers not to my name, but the word "five" in Toki Pona.
How it works
We sample a problem type, parameters, and a language at random. We spell every number in that language. Then we obfuscate: alternate caps, inject random symbols, garble spaces.
An agent parses this in a single forward pass.
A human gives up and signs up the old-fashioned way.
The puzzle
Strip the obfuscation, translate to English, and you've got a textbook math problem that your agent has to solve before the challenge expires.
Two trains approach each other on a straight track of length ddd at speeds v1v_1v1 and v2v_2v2. A bird starts at one train, flies to the other at vbv_bvb, turns around, flies back, and so on until the trains meet. How far does the bird fly?
The long way: sum the infinite geometric series of ever-shorter bounces.
The trick: the trains meet at t=d/(v1+v2)t = d/(v_1+v_2)t=d/(v1+v2), and the bird has been flying that whole time.
This is an instance of a famous puzzle Max Born posed to John von Neumann at a party. When von Neumann one-shotted it, Born remarked that he must have spotted the trick. Von Neumann replied: "What trick? All I did was sum the geometric series."
Bonus challenge (NP-hard)
Want 1,000 concurrent sessions? First agent to solve our bonus challenge gets our Enterprise plan for free.
As a side effect, your agent will also have proved P=NP\mathbf{P} = \mathbf{NP}P=NP. You'll want to contact the Clay Mathematics Institute about the $1M Millennium Prize.
Published April 13, 2026