Evidence from Youdao Translate suggests it deploys a machine-learning or NLP-based classifier alongside keyword rules: measured rules included repeated components (e.g., 螺+螺+螺+螺+螺+螺+蟢+D+哒+大) and nonsensical multi-token sequences that no human rule author would write, yet which consistently triggered censorship. Youdao returned 9,414 unique rules from the general test set — the most of any service — while also producing the most structurally anomalous rule patterns.

Across five popular translation services available in China (Alibaba, Baidu, Tencent, Youdao, and Microsoft Bing), researchers discovered 11,634 unique censorship rules in total. Every service — including the American-operated Bing Translate — implemented automatic censorship that silently omits content, with only Alibaba displaying any notification ('Query csi check not pass') to the user.

§6 Results / Table 2 evaluation

Alibaba and Bing Translate scan only the user's input text for censorship triggers, not the translation output, while Baidu and Tencent apply the same censorship rules to both input and output. Youdao censors input and output using different rule sets. Because Chinese-language censorship rules dominate all services' blocklists, users translating from a non-Chinese language into Chinese using Alibaba or Bing experience materially less censorship than users of the other services.

§7 Effect of Translator Output / Table 6 evaluation

Among 286 randomly sampled censorship rules across all five services, only one rule targeted erotic content, while the vast majority targeted political dissidents, CCP leaders, Tiananmen Square, Falun Gong, and government criticism. The paper interprets this near-total absence of pornography censorship as evidence that the censors did not anticipate their rules being audited, or are no longer interested in concealing the overtly political agenda of Chinese information control.

§6.2 Content Analysis / §6.2.6 Eroticism detection

On Tencent Translate, 15 distinct representations of Xi Jinping's name — including romanizations (xijinping, XiJinping, XIJINPING, xIDaDa, xidada), character variants (习近平, 习大大, 习主席, 习书记, 习总书记, 近平习, 反习大大), and a romanized reversed form (JinpingXi, jinpingxi) — each triggered censorship of the translator's entire output rather than just the offending sentence. Between 4–5% of Tencent's discovered rules were inconsistently enforced, which the paper attributes to load-balanced servers implementing different rule sets or rapid rule churn.

§6.3 Censorship Behavior / Table 5 detection

When the researchers attempted to use Gemini 2.5 Flash as a third independent LLM judge via its API for evaluating moderation decisions, Gemini automatically blocked all judging attempts citing safety reasons. This occurred even though the research task (judging whether a response is more or less moderated) does not itself produce harmful content. The incident illustrates that LLM safety systems can over-block legitimate research use cases, and that different LLM providers have different thresholds— Claude Haiku 4.5 and GPT-4o completed all judging tasks without safety refusals.

2026-lipphardt-dual §3.3.3 ml-classifierkeyword-filtering

Category-level analysis of 100 statements across 5 sensitive content categories found that interface-based moderation gaps vary significantly by topic. Sexuality showed the strongest WebUI/API gap (WebUI 7.0× more likely to be moderated than API per GPT-4o judge for Gemini). Political ideology followed at 2.0×, then hate speech at 1.0×. Miscellaneous offensive topics showed the inverse pattern (API more moderated at 0.3×). Religious content showed WebUI moderation with no API moderation. The pattern suggests public-facing WebUI interfaces prioritize reputational risk management for high-scrutiny categories.

2026-lipphardt-dual §4.5, Figure 8 ml-classifierkeyword-filtering

An empirical study of 100 sensitive statements tested on Gemini (2.5 Flash) and ChatGPT (GPT-5) found that WebUI interfaces are systematically more restrictive than their API counterparts. According to GPT-4o judge: WebUI was moderated 18% of the time vs. 9% (Gemini API) and 13% (ChatGPT API). DeBERTa classifier found 82% of WebUI responses moderated vs. 58% of API responses. The Gemini WebUI:API ratio ranged from 2.0:1 (GPT-4o) to 7.0:1 (Claude), and ChatGPT from 1.4:1 (GPT-4o) to 15.6:1 (Claude). Neither Google nor OpenAI discloses these interface-specific policies.

2026-lipphardt-dual §4.3, Table 2 ml-classifierkeyword-filtering

The paper proposes a black-box methodology for detecting censorship bias in LLMs by comparing responses to identical prompts in Simplified vs. Traditional Chinese — scripts for the same spoken language — controlling for translation quality while exploiting that Simplified Chinese training data is disproportionately sourced from mainland China's censored internet. Each prompt is repeated ten times and scored for similarity to censored text using an XLM-RoBERTa classifier fine-tuned on Baidu Baike (censored) vs. Chinese Wikipedia (uncensored) with scores from 0 to 1.

2024-ahmed-extended §2 / §2.4 keyword-filteringml-classifiermeasurement-platform

China's local censorship operates through 'extra-institutional governance' (EIG) — practices that transgress the official identity and authorized means of the CAO system, including outsourced private surveillance, unpaid personnel secondment, and mass reporting via personal accounts — which upper-level offices tolerate but do not formally authorize, preserving plausible deniability when practices are ethically or legally questionable. The paper documents these as widespread implicit norms across China, not isolated to District T.

2024-zhang-toothless §Discussion and Conclusion keyword-filteringml-classifier

A county-level CAO in east China (District T, ~500,000 residents) operated with only 7 formal employees yet was tasked with monitoring more than 60 social media platforms, detecting unwanted voices in text, image, video, and audio formats, and submitting hourly reports to upper-level offices — a workload the authors characterize as a 'mission impossible' for a county-level office.

2024-zhang-toothless §The case: the CAO in District T keyword-filteringml-classifier