Official UPSC position:

The Civil Services Examination Rules explicitly state that medium of answers shall not be used as a criterion for evaluation. UPSC appoints separate evaluators for each language medium, and the marking scheme is content-based.

Empirical observations:

While UPSC does not publish medium-wise average score data, several RTI responses and academic studies (including one published in Economic & Political Weekly, 2019) suggest:

• English-medium candidates have slightly higher average scores in GS papers
• The gap is attributed primarily to: (a) better availability of English-medium coaching and test series, (b) technical terminology ease, (c) more extensive reading material
• Hindi-medium toppers exist at all rank levels, including top 50

The real disadvantage of regional/Hindi medium:

• Test series in Hindi are fewer and often less rigorous
• Model answers and topper copies circulated online are overwhelmingly in English
• Essay paper: English essays get more reviewer attention in media, so benchmarking is harder for Hindi aspirants

What helps non-English medium candidates:

• Use parenthetical technique for technical terms: write the term in English in parentheses after the Hindi equivalent
• Study Drishti IAS and Drishti magazine for Hindi GS coverage
• Join a Hindi-medium test series (Vision IAS and ForumIAS offer Hindi variants)
• Read Hindi-medium topper copies (available on UPSC website post-result)