🚀 Zase o desetinku víc:
Proč jsou LLM benchmarky (často) mimo realitu?

AI Bootcamp 2026

Zdeněk Kasner | MFF UK

13 bře 2026

1

Výsledek záleží na tom, jak parsujeme odpovědi

Možnost č. 1: přímé generování písmena

prompt = f"""{question}
A) {a} B) {b} C) {c} D) {d}
Answer:"""

response = llm.generate(prompt)
# response = "The answer is C"
answer = parse_letter(response)

Možnost č. 2: písmeno s nejvyšší
pravděpodobností

prompt = f"""{question}
A) {a} B) {b} C) {c} D) {d}
Answer:"""

logprobs = llm.logprobs(
  prompt, tokens=["A","B","C","D"]
)
answer = argmax(logprobs)

Možnost č. 3: odpověď s nejvyšší
pravděpodobností

answers = [
f"{question}\nAnswer: {a}",
f"{question}\nAnswer: {b}",
f"{question}\nAnswer: {c}",
f"{question}\nAnswer: {d}",
]
cumulative_logprobs = [llm.cumulative_logprob(p) for p in prompts]
answer = argmax(cumulative_logprobs)

1) Přímé generování písmena

prompt = f"""{question}
A) {a} B) {b} C) {c} D) {d}
Answer:"""

response = llm.generate(prompt)
# response = "The answer is C"
answer = parse_letter(response)

2) Písmeno s nejvyšší pravděpodobností

prompt = f"""{question}
A) {a} B) {b} C) {c} D) {d}
Answer:"""

logprobs = llm.logprobs(
  prompt, tokens=["A","B","C","D"]
)
answer = argmax(logprobs)

3) Odpověď s nejvyšší pravděpodobností

answers = [
f"{question}\nAnswer: {a}",
f"{question}\nAnswer: {b}",
f"{question}\nAnswer: {c}",
f"{question}\nAnswer: {d}",
]
probs = [llm.score(p) for p in prompts]
answer = argmax(probs)

MMLU accuracy: 21.48%

MMLU accuracy: 34.44%

MMLU accuracy: 31.85%

skóre z blogu Sebastiana Raschky


Změna písmen mění i ranking modelů

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zdroj: Alzahrani et al. (2024)

Jak na free-form odpovědi?

  • Promptovat opravdu důrazně?
You answer HAS to be contained in the `\boxed{}` container.
  • Využít strukturovaný výstup?
{ ... answer: str ...} → { ... answer: "Alan Turing" ... }
  • Využít LLM-as-a-judge?
2

Modely lépe hodnotí samy sebe

LLM-as-a-judge

You are an a fair and impartial evaluator. Rate the following answer on a scale 1–5:

Question: {question}
Reference answer: {reference}
Model answer: {answer}

Respond with JSON:
{ "accuracy": <1-5>, "style": <1-5>, "completeness": <1-5> }

Self-recognition koreluje s self-preferencí

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zdroj: Panickssery et al. (2024)

Bias se liší podle modelů a jejich rodin

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zdroj: Spiliopoulou et al. (2025)

3

Číselná hodnocení z LLM-as-a-judge nejsou zkalibrovaná

Frequencies of some scores, such as 90 and 95, are far higher than 'odd' scores such as 92 or 19, and much of the range is almost entirely ignored (1-60).

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zdroj: Stureborg et al. (2024)

We asked an LLM to generate a score based on the % of words that had spelling errors. The results are not great, almost 80% of the quantitative range is scored as the same number.

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zdroj: @aparnadhinak

Jak to dopadne, když skóre přeformulujeme?

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zdroj: Li et al. (2025)


Další typy biasů

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zdroj: Ye et al. (2024)


A další...

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zdroj: Ye et al. (2024)

zdroj: Ye et al. (2024)

Biasy jsou v různé míře napříč modely

Náš výzkum: LLM-as-a-judge co má smysl

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články: Semin et al. (2026), Kasner et al. (2026), Kartáč et al. (2025), Kasner et al. (2024)

4

Modely mají testy namemorované

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https://github.com/lyy1994/awesome-data-contamination

  • Don’t Make Your LLM an Evaluation Benchmark Cheater
  • NLP Evaluation in trouble: On the Need to Measure LLM Data Contamination for each Benchmark
  • A Taxonomy for Data Contamination in Large Language Models
  • ...

alt text
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https://builtin.com/data-science/train-test-split

Našich 5 centů

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zdroj: Balloccu et al. (2024)

GSM1k

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zdroj: Scale AI (2024)

5

Benchmarky podléhají Goodhartovu zákonu

"When a measure becomes a target, it ceases to be a good measure."
— Charles Goodhart (1975)

  • Každý výzkumník a firma chtějí mít "state-of-the-art" skóre na benchmarku.
  • Všichni proto trénují modely především na příkladech, které se v nich objevují.
  • I trénování na podobných příkladech jako v test setu konkrétního benchmarku umožní modelu se v benchmarku zlepšit.

zdroj: Fodor (2025)

Na řadě benchmarků už není co zlepšovat

Benchmark Top skóre Saturovaný?
GSM8K 99 % ✅ Ano
MMLU 93 % ✅ Ano
HellaSwag 95 %+ ✅ Ano
GPQA Diamond 94.3 % ⚠️ Blízko
SWE-bench 80.8 % ❌ Zatím ne
Humanity's last exam 53.1 % ❌ Zatím ne

https://www.lxt.ai/blog/llm-benchmarks/

zdroj: Chollet (2019)

Zákon nešetří ani ty nejlepší...

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zdroj: Reddit

6

I LM arény se dají gejmovat

https://arena.ai

The leaderboard illusion (Singh et al., 2025)

Singh et al. (2025): The Leaderboard Illusion

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7

Agenti cheatují

Obejdou agenti i nesplnitelné unit testy?

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alt text

zdroj: Miller & Tang (2025)

agents often explicitly acknowledge discovering question-answer pairs
from HuggingFace within their reasoning chains

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zdroj: Scale AI (2025)

https://www.nist.gov/blogs/caisi-research-blog/cheating-ai-agent-evaluations

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  • Finding walkthroughs and answers for cyber CTF challenges online.
  • Using DDOS attacks to crash servers instead of exploiting vulnerabilities.
  • Cheating on coding benchmarks by looking up more recent code versions, disabling assertions, and adding test-specific logic.
8

Při evaluaci často neřešíme to, co je zásadní pro uživatele

https://informationisbeautiful.net/visualizations/the-rise-of-generative-ai-large-language-models-llms-like-chatgpt/

https://www.anthropic.com/research/labor-market-impacts

https://www.anthropic.com/research/labor-market-impacts

zdroj: Miller & Tang (2025)

As generative AI becomes increasingly embedded in everyday workflows,
it is important to evaluate its performance in ways that reflect real-world usage rather than abstract notions of intelligence

Among the six real-world capabilities we evaluate, Reviewing Work and Data Structuring are not captured at all by the metrics used in current AI benchmarking. Meanwhile, Summarization and Generation, capabilities widely used by non-technical professionals are only weakly supported.

zdroj: Miller & Tang (2025)


Metric Capability Accuracy Clarity Relevance
GSM8K Information Retrieval ~50% of questions were incorrect in early versions; improved later Focus is on producing the correct final answer, not explanation quality Covers elementary and middle school mathematics
MMLU-Pro Information Retrieval Reviewed for robustness with revised questions Same rigid answer format as MMLU Broader focus beyond US education
Math-500 Information Retrieval No known major errors in question set Explanation quality is not rated Focused entirely on mathematics
GPQA Information Retrieval 36% of questions have disagreement over the correct answer Exact formatting of answers is required Covers only biology, chemistry, and physics
Humanity's Last Exam Information Retrieval Written by experts, including PhDs Short answers must match exactly to count as correct Wide coverage, including niche historical and technical content

zdroj: Miller & Tang (2025)

Metric Capability Accuracy Clarity Relevance
SWE-bench Technical Assistance 32% of solutions used information from public comments; 31% had questionable test cases Requires the model to suggest a working patch that passes automated tests Focuses entirely on Python software development
WebDev Arena Technical Assistance No gold standard; judged by human preferences Clarity depends on how useful output is to humans Tasks involve real-world web development problems
Chatbot Arena Generation Responses compared by direct human voting Writing quality judged indirectly via preference Focused on imaginative, creative writing
Bird-SQL Technical Assistance Some inconsistencies in dataset, but no published error rate No penalties for unclear output Covers a wide range of database queries

Shrnutí

🚀 Zase o desetinku víc: Proč jsou LLM benchmarky (často) mimo realitu?



Zdeněk Kasner

ÚFAL MFF UK

zdenekkasner.cz

slidy zde:


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