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ARC (AI2 Reasoning Challenge)

Overview

Property Value
Benchmark ID arc
Dataset allenai/ai2_arc
Tasks 7,787 questions (Challenge + Easy)
Evaluation Letter match against answer key
Output Type Single letter (A-E)
Timeout 60-180 seconds

Quick Start

mcpbr run -c config.yaml --benchmark arc -n 20

Overview

The AI2 Reasoning Challenge (ARC) is a benchmark consisting of 7,787 genuine grade-school level science questions assembled from standardized tests. The dataset is partitioned into two subsets:

  • ARC-Challenge (default): 2,590 questions that require multi-step reasoning, scientific knowledge, and cannot be answered through simple statistical co-occurrence or retrieval methods. These questions were specifically filtered to be difficult for both retrieval-based and word co-occurrence algorithms.

  • ARC-Easy: 5,197 questions that are answerable with simpler approaches. While still grade-school science questions, they tend to require less complex reasoning.

Each question is multiple-choice with 3 to 5 answer options labeled with letters (A through E) or occasionally numbers (1 through 5). The questions cover topics such as:

  • Physical science (forces, energy, matter)
  • Life science (biology, ecosystems, human body)
  • Earth and space science (weather, geology, astronomy)
  • Scientific reasoning and experimental design

ARC is useful for evaluating:

  • Scientific knowledge at a foundational level
  • Multi-step reasoning ability
  • Question comprehension and inference
  • Answer selection from plausible distractors

Task Structure

Each ARC task contains the following fields:

  • id: Unique question identifier
  • question: The science question text
  • choices: An object with label (list of letters) and text (list of answer texts)
  • answerKey: The correct answer letter (e.g., "A", "B", "C", "D", or "E")

The agent receives the question with all labeled answer options and must respond with the letter of the correct answer.

Example Task

Answer the following science question:

A student is studying the properties of different materials. Which of the
following is the best conductor of electricity?

Options:
  (A) Glass rod
  (B) Copper wire
  (C) Rubber band
  (D) Wooden stick

Correct Answer: B

Running the Benchmark

# Run ARC-Challenge (default)
mcpbr run -c config.yaml --benchmark arc

# Run a small sample
mcpbr run -c config.yaml --benchmark arc -n 20

# Run ARC-Easy subset
mcpbr run -c config.yaml --benchmark arc --filter-difficulty easy

# Explicitly run ARC-Challenge
mcpbr run -c config.yaml --benchmark arc --filter-difficulty challenge

# Run with verbose output and save results
mcpbr run -c config.yaml --benchmark arc -n 50 -v -o results.json

benchmark: "arc"
sample_size: 10
timeout_seconds: 120

# Optional: select the Easy subset instead of Challenge
filter_difficulty:
  - "easy"

Difficulty Filtering

ARC uses filter_difficulty to select between the two subsets:

Filter Value Subset Questions Description
challenge ARC-Challenge 2,590 Hard questions requiring reasoning (default)
easy ARC-Easy 5,197 Simpler questions answerable with retrieval

When no filter_difficulty is specified, ARC-Challenge is used by default. If multiple values are provided, the last recognized value takes precedence.

Evaluation Methodology

ARC evaluation uses letter-matching:

  1. Answer extraction: The evaluation uses a regex pattern \b([A-E1-5])\b to find all standalone letters (A-E) or digits (1-5) in the model's uppercase response.

  2. Last-match selection: The last matching letter or digit is used as the model's answer. This accommodates reasoning where the model discusses multiple options before settling on a final answer.

  3. Case-insensitive comparison: The extracted answer is compared to the answerKey field. Both are uppercased before comparison.

Scoring

resolved = (extracted_answer.upper() == answer_key.upper())

Where: - extracted_answer: Last letter in [A-E] or digit in [1-5] found via regex - answer_key: The correct answer from the dataset

Answer Format

The model should respond with a single letter. The evaluation handles various response formats:

  • "B" (direct answer)
  • "The answer is B." (sentence format)
  • "B) Copper wire" (letter with option text)
  • "After analyzing the options, I believe the answer is B because copper is a metal and metals conduct electricity." (reasoned answer)

Example Output

Successful Evaluation

{
  "resolved": true,
  "agent_answer": "B",
  "correct_answer": "B"
}

Failed Evaluation (Wrong Answer)

{
  "resolved": false,
  "agent_answer": "A",
  "correct_answer": "B"
}

Failed Evaluation (No Answer Extracted)

{
  "resolved": false,
  "error": "Could not extract answer from solution"
}

This occurs when the model's response does not contain any standalone letter in A-E or digit in 1-5.

Troubleshooting

Model discusses all options without clear final answer

If the model provides analysis of each option without stating a final letter, the regex extraction uses the last letter mentioned, which may be incorrect. Configure your prompt to enforce a clear final answer:

agent_prompt: |
  {problem_statement}

  Think through the science carefully, then respond with ONLY the letter of the correct answer (A, B, C, D, or E).

Evaluation extracts wrong letter from verbose response

Since the evaluation takes the last letter match, a response like "The answer is B. Options A and D are clearly wrong." would extract D instead of B. Instruct the model to place its final answer at the end of the response, or to respond with only the letter.

Switching between Challenge and Easy returns unexpected counts

When using filter_difficulty, ensure you pass exactly one value. If both "easy" and "challenge" are specified, the implementation checks for "easy" first, then "challenge". The last matching condition sets the subset.

Questions with numeric answer labels (1-5)

Some ARC questions use numeric labels (1, 2, 3, 4, 5) instead of letters (A, B, C, D, E). The evaluation handles both formats automatically through the regex pattern.

Best Practices

  • Use ARC-Challenge for meaningful evaluation: ARC-Easy questions can often be answered through pattern matching. ARC-Challenge provides a more discriminating measure of scientific reasoning.
  • Keep answers concise: Single-letter responses eliminate extraction errors. If you need reasoning, instruct the model to state the letter first, then explain.
  • Start small: Run 10-20 questions from each subset to establish a baseline before running larger evaluations.
  • Compare subsets: Running both ARC-Challenge and ARC-Easy provides a useful difficulty gradient. Large accuracy gaps between the two subsets indicate the model may be relying on shortcuts rather than genuine reasoning.
  • Short timeouts are sufficient: ARC questions are straightforward multiple-choice. A timeout of 60-120 seconds is typically more than enough.
  • Use for rapid model comparison: ARC's well-established baselines and simple evaluation make it excellent for quickly comparing model capabilities before investing in more expensive benchmarks.