Code fix · 4 checks · max 600 tokens · benched 2026-09-16
xAI models side by side on "Fix an off-by-one in Python": Grok 4.3 scores 10/10; Grok 4.3 is the cheapest answer scoring 8+ at $0.67 per 1,000 runs. Outputs, checks, judge reasons, latency and cost.
System
You are a senior engineer. Reply with code only unless asked otherwise.
User
This function should return the arithmetic mean of a non-empty list of numbers, but its result is wrong. Fix the bug with the smallest possible change and return the complete corrected function only, in a Python code block.
def average(nums):
total = 0
for n in nums:
total += n
return total / (len(nums) - 1)Rubric for the judge: Returns the full function with the divisor corrected to len(nums) and no other behavioural changes.
Every cell is one OpenRouter call at temperature 0 with the prompt's token cap and reasoning effort "low" where the model supports it. Cost is usage × the catalogue rate in models.json. Quality is one judge call to anthropic/claude-haiku-4.5 against the prompt's rubric, cached per prompt version.
x-ai/grok-4.6
303 in · 185 out (150 reasoning) · 18 words · checks 4/4
```python
def average(nums):
total = 0
for n in nums:
total += n
return total / len(nums)
```Judge: The output correctly fixes the bug by changing the divisor from len(nums) - 1 to len(nums), returns the complete function in a Python code block, and makes no other changes.
x-ai/grok-4.5
303 in · 100 out (65 reasoning) · 18 words · checks 4/4
```python
def average(nums):
total = 0
for n in nums:
total += n
return total / len(nums)
```Judge: The output correctly fixes the bug by changing the divisor from len(nums) - 1 to len(nums), returns the complete function in a Python code block, and makes no other changes.
x-ai/grok-4.20
279 in · 734 out (702 reasoning) · 18 words · checks 4/4
```python
def average(nums):
total = 0
for n in nums:
total += n
return total / len(nums)
```Judge: The output correctly fixes the bug by changing the divisor from len(nums) - 1 to len(nums), returns the complete function in a Python code block, and makes no other changes.
x-ai/grok-4.3
285 in · 206 out (174 reasoning) · 18 words · checks 4/4
```python
def average(nums):
total = 0
for n in nums:
total += n
return total / len(nums)
```Judge: The output correctly fixes the bug by changing the divisor from len(nums) - 1 to len(nums), returns the complete function in a Python code block, and makes no other changes.
Code fix: Returns the full function with the divisor corrected to len(nums) and no other behavioural changes. The deterministic checks are contains, regex, not_contains, not_contains.
If the judge's bar of 8/10 is good enough for you, Grok 4.3 at $0.67 per 1,000 runs. If you need the top score, Grok 4.3 at $0.67 per 1,000 runs.
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Re-run this prompt on xAI with your own OpenRouter key, or tweak the wording and see what changes.
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