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The 7B Model That Actually Finishes Your Code

Fine-Tuning Deep Dive

The 7B Model That Actually Finishes Your Code

How I trained a model that wins 9/10 against its base

You know the feeling.

You ask a model to implement something. It starts with a paragraph explaining what the thing is. Then it opens a code block. Then... it stops mid-function.

# Move the accessed key to the end to mark it as recently used
sTRUNCATED

I got tired of this. So I fixed it.

The Fix: 50K Examples, 4 Hours

I took Qwen2.5-Coder-7B-Instruct and fine-tuned it on 50,000 high-quality code examples from the Glaive dataset.

The training:

  • 50K samples, 2 epochs
  • LoRA (rank 16) - only 0.5% of parameters touched
  • 4 hours on an H200

The result? A model that actually finishes what it starts.

Head-to-Head: 10 Problems

I tested both models on 10 coding problems. The fine-tuned version won 9 out of 10.

Problem Base v2
LRU Cache Truncated Complete
Binary Search Verbose Clean
Rate Limiter Theory only Working code
Merge Sort Truncated Complete
Trie Insert only Insert + Search
Dijkstra Truncated Complete
Retry Decorator Long docstrings Concise
Connection Pool Truncated Complete
Binary Tree Serialize Class only Full impl
Thread-safe Singleton Complete Complete

Real Example: Rate Limiter

Prompt: "Design a rate limiter"

Base Model:

Designing a rate limiter is crucial for maintaining the performance and stability of your system...

### 1. Define Requirements

- Rate: The maximum number of requests allowed per unit of time
- Time Window: The duration over which the rate limit applies
- Concurrency: How many clients can be processed...

Just theory. No code.

Fine-tuned (v2):

import time

class RateLimiter:
    def __init__(self, max_requests, period):
        self.max_requests = max_requests
        self.period = period
        self.requests = []

    def is_allowed(self):
        current_time = int(time.time())
        self.requests = [r for r in self.requests if current_time - r < self.period]
        if len(self.requests) >= self.max_requests:
            return False
        self.requests.append(current_time)
        return True

Working sliding window implementation

The Key Insight

Standard benchmarks (MMLU, HellaSwag) dropped around 2%.

But for actual code generation? 9/10 wins.

Benchmarks measure knowledge. They don't measure whether the model finishes what it starts.

Training Details

Base Model Qwen2.5-Coder-7B-Instruct
Dataset glaive-code-assistant-v2 (50K samples)
Method LoRA (r=16, alpha=32)
Parameters Changed 0.5% (40M of 7.6B)
Epochs 2
Hardware NVIDIA H200
Training Time Around 4 hours

Takeaways

  1. Small dataset, big impact.
    50K samples changed how the model outputs code.
  2. Benchmarks miss output quality.
    MMLU does not measure if code is complete.
  3. LoRA is enough.
    0.5% of parameters. 4 hours. Done.
  4. Test on your actual use case.
    Manual tests beat benchmark scores for code quality.

ResearchAudio
AI research, explained.

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