Technical
2026-03-038 min read

RAG vs Fine-Tuning: When to Use Each

Build a chatbot that knows your data? That's RAG. Want AI that sounds like your brand? That's fine-tuning. Here's when to use which.

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The Two Paths to Custom AI

When you want AI that knows your stuff, you have two main options:

  • RAG (Retrieval-Augmented Generation) — Feed context at runtime
  • Fine-tuning — Train the model on your data
  • Let's break down each.

    RAG: The Quick-Start Approach

    How It Works

  • Split your documents into chunks
  • Embed them into vectors
  • At runtime, retrieve relevant chunks
  • Feed them to the LLM as context
  • Pros

  • Fast to implement (days, not weeks)
  • Can update knowledge instantly
  • No training costs
  • Works with any LLM
  • Cons

  • Context window limits apply
  • Retrieval quality = output quality
  • Can be slower (extra API call)
  • Best For

  • FAQ bots
  • Document Q&A
  • Knowledge base assistants
  • Anything needing current data
  • Fine-Tuning: The Deep Customization

    How It Works

  • Gather training data (prompts + responses)
  • Train a base model on your data
  • Deploy the fine-tuned model
  • Pros

  • Model "knows" your style natively
  • Faster inference (no retrieval)
  • Can learn complex patterns
  • Works without context
  • Cons

  • Expensive (training costs + hosting)
  • Slow to update (retrain required)
  • Needs lots of quality data
  • Overfitting risk
  • The Hybrid Approach (Our Recommendation)

  • Start with RAG — Get something working fast
  • Add fine-tuning later — Once you have data and know what matters
  • Use both — Fine-tuned model for core capability, RAG for up-to-date info
  • Our Take

    For 90% of SMEs: Start with RAG.

    It's faster, cheaper, and easier to maintain. Fine-tune only when you have:

  • Clear ROI from customization
  • Enough data (100s-1000s of examples)
  • Need for sub-second responses at scale
  • Ready to put this into practice?

    Start tracing your AI agents in 5 minutes with Trefur Observe.