Our Melbourne LLM fine-tuning methodology produces domain-specific models that are accurate, efficient, and governable. Data preparation is the foundation of successful fine-tuning. We follow a rigorous data pipeline: source identification (identifying the corpus that contains the domain knowledge the model needs — regulatory documents, policy wordings, claims decisions, clinical guidelines, legal opinions, customer correspondence, training materials — and assessing data quality, volume, and representativeness), de-identification (for corpora containing personal information: systematic removal of personal identifiers — names, addresses, dates of birth, account numbers, policy numbers, Medicare numbers, TFN — while preserving the linguistic patterns and domain terminology the model needs to learn; we use a combination of NER-based automated de-identification and rule-based pattern matching, with human review of a statistical sample to validate de-identification completeness), data formatting (converting source documents into the instruction-response format required for fine-tuning — each training example consists of an instruction (what the model should do), input (the context or data the model works with), and output (the correct response); for claims determination, this means: instruction "Determine whether this claim is covered under the policy," input (the claim description and relevant policy extract), output (the coverage determination with reasoning)), quality filtering (removing low-quality, contradictory, or outdated examples — a claims determination that was later overturned on review, a regulatory interpretation superseded by updated guidance, a template response that does not reflect current practice), and augmentation (generating additional training examples for underrepresented scenarios — rare claim types, edge-case regulatory interpretations, unusual document formats — using synthetic data generation guided by domain experts). Base model selection considers: capability (the base model must have sufficient reasoning capability for the target task — a 7B parameter model may suffice for classification tasks but complex reasoning tasks like claims determination may require 13B+ or 70B), licensing (open-source models like Llama, Mistral, and Qwen have different licensing terms for commercial use — we ensure the selected base model licence permits the intended deployment), language capability (base models vary in their English language quality and their ability to handle Australian English specifically — models with strong English training data perform better after fine-tuning on Australian content), and deployment constraints (on-premise deployment on available hardware — a 70B model requires significantly more GPU memory than a 7B model; the model must fit within the organisation's infrastructure constraints). Fine-tuning execution uses parameter-efficient methods. LoRA (Low-Rank Adaptation): rather than updating all model parameters (billions of weights), LoRA adds small trainable adapter layers — typically 0.1-1% of the total parameters. The base model weights remain frozen while the adapters learn the domain-specific knowledge. Benefits: dramatically reduced compute cost (hours rather than weeks), reduced storage (the adapter is typically 10-100MB rather than the full model size of 10-140GB), and the ability to swap adapters (the same base model can serve multiple domains by loading different adapters). QLoRA: combines LoRA with 4-bit quantisation of the base model — enabling fine-tuning of 70B parameter models on a single A100 GPU (which would otherwise require 4-8 GPUs). This makes large model fine-tuning accessible to Melbourne enterprises without massive GPU infrastructure. Training monitoring: we track training loss, validation loss, and domain-specific evaluation metrics throughout training — detecting overfitting (the model memorises training examples rather than learning generalisable patterns) and underfitting (insufficient training to capture the domain knowledge). Evaluation uses domain-specific benchmarks. We create evaluation datasets that test the fine-tuned model on realistic tasks: accuracy benchmarks (a held-out set of examples the model was not trained on — measuring how accurately the model performs the target task on unseen data), comparison benchmarks (the same evaluation set tested on both the fine-tuned model and the base model — quantifying the improvement from fine-tuning), adversarial benchmarks (deliberately challenging examples designed to test edge cases — ambiguous coverage scenarios, conflicting regulations, unusual document formats), and human evaluation (domain experts reviewing model outputs for accuracy, completeness, tone, and regulatory compliance — particularly important for models that will generate customer-facing content or regulatory submissions).