Our Melbourne GPT integration projects cover use case identification, model selection, implementation, guardrails, and optimization. Use case identification (week 1): determining where GPT provides real value. We evaluate potential use cases on: impact (how much time or cost does this save? How much quality improvement?), feasibility (can GPT actually do this well? We prototype quickly — testing the use case with real data to verify LLM capability before committing to full implementation), risk (what happens if GPT gets it wrong? Low-risk: marketing copy draft that a human reviews. High-risk: medical advice that a patient acts on. We prioritize low-risk, high-impact use cases first), and data requirements (does the use case require company-specific data? If yes: RAG or fine-tuning. If no: prompt engineering with the base model may suffice). Model selection (week 1): choosing the right LLM for each use case. GPT-4o (OpenAI): best general-purpose model — strong reasoning, good at following complex instructions, excellent code generation. Cost: USD 2.50/million input tokens. Best for: document processing, content generation, code assistance. Claude 3.5 Sonnet (Anthropic): strong at analysis and nuanced writing — often preferred for long document processing and situations requiring careful reasoning. Best for: contract review, research synthesis, compliance analysis. GPT-4o-mini (OpenAI): cost-effective for simpler tasks — 15x cheaper than GPT-4o. Best for: classification, simple extraction, customer service (where query complexity is low). Open-source (Llama 3, Mistral): for use cases requiring on-premises deployment (data that cannot leave the organization's infrastructure). Best for: healthcare (patient data), financial services (transaction data), government (classified data). Trade-off: lower performance than GPT-4o/Claude, but data never leaves your infrastructure. Implementation (weeks 2-5): building the GPT integration. API integration: connecting the LLM to the business application — OpenAI API, Anthropic API, or self-hosted open-source model. Architecture: application → API gateway (rate limiting, authentication, logging) → LLM provider. Response handling: structured output parsing (using JSON mode or function calling to get structured responses rather than free-text), error handling (API timeouts, rate limits, model errors — graceful degradation rather than application crashes), and cost tracking (monitoring token usage per user and use case — preventing unexpected API bills). RAG (Retrieval-Augmented Generation): for use cases requiring company-specific knowledge. Implementation: document ingestion (processing company documents — PDFs, Word docs, web pages, database records — into text chunks), embedding (converting text chunks into vector embeddings using OpenAI embeddings or open-source alternatives), vector storage (Pinecone, Weaviate, or pgvector — storing embeddings for efficient similarity search), and retrieval (when a user asks a question, finding the most relevant document chunks and providing them to the LLM as context for generating the answer). Prompt engineering: carefully crafted system prompts defining the LLM's behavior — persona (what role does the LLM play?), constraints (what should it NOT do? What topics are off-limits?), output format (structured responses, specific formats, length limits), and examples (few-shot examples demonstrating the expected input/output pattern). Guardrails (weeks 3-5): preventing GPT from causing harm. Content filtering: blocking inappropriate, harmful, or off-topic responses — using OpenAI's moderation API plus custom rules for business-specific restrictions. Hallucination mitigation: RAG (grounding responses in company data), confidence scoring (the LLM indicating when it's uncertain), source attribution (the LLM citing which documents support its answer), and human-in-the-loop (for high-risk use cases — LLM generates draft, human reviews and approves before it reaches the end user). Privacy controls: ensuring personal information is handled appropriately — PII detection and redaction before sending data to external LLM APIs (if using cloud-based models), data processing agreements with LLM providers (OpenAI and Anthropic both offer enterprise agreements with data processing commitments), and audit logging (recording what data was sent to the LLM, what response was received, and who accessed it). Australian-specific: Privacy Act compliance documentation, APRA notification for financial services use cases, and Australian English configuration (system prompts instructing the LLM to use Australian spelling, terminology, and cultural references). Optimization (ongoing): improving performance and reducing costs. Prompt optimization: iterating on prompts based on real-world performance data — improving answer quality, reducing hallucination rate, and adjusting tone. Model optimization: evaluating newer models as they're released (the LLM landscape evolves rapidly — a model released 6 months ago may be outperformed by a cheaper, faster alternative today), using smaller models for simple tasks (GPT-4o-mini instead of GPT-4o where quality is sufficient — 15x cost reduction). Caching: caching common responses (if many users ask similar questions, the cached response is served without an LLM API call — reducing cost and latency). Evaluation: systematic measurement of LLM output quality — human evaluation of response accuracy, user satisfaction tracking, and A/B testing of different prompts and models.