When to use a custom AI model vs the OpenAI API — a practical framework
When to use a custom AI model vs the OpenAI API — a practical framework
Web & App Development • technical guide
Table of Contents
What commercial APIs give you out of the box
Commercial LLM APIs (OpenAI GPT-4o, Anthropic Claude 3.5 Sonnet) provide state-of-the-art reasoning, multimodal capabilities, and zero infrastructure setup. For 90% of business applications, commercial APIs deliver the fastest time-to-market.Need a custom quantitative solution?
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- General business chat and lead intake. - Document processing and summary workflows. - Code generation and standard function calling pipelines.When you genuinely need a custom fine-tuned model
1. **Strict Data Privacy / On-Premise Requirements**: Healthcare, defense, or banking data that cannot cross third-party external networks under any circumstances. 2. **Extreme Token Volume at Scale**: Processing tens of millions of monthly requests where API token fees exceed server GPU hosting costs. 3. **Niche Domain Specialization**: Sub-specialized medical diagnostics, proprietary financial code, or unique structured formatting.Simple decision framework
1. Is data permitted to leave your cloud network via encrypted API? **Yes -> Use OpenAI / Claude**. 2. Is token volume under 5 million requests per month? **Yes -> Use OpenAI / Claude**. 3. Do you require sub-50ms specialized local inferencing or 100% offline deployment? **Yes -> Fine-Tune Custom Open-Source Model**.About the PSI Square Team
We are a team of quantitative developers, AI system architects, and full-stack software engineers specializing in execution latency optimization, autonomous systems orchestration, and custom broker integrations.
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