Backend Engineer Cuts LLM Costs 95% by Switching from GPT-4o to Cheaper Alternatives

A backend engineer running a hobby RAG pipeline on GPT-4o was spending roughly $750 per month on API costs, prompting him to evaluate cheaper model alternatives. After benchmarking 200 question-answer pairs, he found DeepSeek V4 Flash scored 0.89 accuracy compared to GPT-4o's 0.91, at a fraction of the cost — $0.25 per million output tokens versus $10.00. He migrated his stack in a single afternoon using Global API, an OpenAI-compatible gateway that routes requests to 184 models without requiring any SDK changes. The same monthly workload on DeepSeek V4 Flash would cost approximately $32.85, representing over 95% in savings. The engineer cautioned that accuracy trade-offs vary by use case and recommended others run their own evaluations before switching models.