OpenAI API (ChatGPT) → vLLM
What it saves, what actually moves, what you rebuild — and the thing that catches people.
What it costs, and what it saves
At scale the comparison flips: an H100 at roughly $2/hr serving continuously costs about $1,400/month and handles throughput that would cost far more per token via API. Below heavy sustained use, the API is cheaper.
Moves cleanly
Application code, via vLLM's OpenAI-compatible server. Same base-URL change as Ollama.
You rebuild
Prompts, plus the serving infrastructure Ollama would have hidden from you.
What OpenAI API (ChatGPT) costs you today
Usage-based per-token billing; ChatGPT Plus/Team/Enterprise seats on top
What actually holds you in
Proprietary models and API surface; your data and cost structure sit entirely on OpenAI's terms.
What you are moving to
vLLM is a fast inference and serving engine built for throughput, using paged attention to serve many concurrent requests efficiently. It is the choice when a team needs to self-host models at real scale.
Free / self-host
vLLM strengths
- Excellent throughput under concurrency
- OpenAI-compatible server mode
- Backed by a large community
What you give up
- Aimed at capable GPUs, not laptops
- Steeper operational learning curve
The migration, step by step
- 1Benchmark honestly: measure your actual tokens per day before assuming self-hosting is cheaper
- 2Rent a GPU and serve with vllm serve <model> --api-key <key>
- 3Point your OpenAI client at it
- 4Tune tensor parallelism and max_model_len for your GPU; defaults leave throughput on the table
- 5Add health checks and a supervisor, because nothing restarts it for you
The gotcha
vLLM is a throughput engine, not a convenience layer. It rewards understanding PagedAttention and batching and punishes treating it as a black box — the same GPU can differ severalfold in throughput on configuration alone.
When to stay on OpenAI API (ChatGPT)
Your volume is bursty or modest — a GPU idles at full price while an API bills zero.
Other ways off OpenAI API (ChatGPT)
More Layer 4 migrations
Figures verified 2026-07-04 against vendor pricing pages. Prices change and migrations differ by estate — treat the cost delta as a starting model, not a quote. Rankings and recommendations here are merit-only; affiliate income never changes a verdict. See our methodology.