GPT-5.4 mini (March 2026) is OpenAI's fast, low-cost model with a 400K-token context window, optimized for coding, tool calling, and image reasoning. It runs 2×+ faster than GPT-5 mini while approaching the larger GPT-5.4 on several benchmarks.
Available free to start via Vercel AI Gateway ($5/month in credits, no credit card) — a great pick for strong capability at high speed and low cost.