Cheapest LLM API for a chatbot.

What a customer-support or chat assistant costs on each model.

A typical chatbot turn is about 1,000 input tokens (system prompt plus history) and 500 output tokens. At 100,000 chat turns a month:

GPT-OSS 20B on Groq: $22.50
GPT-5 nano: $25.00
Gemini 2.5 Flash-Lite: $30.00
GPT-6 Luna: $35.00
Claude Haiku 5.5: $35.00

Your system prompt repeats on every turn, so prompt caching matters. Cached input on Claude Sonnet 5.5 is $0.10 per 1M versus $2 uncached, per Anthropic. Set the "Cached input %" field in the calculator to see the effect.

All prices from official provider pages, checked Oct 20, 2026. See sources.