What GPT-6 Luna means for AI agency chatbot costs
GPT-6 Luna runs a client chat conversation for about half a cent. Here is the math, what the model can't do (audio, for one), and why you shouldn't cut your monthly because of it.
A text chatbot for a local service business now costs a fraction of a cent per conversation to run on GPT-6 Luna, OpenAI's cheapest current model. OpenAI's model page lists it at $0.10 per million input tokens and $0.50 per million output tokens. For an agency, that means the model bill on a chat or SMS line is close to noise, and the number you should be pricing around is your own time. Voice is a different story, and I'll get to that.
Owners keep asking me whether a model that cheap is any good, so we read the model page and the Vapi changelog this week. The short answer is yes for scripted front-desk work, and no for anything that needs audio or a long chain of tool calls without care.
What did OpenAI actually release?
GPT-6 Luna is the small end of the GPT-6 family. OpenAI describes it as "our most efficient model for focused, high-volume tasks." Eesel's pricing write-up puts the launch on September 23, 2026, and I could not confirm that date on an OpenAI page, so treat it as secondhand.
I could confirm the rest on OpenAI's own page. Input is $0.10, cached input $0.01 and output $0.50, all per million tokens. The context window is 1,050,000 tokens, with 128,000 tokens of output. Text and images go in, text comes out, and audio is not supported. Batch and Flex tiers run at half the standard rate and fast mode at double. Function calling, structured outputs and streaming all work.
Vapi added it the week of October 5. Its changelog says gpt-6-luna is available for assistants in the API and dashboard, with reasoning support and a fast service tier. So if you build on Vapi, you can point an existing assistant at it today.
What does a chat conversation cost on it?
Vendor pages won't do this arithmetic for you.
Say a website chat runs ten customer messages. Your system prompt plus the business's services, hours and price bands is 3,000 tokens, and it gets sent on every turn along with the growing history. Each customer message is about 60 tokens and each reply about 120. Add it up across ten turns and you send roughly 38,100 input tokens and get back 1,200 output tokens.
At Luna's standard rates that is about $0.0038 for input and $0.0006 for output. Call it 0.44 cents. A thousand conversations come to about $4.41.
Those are my assumptions, not numbers from a client account. Swap in your own prompt length. Prompt caching would push the bill lower still. But even if I'm off by a factor of five, a client doing 300 chats a month is paying you for a model that costs them roughly a dollar.
Compare that to the platform you sell it on. Lumina's plan includes , and our wholesale tier for a website plus AI chatbot is $550 setup and $125 a month. The model is not where that money goes.