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GPT-6 Luna vs Gemini 3.5 Flash-Lite API Cost

The two cheapest small models head to head: GPT-6 Luna at $0.10/$0.50 and Gemini 3.5 Flash-Lite at $0.30/$2.50 per million tokens.

Updated · By Niraj Kumar · 6 sources

Models

Each request

Count text inCount text in
tokens

System prompt, conversation history, documents and tool definitions are all resent on every call.

tokens

The visible answer.

Count tokens from a prompt or JSON payloadShow

Plain text, OpenAI Chat or Responses JSON, or Anthropic Messages JSON. A final assistant message or a response body counts as output. Counted in your browser; nothing is uploaded.

Loading the tokenizer…

Counts use OpenAI's o200k tokenizer, so they are exact for GPT-6 and GPT-5 models, plus a few tokens of message framing. Other providers' tokenizers count the same text differently and do not publish a conversion factor; Anthropic says Claude models from 4.7 on produce about 30% more tokens than earlier Claude models. For an exact count on another model, paste one of its API responses: the usage it reports is shown above.

tokens

Thinking tokens are billed as output. Leave at 0 for models or settings that do not reason.

Volume

PricePrice

30,000 requests over 30 days.

Discounts

%
0%100%

The share of input that repeats exactly at the start of every request, such as a fixed system prompt. The prompt caching calculator prices cache writes and expiry in detail.

Batch APIBatch API
Cheaper for this workloadGPT-6 Luna74% less, saving $48.00 a month
GPT-6 Luna
$16.50 a month
$0.00055 a request · 2nd cheapest of 24
Gemini 3.5 Flash-Lite
$64.50 a month
$0.00215 a request · 7th cheapest of 24
At 10× the volume
$480.00 a month apart
Cheapest listed model
Claude Haiku 5.5
$16.50 a month
Side by side
MeasureGPT-6 LunaGemini 3.5 Flash-Lite
Input, per 1M tokens$0.10$0.30
Cache hit, per 1M tokens$0.01$0.03
Output, per 1M tokens$0.50$2.50
Context window1.05M tokens1.05M tokens
Max output128K tokens65.5K tokens
Batch discount50%50%
Long-context surchargeAbove 272K inputNone
Input cost a month$9.00$27.00
Output cost a month$7.50$37.50
Every model on this workload, per month3,000 tokens in, 500 out, 1,000 a day. Hover or focus a row for rates.
  1. 1Claude Haiku 5.5Anthropic$16.50
  2. 2GPT-6 LunaOpenAI$16.50
  3. 3Qwen3.8 FlashAlibaba$20.55
  4. 4GPT-5.6 LunaOpenAI$36.00
  5. 5DeepSeek V4.1 FlashDeepSeek$45.00
  6. 6Qwen3.7 PlusAlibaba$60.00
  7. 7Gemini 3.5 Flash-LiteGoogle$64.50
  8. 8Gemini 3.8 FlashGoogle$123.75
  9. 9Grok 4.3xAI$150.00
  10. 10Claude Haiku 4.5Anthropic$165.00
  11. 11DeepSeek V4 ProDeepSeek$178.20
  12. 12Grok 4.7xAI$270.00
  13. 13Qwen3.8 MaxAlibaba$270.00
  14. 14Claude Sonnet 5.5Anthropic$330.00
  15. 15Claude Sonnet 5Anthropic$330.00
  16. 16GPT-6.1 SolOpenAI$330.00
  17. 17GPT-6 SolOpenAI$330.00
  18. 18GPT-5.6 TerraOpenAI$360.00
  19. 19Gemini 3.1 ProGoogle$360.00
  20. 20Claude Opus 5.5Anthropic$660.00
  21. 21GPT-5.6 SolOpenAI$660.00
  22. 22Claude Opus 5Anthropic$825.00
  23. 23Claude Fable 5.1Anthropic$1,650
  24. 24GPT-6 AstraOpenAI$1,650

How the GPT-6 Luna vs Gemini 3.5 Flash-Lite API Cost works

cost = (fresh input × input rate + cached input × cache rate + (output + reasoning) × output rate) ÷ 1,000,000

This page uses the same method as the LLM API Cost Calculator, which explains each term and assumption in full.

Worked example

A chat feature sending 3,000 input tokens and getting 500 back, 1,000 times a day, priced on both models with no caching.

  1. 1GPT-6 Luna: 3,000 × $0.10 + 500 × $0.50, ÷ 1,000,000 = $0.00055 a request, $16.50 a month
  2. 2Gemini 3.5 Flash-Lite: 3,000 × $0.30 + 500 × $2.50, ÷ 1,000,000 = $0.00215 a request, $64.50 a month
  3. 3Difference: $48.00 a month

GPT-6 Luna is $48.00 a month cheaper for this workload, 74% less.

Frequently asked questions

Which is cheaper, GPT-6 Luna or Gemini 3.5 Flash-Lite?

At standard list rates, GPT-6 Luna is 74% cheaper than Gemini 3.5 Flash-Lite on a typical chat request (3,000 tokens in, 500 out); GPT-6 Luna is 80% cheaper than Gemini 3.5 Flash-Lite on output-heavy generation (500 in, 2,000 out); and GPT-6 Luna is 74% cheaper than Gemini 3.5 Flash-Lite on a large cached prompt (20,000 in, 90% cached, 500 out). GPT-6 Luna charges $0.10 input and $0.50 output per million tokens; Gemini 3.5 Flash-Lite charges $0.30 and $2.50.

Is GPT-6 Luna always cheaper than Gemini 3.5 Flash-Lite?

Below 272,000 tokens, yes: Luna's input is a third of Flash-Lite's price and its output a fifth. Above that, Luna bills the whole request at $0.20 input and $0.75 output, still below Flash-Lite's flat $0.30 and $2.50. Choose between them on quality, latency and where your data can be processed rather than on price.

Sources

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