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GPT-6 Luna vs Gemini 3.1 Flash-Lite: API Cost Comparison

Budget tiers from OpenAI and Google for bulk classification and extraction.

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Updated 7 Nov 2026

GPT-6 Luna and Gemini 3.1 Flash-Lite pricing side by side
Side by side	GPT-6 Luna OpenAI	Gemini 3.1 Flash-Lite Google
Input / 1M	$0.10	$0.25
Output / 1M	$0.50	$1.50
Cached input / 1M	$0.01	Not modelled
Batch discount	50% off	50% off
Context window	1.05M tokens	1.05M tokens
Long-prompt surcharge	Above 272K input	None
Tier	Small / fast	Small / fast

Workload

Requests per day

Avg input tokens

tok

Avg output tokens

tok

Cached input

Repeated system prompt or docs

Batched requests

Jobs that can wait hours

Models

Anthropic

OpenAI

Google

Mistral

DeepSeek

$ per 1M tokens, input / output

Monthly cost · 30 days

Cheapest: $105; GPT-6 Luna
Priciest: $285; Gemini 3.1 Flash-Lite
Spread: 2.7×; priciest vs cheapest

	Per request		Per 1K users / mo
GPT-6 LunaCheapest	$0.00035	$105	$52.50
Gemini 3.1 Flash-Lite	$0.00095	$285	$143

Per 1K users assumesrequests per user per day.

Where the money is

If 60% of your traffic is simple enough for GPT-6 Luna, routing it there instead of Gemini 3.1 Flash-Lite saves about $108/month.

You're looking at $105–$285/month.

Most AI products I audit can cut that 30–60% with routing, caching and shorter prompts.

Get a cost-cutting audit

Cost at three traffic levels

Same request on both: 2,000 input tokens and 300 output tokens, no caching, no batch, 30-day month.

Monthly cost of GPT-6 Luna vs Gemini 3.1 Flash-Lite
Requests / day	GPT-6 Luna	Gemini 3.1 Flash-Lite	Difference
1,000	$10.50	$28.50	$18.00
10,000	$105	$285	$180
100,000	$1,050	$2,850	$1,800

By request type:

Cost per 1,000 calls by request type, GPT-6 Luna vs Gemini 3.1 Flash-Lite
Per 1K calls	GPT-6 Luna	Gemini 3.1 Flash-Lite
Classification or routing call	$0.0450	$0.1150
Support chat reply	$0.2750	$0.7500
RAG answer over your docs	$0.8000	$2.10
Long document summary	$4.50	$11.50

When to pick which

GPT-6 Luna is 2.5× cheaper on input tokens, which matters most for RAG and long prompts.
GPT-6 Luna is 3.0× cheaper on output tokens, which matters most for long answers, code generation and reasoning.
GPT-6 Luna has a published cached-input rate; this calculator bills Gemini 3.1 Flash-Lite's cached tokens at the full input rate.
Both offer 50% off for batch processing.
GPT-6 Luna has the larger context window (1.05M tokens vs 1.05M tokens).
GPT-6 Luna bills the whole request at a higher rate once input passes 272,000 tokens.

GPT-6 Luna: OpenAI's cheapest current model. Bulk tagging, extraction, routing and lightweight chat.

Gemini 3.1 Flash-Lite: Google's budget tier for high-volume text, image and video understanding.

Verdict

GPT-6 Luna wins on price

2.7× cheaper

On price alone, GPT-6 Luna wins: about 2.7× cheaper than Gemini 3.1 Flash-Lite for a typical request. Price is one input. Run both on 50 of your real prompts, compare the answers and the billed tokens, and route by difficulty if the quality gap only shows up on hard requests.

How the math works

Every provider bills input tokens (your prompt, system prompt and retrieved documents) and output tokens (the reply) separately, per million. Output is usually 4–5× the input price, so chatty apps are output-heavy and RAG apps are input-heavy.

cost per request = (fresh_in × input_price

+ cached_in × cached_price

+ out × output_price) / 1,000,000

× (1 − batched_share × batch_discount)

monthly = cost per request × requests per day × 30

Two adjustments are applied automatically. Introductory prices (currently on some Gemini models) are used until their end date. Long-prompt surcharges kick in when your average input crosses the provider's threshold: 272K tokens on current OpenAI models, 100K on Claude Haiku 5.5.

Not modelled: cache-write premiums, priority or fast tiers, regional surcharges, image and audio tokens, and reasoning tokens a model spends before answering (they bill as output, so add them to your output estimate if you use extended thinking).

Questions

Which is cheaper, GPT-6 Luna or Gemini 3.1 Flash-Lite?

For a typical request of 2,000 input and 300 output tokens, GPT-6 Luna is about 2.7× cheaper: $0.00035 per call on GPT-6 Luna vs $0.00095 on Gemini 3.1 Flash-Lite. At 10,000 requests a day that is $105 vs $285 a month.

Can I use both GPT-6 Luna and Gemini 3.1 Flash-Lite?

Yes, and many teams do. Put a thin routing layer in front of both: send the requests that need the stronger or larger-context model to it, and everything else to the cheaper one. Keep prompts provider-neutral so you can move traffic when prices change.

How often do OpenAI and Google change prices?

Often enough that a comparison older than a few months is suspect. The prices on this page were verified on 7 Nov 2026 from each provider's own documentation, linked in the Sources section.

Sources

All prices are list prices from each provider's own documentation, standard tier, in USD, last verified on 7 Nov 2026. Providers change prices often; if a number here disagrees with the source, the source wins.

GPT-6 Lunadevelopers.openai.com
Gemini 3.1 Flash-Liteai.google.dev

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