Which is more cost-effective, GPT-5.6 Luna or Gemini 1.5 Flash?

Based on 1M input + 1M output tokens, GPT-5.6 Luna costs $1.40/month versus Gemini 1.5 Flash at $0.38/month. The cheaper option depends on your token volume and prompt-to-completion ratio. Use the interactive calculator on this page to enter your exact usage.

How accurate is this cost comparison?

List prices come from each provider's own pricing page and every model page shows when they were last verified. The capability scores are iOPTERA's editorial composites — informed by public benchmarks, not benchmark results themselves; the methodology page explains how they are set.

Which model scores higher on benchmarks?

GPT-5.6 Luna scores 84 in coding and 85 in reasoning benchmarks. Gemini 1.5 Flash scores 72 in coding and 76 in reasoning. See the full 5-category breakdown in the Benchmark Comparison section above.

What are the context window sizes of GPT-5.6 Luna and Gemini 1.5 Flash?

GPT-5.6 Luna supports a 1.1M-token context window while Gemini 1.5 Flash supports 1.0M tokens. A larger context window lets you process more text in a single API call.

Which model is faster for real-time applications?

GPT-5.6 Luna has a speed score of 98/100 and Gemini 1.5 Flash scores 99/100 on our latency benchmark. For interactive chatbots and low-latency tasks, the higher speed score is preferable.

Can I calculate costs for my specific token volume?

Yes. Use the interactive cost calculator on this page. Enter your monthly token volume and adjust the prompt-to-completion ratio. You can also use presets for common scenarios like Customer Support Bots (~30M tokens/month) or Document Summarizers (~15M tokens/month).

Cost and performance comparison

GPT-5.6 Luna vs Gemini 1.5 Flash

Model AOpenAI

GPT-5.6 Luna

Capability score (editorial)85/100

Cost / 1M Tokens: $0.50; 70% in · 30% out mix
Value Index (score÷cost): 170.0; Higher = better value

Speed: 98/100
Context: 1.1M
Tier: Fast Tier

List price from the OpenAI pricing page, verified October 12, 2026.

Check the source

How we verify prices

Model BGoogle

Gemini 1.5 Flash

Capability score (editorial)76/100

Cost / 1M Tokens: $0.14; 70% in · 30% out mix
Value Index (score÷cost): 555.6; Higher = better value

Speed: 99/100
Context: 1.0M
Tier: Fast Tier

Last list price before the model was retired.

How we verify prices

In-depth analysis

GPT-5.6 Luna vs Gemini 1.5 Flash: Detailed Comparison

GPT-5.6 Luna is OpenAI's lightweight-tier language model with a 1.1M-token context window, excelling at data extraction. Gemini 1.5 Flash from Google is a lightweight-tier model supporting 1.0M tokens in context, with standout performance in data extraction.

GPT-5.6 Luna costs 3.7x what Gemini 1.5 Flash does for the same text. That is a steep premium, and it buys a 21-point lead on combined coding and reasoning. Whether that trade is worth it depends entirely on how much of your traffic actually needs the harder model — for most workloads the honest answer is a small fraction of it, which is an argument for routing rather than for picking one. GPT-5.6 Luna is priced at $0.20/M input tokens and $1.20/M output tokens. Gemini 1.5 Flash costs $0.08/M input and $0.30/M output.

On iOPTERA's editorial scores, GPT-5.6 Luna leads with 84/100 for coding and 85/100 for reasoning, against Gemini 1.5 Flash's 72/100 and 76/100.

Capability breakdown

Across the five core benchmark categories, here is how GPT-5.6 Luna and Gemini 1.5 Flash stack up head to head:

coding

GPT-5.6 Luna leads

reasoning

GPT-5.6 Luna leads

data extraction

Gemini 1.5 leads

creative tasks

GPT-5.6 Luna leads

vision/multimodal

Tie

Best model by task

coding: GPT-5.6 Luna wins with 84/100
reasoning: GPT-5.6 Luna wins with 85/100
data extraction: Gemini 1.5 Flash wins with 93/100
creative tasks: GPT-5.6 Luna wins with 84/100

Estimated monthly cost at scale

For 10M + 2M tokens of text a month (counted the way OpenAI's tokenizer counts), GPT-5.6 Luna runs about $4.40 while Gemini 1.5 Flash runs about $1.30 — Gemini 1.5 Flash saves roughly $3.10 (71%) every month.

What actually decides it

GPT-5.6 Luna and Gemini 1.5 Flash come from different labs, which means different tokenizers, different API shapes, and a second vendor relationship. The same English text does not produce the same token count on both, so a price-per-million comparison understates the difference — measure your own prompts on each before treating the headline rates as the full story.

GPT-5.6 Luna and Gemini 1.5 Flash are 26 months apart, which is more than one generation in this market. Benchmark comparisons across that gap flatter the older model: it was measured against the evaluations that existed at the time. Treat Gemini 1.5 Flash's scores as a floor for what it does well and be sceptical of a close-looking result.

Context is effectively a tie: 1.1M against 1.0M. Neither model unlocks a document size the other cannot handle, so this axis should not enter the decision. If you were hoping context would break the tie for you, it will not.

Throughput is close enough to ignore — 99/100 versus 98/100. Neither model will feel noticeably quicker in an interactive product, so latency is not a reason to choose between them.

One practical asymmetry: GPT-5.6 Luna offers a batch API at 50% off standard rates, and Gemini 1.5 Flash does not. For anything that does not need an answer immediately — nightly enrichment, backfills, evaluation runs — that discount can be worth more than the difference in list price, and it is easy to overlook when comparing headline rates.

GPT-5.6 Luna is 3.7x the price of Gemini 1.5 Flash. Reserve it for the requests that actually need it and route the rest to Gemini 1.5 Flash — that hybrid beats either model used alone on cost per useful answer.

What you actually pay

The list price is only the start. Prompt caching, batch processing and long prompts change the bill, and each provider sets them differently. Prices per 1M tokens.

Pricing terms beyond the list price, per 1M tokens
Pricing term	GPT-5.6 Luna	Gemini 1.5 Flash
List price (input / output)	$0.20 / $1.20	$0.075 / $0.30
Cached input	$0.0210% of the input price	—
Batch API	50% off input and output	—
Long prompts	Over 272K tokens: $0.40 / $1.80	—
Input with 80% cache hits	$0.056	—

The last row assumes 80% of input tokens are read from the cache, as in a chat app that re-sends a long system prompt or RAG over the same documents. Cache-write and storage charges are not included.

Gemini also bills cache storage by the hour.

Checked on October 8, 2026 against the pricing pages of OpenAI, Google.

Capability scores

iOPTERA editorial scores across 5 categories — informed by public benchmarks, not measured by us

CategoryGPT-5.6 LunaGemini 1.5Winner

Coding

Reasoning

Extraction

Creative

Vision

Tied

GPT-5.6 Luna: 3 wins

Gemini 1.5 Flash: 1 wins

GPT-5.6 Luna leads overall

Speed Score

98/100vs99/100

GPT-5.6Gemini

Context Window

1050Kvs1000K

GPT-5.6Gemini

What Is a Token?

Models don't read words — they process tokens.

A token is roughly 4 characters of English text (~¾ of a word). Your API bill is priced per million tokens — understanding this directly reduces your costs.

Short phrase

"Hello, world!"

4 tokens

GPT-5.6 Luna: $0.08
Gemini 1.5 Flash: $0.03

Business email

One typical email (~200 words)

~270 tokens

GPT-5.6 Luna: $5.40
Gemini 1.5 Flash: $1.94

Code file

50-line Python script

~400 tokens

GPT-5.6 Luna: $8.00
Gemini 1.5 Flash: $2.88

Prices shown are for 100,000 runs of each workload — one run costs a fraction of a cent on both GPT-5.6 Luna and Gemini 1.5 Flash, so the number only becomes meaningful at production volume. Input tokens only; add your output volume in the calculator below.

How to check your token usage

response.usage.total_tokens

Every API response includes a usage object. Sum total_tokens across all calls to get your monthly figure, then use the calculator below.

Your Cost Calculator

Enter your actual monthly token usage to see real savings

Quick Presets

Monthly Token Volume

30M tokens

Prompt / Completion Split

Prompt 70%Completion 30%

GPT-5.6 Luna

$15.00/mo

$180.00/yr

$0.20/M input$1.20/M output

Cheaper

Gemini 1.5 Flash

$4.10/mo

$49.25/yr

$0.075/M input$0.30/M output

Annual Savings

$130.75 saved per year

Gemini 1.5 Flash cheaper · $10.90/mo

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