API cost decision in 10 seconds

GPT-5.6 Luna Pro (batch) vs Gemini 3.5 Flash (batch)

Pick GPT-5.6 Luna Pro (batch) when budget and context both matter.

Page updated: 2026-08-06T14:08:16Z Data confirmed: 2026-08-23T12:07:48Z Prices normalized to USD per 1M tokens Sample workload: 1M input + 500K output

Budget verdict

Pick GPT-5.6 Luna Pro (batch) when budget and context both matter.

On the standard 1M input plus 500K output workload, GPT-5.6 Luna Pro (batch) is estimated at $0.4 vs $3 for Gemini 3.5 Flash (batch), saving $2.6 (86.7% lower).

Cost-first pickGPT-5.6 Luna Pro (batch)

Context-first pickGPT-5.6 Luna Pro (batch)

Sample savings$2.686.7%

10x traffic gap$26

GPT-5.6 Luna Pro (batch) is cheaper on the standard workload and also has the larger context window. At 10x that traffic, the same price gap is about $26. Use the calculator below to replace the sample workload with your own token volume.

Cost sensitivity

Workload Sensitivity

Same prices, different token mixes.

GPT-5.6 Luna Pro (batch) stays cheaper across input-heavy, balanced, and output-heavy sample workloads.

Workload shape	Token mix	Better pick	GPT-5.6 Luna Pro (batch)	Gemini 3.5 Flash (batch)
Input-heavy / RAG	5M input + 500K output	GPT-5.6 Luna Pro (batch)	$0.8	$6
Balanced workload	1M input + 1M output	GPT-5.6 Luna Pro (batch)	$0.7	$5.25
Output-heavy chatbot	1M input + 5M output	GPT-5.6 Luna Pro (batch)	$3.1	$23.25

Cheaper input GPT-5.6 Luna Pro (batch) $0.1 vs $0.75 / 1M

GPT-5.6 Luna Pro (batch) is $0.65 cheaper per 1M input tokens (86.7% lower; 7.5x difference).

Cheaper output GPT-5.6 Luna Pro (batch) $0.6 vs $4.5 / 1M

GPT-5.6 Luna Pro (batch) is $3.9 cheaper per 1M output tokens (86.7% lower; 7.5x difference).

Larger context GPT-5.6 Luna Pro (batch) 1.05M vs 1.05M

GPT-5.6 Luna Pro (batch) has 1.42K more context (1x larger).

Sample workload GPT-5.6 Luna Pro (batch) $0.4 vs $3

GPT-5.6 Luna Pro (batch) is $2.6 cheaper on the standard workload (86.7% lower).

Estimate your workload cost

Your Workload Cost

Prices are normalized to USD per 1M tokens.

Monthly input tokens Monthly output tokens

GPT-5.6 Luna Pro (batch) Calculating… Estimated API cost

Gemini 3.5 Flash (batch) Calculating… Estimated API cost

Cheaper for this workload Calculating… Difference: calculating…

This estimate uses normalized public API pricing per 1M tokens. It is a planning aid, not a billing quote. Verify provider pricing, limits, and terms before production use.

Quick Decision

Verdict

GPT-5.6 Luna Pro (batch) has the lower input price; GPT-5.6 Luna Pro (batch) has the lower output price; GPT-5.6 Luna Pro (batch) offers the larger context window. For the 1M input plus 500K output sample, GPT-5.6 Luna Pro (batch) is cheaper for the standard workload.

For a 1M input token plus 500K output token workload, the estimated API cost is $0.4 for GPT-5.6 Luna Pro (batch) and $3 for Gemini 3.5 Flash (batch).

Best Fit

Choose GPT-5.6 Luna Pro (batch) when you care most about lower input-token price, lower output-token price, and larger context window.

Choose Gemini 3.5 Flash (batch) when its provider, model quality, latency, or availability is more important than the numeric price/context winner.

Decision Notes

On the standard 1M input plus 500K output workload, GPT-5.6 Luna Pro (batch) is estimated at $0.4 vs $3 for Gemini 3.5 Flash (batch), saving $2.6 (86.7% lower).
GPT-5.6 Luna Pro (batch) is $2.6 cheaper on the standard workload (86.7% lower).
GPT-5.6 Luna Pro (batch) is $0.65 cheaper per 1M input tokens (86.7% lower; 7.5x difference).
GPT-5.6 Luna Pro (batch) is $3.9 cheaper per 1M output tokens (86.7% lower; 7.5x difference).
GPT-5.6 Luna Pro (batch) has 1.42K more context (1x larger).

Head-to-Head Specs

Feature	GPT-5.6 Luna Pro (batch) (OpenAI)	Gemini 3.5 Flash (batch) (Google)
Input Price prompt tokens per 1M	$0.1	$0.75
Completion Price per 1M tokens	$0.6	$4.5
Sample Workload Cost 1M input + 500K output	$0.4	$3
Context Window	1.05M	1.05M
Release Date	2026-07-09	2026-05-19

Use-Case Decision Matrix

Use case	Better pick	Why
Budget-constrained production	GPT-5.6 Luna Pro (batch)	On the standard 1M input plus 500K output workload, GPT-5.6 Luna Pro (batch) is estimated at $0.4 vs $3 for Gemini 3.5 Flash (batch), saving $2.6 (86.7% lower).
High-volume input processing	GPT-5.6 Luna Pro (batch)	Lower prompt-token price matters most when prompts, retrieved passages, or documents dominate the bill.
Long responses and chatbots	GPT-5.6 Luna Pro (batch)	Lower output-token price matters most when assistants generate many completion tokens.
RAG or long-document work	GPT-5.6 Luna Pro (batch)	A larger context window leaves more room for retrieved passages, conversation history, or source files.

Related Alternatives

Same-provider lower-cost swaps

gpt-oss-120b (free) can replace GPT-5.6 Luna Pro (batch) when lower sample workload cost matters most: $0.
gpt-oss-20b (free) can replace GPT-5.6 Luna Pro (batch) when lower sample workload cost matters most: $0.
gpt-oss-20b can replace GPT-5.6 Luna Pro (batch) when lower sample workload cost matters most: $0.1.
gpt-oss-120b can replace GPT-5.6 Luna Pro (batch) when lower sample workload cost matters most: $0.12.

Larger context near this budget

Grok 4.20 Multi-Agent offers 2M context with $2.5 sample workload cost.
Grok 4.20 offers 2M context with $2.5 sample workload cost.
DeepSeek V4 Flash 0731 offers 1.31M context with $0.17 sample workload cost.
DeepSeek V4 Flash Latest offers 1.31M context with $0.11 sample workload cost.

Popular competitors

DeepSeek V4 Flash 0731 · DeepSeek · #1
MiMo-V2.5 · Xiaomi · #2
Hy3 · Tencent · #3
Ox Alpha · stealth · #4

Cheaper alternatives

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Larger context alternatives

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Provider catalogs

Compare models within provider hubs before choosing a final API vendor.

Open provider hubs

OpenAI catalog

Review all tracked OpenAI models before deciding whether this matchup is the right shortlist.

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Google catalog

Check other Google models with comparable pricing, context, or release timing.

Open Google models

GPT-5.6 Luna Pro (batch)

GPT-5.6 Luna Pro is the same underlying model as [GPT-5.6 Luna](https://openrouter.ai/openai/gpt-5.6-luna), served with `reasoning.mode` set to `pro` for higher-quality responses on complex tasks. Learn more in OpenAI's docs: https://developers.openai.com/api/docs/guides/reasoning#reasoning-mode

Gemini 3.5 Flash (batch)

Gemini 3.5 Flash is Google's high-efficiency multimodal model, bringing near-Pro level coding and reasoning at Flash-tier cost and speed. It is highly optimized for coding proficiency and parallel agentic execution...