Is GPT-5.6 Luna or Gemini 2.5 Flash-Lite cheaper?

Gemini 2.5 Flash-Lite is cheaper on all three of the workload shapes tested. On a RAG workload of 12k input and 700 output tokens at 50,000 requests per month with 60% caching, GPT-5.6 Luna costs $97.20 per month and Gemini 2.5 Flash-Lite costs $41.60. Headline rates are $0.2/$1.2 versus $0.1/$0.4 per million input/output tokens.

GPT-5.6 Luna vs Gemini 2.5 Flash-Lite

Gemini 2.5 Flash-Lite is the cheaper of the two across every workload shape tested below. Headline rates are $0.2 in / $1.2 out for GPT-5.6 Luna versus $0.1 in / $0.4 out for Gemini 2.5 Flash-Lite, per million tokens.

Real monthly cost, three workloads

Workload	GPT-5.6 Luna	Gemini 2.5 Flash-Lite	Cheaper
Support chatbot 1.5k in / 400 out · 100k req/mo · 30% cached	$69.90	$26.95	Gemini 2.5 Flash-Lite (2.6× cheaper)
RAG / doc Q&A 12k in / 700 out · 50k req/mo · 60% cached	$97.20	$41.60	Gemini 2.5 Flash-Lite (2.3× cheaper)
Coding agent 25k in / 2.5k out · 20k req/mo · 80% cached	$88.00	$34.00	Gemini 2.5 Flash-Lite (2.6× cheaper)

Costs include prompt caching at the stated hit rate and per-model tokenizer correction. Adjust for your own traffic →

Specifications side by side

	GPT-5.6 Luna	Gemini 2.5 Flash-Lite
Provider	OpenAI	Google
Input / M tokens	$0.2	$0.1
Output / M tokens	$1.2	$0.4
Cached input	$0.02	$0.01
Context window	1050K	—
Batch discount	−50%	−50%
Tokenizer factor	×1	×1
Min prefix to cache	—	—
Announced retirement	—	—

Which should you pick?

On cost alone, Gemini 2.5 Flash-Lite wins every workload shape above.

Full detail: GPT-5.6 Luna · Gemini 2.5 Flash-Lite

All figures verified 2026-08-18 against official provider documentation. Fields a provider does not publish are shown as “—” rather than estimated.