Which is more cost-effective, Gemini 1.5 Flash or Gemini 3.1 Flash-Lite?

Based on 1M input + 1M output tokens, Gemini 1.5 Flash costs $0.38/month versus Gemini 3.1 Flash-Lite at $1.75/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?

Gemini 1.5 Flash scores 72 in coding and 76 in reasoning benchmarks. Gemini 3.1 Flash-Lite scores 80 in coding and 81 in reasoning. See the full 5-category breakdown in the Benchmark Comparison section above.

What are the context window sizes of Gemini 1.5 Flash and Gemini 3.1 Flash-Lite?

Gemini 1.5 Flash supports a 1.0M-token context window while Gemini 3.1 Flash-Lite 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?

Gemini 1.5 Flash has a speed score of 99/100 and Gemini 3.1 Flash-Lite scores 98/100 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

Gemini 1.5 Flash vs Gemini 3.1 Flash-Lite

Model AGoogle

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

Model BGoogle

Gemini 3.1 Flash-Lite

Capability score (editorial)81/100

Cost / 1M Tokens: $0.63; 70% in · 30% out mix
Value Index (score÷cost): 133.6; Higher = better value

Speed: 98/100
Context: 1.0M
Tier: Fast Tier

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

Check the source

How we verify prices

In-depth analysis

Gemini 1.5 Flash vs Gemini 3.1 Flash-Lite: Detailed Comparison

Gemini 1.5 Flash is Google's lightweight-tier language model with a 1.0M-token context window, excelling at data extraction. Gemini 3.1 Flash-Lite from Google is a lightweight-tier model supporting 1.0M tokens in context, with standout performance in data extraction.

Gemini 3.1 Flash-Lite costs 4.4x what Gemini 1.5 Flash does for the same text. That is a steep premium, and it buys a 13-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. Gemini 1.5 Flash is priced at $0.08/M input tokens and $0.30/M output tokens. Gemini 3.1 Flash-Lite costs $0.25/M input and $1.50/M output.

On iOPTERA's editorial scores, Gemini 3.1 Flash-Lite leads with 80/100 for coding and 81/100 for reasoning, against Gemini 1.5 Flash's 72/100 and 76/100.

Capability breakdown

Across the five core benchmark categories, here is how Gemini 1.5 Flash and Gemini 3.1 Flash-Lite stack up head to head:

coding

Gemini 3.1 leads

reasoning

Gemini 3.1 leads

data extraction

Gemini 1.5 leads

creative tasks

Gemini 3.1 leads

vision/multimodal

Gemini 3.1 leads

Best model by task

coding: Gemini 3.1 Flash-Lite wins with 80/100
reasoning: Gemini 3.1 Flash-Lite wins with 81/100
data extraction: Gemini 1.5 Flash wins with 93/100
creative tasks: Gemini 3.1 Flash-Lite wins with 79/100
vision/multimodal: Gemini 3.1 Flash-Lite wins with 87/100

Estimated monthly cost at scale

For 10M + 2M tokens of text a month (counted the way OpenAI's tokenizer counts), Gemini 1.5 Flash runs about $1.30 while Gemini 3.1 Flash-Lite runs about $5.34 — Gemini 1.5 Flash saves roughly $4.04 (76%) every month.

What actually decides it

Both models come from Google, so they share a tokenizer, an API surface, and a billing account. Switching between them is a model-string change and nothing else — no new SDK, no re-tokenizing your prompts to re-estimate cost, no second vendor to onboard. That makes routing between them far cheaper to implement than a cross-vendor split.

These are the same lab's model at the same tier, 24 months apart — so this is an upgrade question, not a choice between alternatives. Gemini 3.1 Flash-Lite is the current entry; Gemini 1.5 Flash is here because plenty of production traffic still runs on it. If you are starting something new there is little reason to pick the older one, and if you are already on it the question is whether the migration cost is worth the gain.

Context is effectively a tie: 1.0M 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: Gemini 3.1 Flash-Lite 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.

Gemini 3.1 Flash-Lite is 4.4x 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	Gemini 1.5 Flash	Gemini 3.1 Flash-Lite
List price (input / output)	$0.075 / $0.30	$0.25 / $1.50
Cached input	—	$0.02510% of the input price
Batch API	—	50% off input and output
Long prompts	—	No surcharge across the 1.05M window
Input with 80% cache hits	—	$0.07

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 Google.

Capability scores

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

CategoryGemini 1.5Gemini 3.1Winner

Coding

Reasoning

Extraction

Creative

Vision

Gemini 1.5 Flash: 1 wins

Gemini 3.1 Flash-Lite: 4 wins

Gemini 3.1 Flash-Lite leads overall

Speed Score

99/100vs98/100

GeminiGemini

Context Window

1000Kvs1049K

GeminiGemini

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

Gemini 1.5 Flash: $0.03
Gemini 3.1 Flash-Lite: $0.10

Business email

One typical email (~200 words)

~270 tokens

Gemini 1.5 Flash: $1.94
Gemini 3.1 Flash-Lite: $6.55

Code file

50-line Python script

~400 tokens

Gemini 1.5 Flash: $2.88
Gemini 3.1 Flash-Lite: $9.70

Prices shown are for 100,000 runs of each workload — one run costs a fraction of a cent on both Gemini 1.5 Flash and Gemini 3.1 Flash-Lite, 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%

Cheaper

Gemini 1.5 Flash

$4.10/mo

$49.25/yr

$0.075/M input$0.30/M output

Gemini 3.1 Flash-Lite

$18.19/mo

$218.25/yr

$0.25/M input$1.50/M output

Annual Savings

$169.00 saved per year

Gemini 1.5 Flash cheaper · $14.08/mo

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