API cost decision in 10 seconds

🔥Gemini 3.1 Pro Preview vs 🔥Step 3.5 Flash

Pick Step 3.5 Flash for lower cost; pick Gemini 3.1 Pro Preview only if the larger context window matters more.

Pricing data updated: 2026-05-15T02:08:14Z Prices normalized to USD per 1M tokens Sample workload: 1M input + 500K output

Budget verdict

Pick Step 3.5 Flash for lower cost; pick Gemini 3.1 Pro Preview only if the larger context window matters more.

On the standard 1M input plus 500K output workload, Step 3.5 Flash is estimated at $0.25 vs $8 for Gemini 3.1 Pro Preview, saving $7.75 (96.9% lower).

Cost-first pickStep 3.5 Flash

Context-first pickGemini 3.1 Pro Preview

Sample savings$7.7596.9%

10x traffic gap$77.5

Gemini 3.1 Pro Preview has more context, but Step 3.5 Flash saves $7.75 on the standard workload. At 10x that traffic, the same price gap is about $77.5. Use the calculator below to replace the sample workload with your own token volume.

Cheaper input Step 3.5 Flash $2 vs $0.1 / 1M

Step 3.5 Flash is $1.9 cheaper per 1M input tokens (95% lower; 20x difference).

Cheaper output Step 3.5 Flash $12 vs $0.3 / 1M

Step 3.5 Flash is $11.7 cheaper per 1M output tokens (97.5% lower; 40x difference).

Larger context Gemini 3.1 Pro Preview 1.05M vs 262.14K

Gemini 3.1 Pro Preview has 786.43K more context (4x larger).

Sample workload Step 3.5 Flash $8 vs $0.25

Step 3.5 Flash is $7.75 cheaper on the standard workload (96.9% lower).

Estimate your workload cost

Your Workload Cost

Prices are normalized to USD per 1M tokens.

Monthly input tokens Monthly output tokens

Gemini 3.1 Pro Preview Calculating… Estimated API cost

Step 3.5 Flash 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

Step 3.5 Flash has the lower input price; Step 3.5 Flash has the lower output price; Gemini 3.1 Pro Preview offers the larger context window. For the 1M input plus 500K output sample, Step 3.5 Flash is cheaper for the standard workload.

For a 1M input token plus 500K output token workload, the estimated API cost is $8 for Gemini 3.1 Pro Preview and $0.25 for Step 3.5 Flash.

Best Fit

Choose Gemini 3.1 Pro Preview when you care most about larger context window.

Choose Step 3.5 Flash when you care most about lower input-token price, and lower output-token price.

Decision Notes

On the standard 1M input plus 500K output workload, Step 3.5 Flash is estimated at $0.25 vs $8 for Gemini 3.1 Pro Preview, saving $7.75 (96.9% lower).
Step 3.5 Flash is $7.75 cheaper on the standard workload (96.9% lower).
Step 3.5 Flash is $1.9 cheaper per 1M input tokens (95% lower; 20x difference).
Step 3.5 Flash is $11.7 cheaper per 1M output tokens (97.5% lower; 40x difference).
Gemini 3.1 Pro Preview has 786.43K more context (4x larger).

Head-to-Head Specs

Feature	🔥Gemini 3.1 Pro Preview (Google)	🔥Step 3.5 Flash (StepFun)
Input Price prompt tokens per 1M	$2	$0.1
Completion Price per 1M tokens	$12	$0.3
Sample Workload Cost 1M input + 500K output	$8	$0.25
Context Window	1.05M	262.14K
Release Date	2026-02-19	2026-01-29
Popularity Rank current rank	#10	#11

Use-Case Decision Matrix

Use case	Better pick	Why
Budget-constrained production	Step 3.5 Flash	On the standard 1M input plus 500K output workload, Step 3.5 Flash is estimated at $0.25 vs $8 for Gemini 3.1 Pro Preview, saving $7.75 (96.9% lower).
High-volume input processing	Step 3.5 Flash	Lower prompt-token price matters most when prompts, retrieved passages, or documents dominate the bill.
Long responses and chatbots	Step 3.5 Flash	Lower output-token price matters most when assistants generate many completion tokens.
RAG or long-document work	Gemini 3.1 Pro Preview	A larger context window leaves more room for retrieved passages, conversation history, or source files.

Related Alternatives

Same-provider lower-cost swaps

Gemma 4 26B A4B (free) can replace Gemini 3.1 Pro Preview when lower sample workload cost matters most: $0.
Gemma 4 31B (free) can replace Gemini 3.1 Pro Preview when lower sample workload cost matters most: $0.
Lyria 3 Pro Preview can replace Gemini 3.1 Pro Preview when lower sample workload cost matters most: $0.
Lyria 3 Clip Preview can replace Gemini 3.1 Pro Preview when lower sample workload cost matters most: $0.

Larger context near this budget

Grok 4.1 Fast offers 2M context with $0.45 sample workload cost.
Grok 4.20 Multi-Agent offers 2M context with $5 sample workload cost.
Grok 4.20 offers 2M context with $2.5 sample workload cost.
Grok 4 Fast offers 2M context with $0.45 sample workload cost.

Popular competitors

Hy3 preview · Tencent · #1
Claude Opus 4.7 · Anthropic · #2
Claude Sonnet 4.6 · Anthropic · #3
DeepSeek V4 Flash · DeepSeek · #4

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Google catalog

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StepFun catalog

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Gemini 3.1 Pro Preview

Gemini 3.1 Pro Preview is Google’s frontier reasoning model, delivering enhanced software engineering performance, improved agentic reliability, and more efficient token usage across complex workflows. Building on the multimodal foundation...

Step 3.5 Flash

Step 3.5 Flash is StepFun's most capable open-source foundation model. Built on a sparse Mixture of Experts (MoE) architecture, it selectively activates only 11B of its 196B parameters per token....