API cost decision in 10 seconds

🔥DeepSeek V4 Pro vs 🔥Step 3.5 Flash

Pick Step 3.5 Flash for lower cost; pick DeepSeek V4 Pro only if the larger context window matters more.

Pricing data updated: 2026-05-13T16:32:23Z Prices normalized to USD per 1M tokens Sample workload: 1M input + 500K output

Budget verdict

Pick Step 3.5 Flash for lower cost; pick DeepSeek V4 Pro 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 $0.87 for DeepSeek V4 Pro, saving $0.62 (71.3% lower).

Cost-first pickStep 3.5 Flash

Context-first pickDeepSeek V4 Pro

Sample savings$0.6271.3%

10x traffic gap$6.2

DeepSeek V4 Pro has more context, but Step 3.5 Flash saves $0.62 on the standard workload. At 10x that traffic, the same price gap is about $6.2. Use the calculator below to replace the sample workload with your own token volume.

Cheaper input Step 3.5 Flash $0.435 vs $0.1 / 1M

Step 3.5 Flash is $0.33 cheaper per 1M input tokens (77% lower; 4.35x difference).

Cheaper output Step 3.5 Flash $0.87 vs $0.3 / 1M

Step 3.5 Flash is $0.57 cheaper per 1M output tokens (65.5% lower; 2.9x difference).

Larger context DeepSeek V4 Pro 1.05M vs 262.14K

DeepSeek V4 Pro has 786.43K more context (4x larger).

Sample workload Step 3.5 Flash $0.87 vs $0.25

Step 3.5 Flash is $0.62 cheaper on the standard workload (71.3% lower).

Estimate your workload cost

Your Workload Cost

Prices are normalized to USD per 1M tokens.

Monthly input tokens Monthly output tokens

DeepSeek V4 Pro 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; DeepSeek V4 Pro 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 $0.87 for DeepSeek V4 Pro and $0.25 for Step 3.5 Flash.

Best Fit

Choose DeepSeek V4 Pro 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 $0.87 for DeepSeek V4 Pro, saving $0.62 (71.3% lower).
Step 3.5 Flash is $0.62 cheaper on the standard workload (71.3% lower).
Step 3.5 Flash is $0.33 cheaper per 1M input tokens (77% lower; 4.35x difference).
Step 3.5 Flash is $0.57 cheaper per 1M output tokens (65.5% lower; 2.9x difference).
DeepSeek V4 Pro has 786.43K more context (4x larger).

Head-to-Head Specs

Feature	🔥DeepSeek V4 Pro (DeepSeek)	🔥Step 3.5 Flash (StepFun)
Input Price prompt tokens per 1M	$0.435	$0.1
Completion Price per 1M tokens	$0.87	$0.3
Sample Workload Cost 1M input + 500K output	$0.87	$0.25
Context Window	1.05M	262.14K
Release Date	2026-04-24	2026-01-29
Popularity Rank current rank	#8	#15

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 $0.87 for DeepSeek V4 Pro, saving $0.62 (71.3% 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	DeepSeek V4 Pro	A larger context window leaves more room for retrieved passages, conversation history, or source files.

Related Alternatives

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Provider catalogs

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DeepSeek catalog

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StepFun catalog

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DeepSeek V4 Pro

DeepSeek V4 Pro is a large-scale Mixture-of-Experts model from DeepSeek with 1.6T total parameters and 49B activated parameters, supporting a 1M-token context window. It is designed for advanced reasoning, coding,...

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....