Gemini 3.5 Flash vs DeepSeek V4: API Price, Agents, and When to Use Each
Compare Gemini 3.5 Flash with DeepSeek V4 Flash and V4 Pro for 2026 API pricing, cached input, context windows, multimodal support, and agent routing.
Gemini 3.5 Flash and DeepSeek V4 solve different problems. Gemini 3.5 Flash is Google’s stable premium Flash route for multimodal agent workflows. DeepSeek V4 Flash and V4 Pro are cost-first text and agent models with extremely low cached-input pricing.
If your workload is mostly text, DeepSeek V4 is the cheaper default. If your workload needs Google ecosystem fit, multimodal inputs, search grounding, Maps grounding, URL context, Batch/Flex routing, or AI Studio workflow support, Gemini 3.5 Flash earns its premium.
Price Snapshot
| Model | Input / 1M | Cached Input / 1M | Output / 1M | Context | Max Output |
|---|---|---|---|---|---|
| Gemini 3.5 Flash | $1.50 | $0.15 | $9.00 | 1,048,576 | 65,536 |
| DeepSeek V4 Flash | $0.14 | $0.0028 | $0.28 | 1M | 384K |
| DeepSeek V4 Pro | $0.435 | $0.003625 | $0.87 | 1M | 384K |
At standard prices, Gemini 3.5 Flash costs about 10.7x more than DeepSeek V4 Flash on input and about 32x more on output. Compared with DeepSeek V4 Pro, Gemini 3.5 Flash is about 3.4x more expensive on input and about 10.3x more expensive on output.
Monthly Cost Examples
Assume standard interactive pricing and no cache hits.
| Daily usage | Gemini 3.5 Flash | DeepSeek V4 Flash | DeepSeek V4 Pro |
|---|---|---|---|
| 100K input + 50K output | $18.00/mo | $0.84/mo | $2.61/mo |
| 1M input + 500K output | $180.00/mo | $8.40/mo | $26.10/mo |
| 10M input + 5M output | $1,800/mo | $84/mo | $261/mo |
For repeated system prompts, repository context, documents, or instructions, DeepSeek’s cached input gap is even larger: $0.0028/M for V4 Flash and $0.003625/M for V4 Pro, versus $0.15/M for Gemini 3.5 Flash.
Capability Comparison
| Area | Gemini 3.5 Flash | DeepSeek V4 Flash / Pro |
|---|---|---|
| Input types | Text, image, video, audio, PDF | Text-focused API |
| Output | Text | Text |
| Function calling | Supported | Supported |
| Structured output | Supported | Supported |
| Context | 1,048,576 input tokens | 1M |
| Max output | 65,536 | 384K |
| Search grounding | Supported | Not the native advantage |
| Google Maps grounding | Supported | Not applicable |
| Batch/Flex options | Supported | Provider-specific API model |
| Best cost profile | Multimodal premium Flash | High-volume text and cached context |
Which Should You Use?
Choose Gemini 3.5 Flash when:
- Your agent needs image, video, audio, or PDF input.
- You need Google Search grounding, Maps grounding, URL context, or AI Studio workflow support.
- You want a stable Google Flash model for coding loops and multi-step agent workflows.
- Batch, Flex, Priority inference, or Google Cloud integration matters operationally.
Choose DeepSeek V4 Flash when:
- Most requests are text classification, extraction, summarization, formatting, or tool-calling.
- You need the lowest practical output price.
- You send repeated instructions, repository context, or documents and can benefit from cached input.
- Chinese and bilingual workloads are common.
Choose DeepSeek V4 Pro when:
- V4 Flash is too weak for a subset of requests, but GPT/Claude/Gemini premium pricing is hard to justify.
- You want the stronger DeepSeek V4 route while keeping output cost below $1/M.
- You can route only hard requests to Pro and keep easy requests on V4 Flash.
Practical Routing Pattern
For a product with mixed text and multimodal traffic:
- Route simple text tasks to DeepSeek V4 Flash.
- Route harder text reasoning to DeepSeek V4 Pro.
- Route image, video, audio, PDF, search-grounded, or Google ecosystem tasks to Gemini 3.5 Flash.
- Use cached input for repeated prompt blocks and long shared context.
- Use the AI Model Pricing Calculator to test your actual input/output ratio before changing production routing.
Bottom Line
DeepSeek V4 is the clear price winner for text agents. Gemini 3.5 Flash is the better fit when the workload needs multimodal inputs, search or Maps grounding, Google tooling, or a stable Google premium Flash route.
The cleanest architecture is not choosing one globally. Use DeepSeek V4 Flash as the default text route, DeepSeek V4 Pro for harder text requests, and Gemini 3.5 Flash only where its multimodal and Google-native capabilities matter.
Official sources checked: Google Gemini API pricing, Gemini 3.5 Flash model docs, and DeepSeek API pricing.
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