DeepSeek V4 Pro vs GPT-5.6 Luna
GPT-5.6 Luna is the cheaper of the two, at 1.2x less on a blended 3:1 input-to-output rate. DeepSeek V4 Pro runs $0.435 in / $0.87 out per 1M tokens; GPT-5.6 Luna runs $0.20 in / $1.20 out.
On the heaviest scenario below, that gap is $437.00 a month ($5,244 a year) for identical volume. Verified 2026-08-16.
Side by side
| DeepSeek V4 Pro | GPT-5.6 Luna | |
|---|---|---|
| Provider | DeepSeek | OpenAI |
| Input per 1M tokens | $0.435 | $0.20 |
| Output per 1M tokens | $0.87 | $1.20 |
| Cached input per 1M | $0.003625 | $0.02 |
| Batch discount | Not offered | Not offered |
| Output-to-input ratio | 2.0x | 6.0x |
| Blended per 1M (3:1) | $0.544 | $0.450 |
What each costs on the same workload
Rate cards are hard to compare directly because the input:output mix changes the answer. These four scenarios hold the workload fixed and vary only the model, with no caching or batch discount applied to either side.
| Workload | DeepSeek V4 Pro | GPT-5.6 Luna | Monthly difference | Cheaper |
|---|---|---|---|---|
| Support chatbot 50,000 conversations/month at 3K input and 500 output tokens each | $87.00 | $60.00 | $27.00 | GPT-5.6 Luna |
| RAG document search 200,000 queries/month at 6K retrieved-context input and 400 output tokens | $591.60 | $336.00 | $255.60 | GPT-5.6 Luna |
| Coding agent 5,000 runs/month at 60K input and 8K output tokens per run | $165.30 | $108.00 | $57.30 | GPT-5.6 Luna |
| Bulk classification 5,000,000 items/month at 400 input and 20 output tokens each | $957.00 | $520.00 | $437.00 | GPT-5.6 Luna |
Which should you actually pick?
There is no single winner here, and that is the useful finding. GPT-5.6 Luna has the cheaper input rate ($0.20 vs $0.435), while DeepSeek V4 Pro has the cheaper output rate ($0.87 vs $1.20). Prompt-heavy workloads such as retrieval-augmented search, long system prompts, and document analysis lean toward GPT-5.6 Luna. Generation-heavy workloads such as long-form writing, code generation, and agent loops that produce a lot of tokens lean toward DeepSeek V4 Pro.
Discounts can also flip the arithmetic. Prompt caching is the bigger lever of the two for anything that resends a stable prefix: see the prompt caching savings calculator.
DeepSeek V4 Pro vs GPT-5.6 Luna: common questions
Is DeepSeek V4 Pro or GPT-5.6 Luna cheaper?
GPT-5.6 Luna is cheaper overall, at 1.2x less on a blended 3:1 input-to-output rate ($0.450 vs $0.544 per 1M blended tokens). It is not a clean sweep though: GPT-5.6 Luna has the cheaper input rate while DeepSeek V4 Pro has the cheaper output rate, so a generation-heavy workload can flip the answer.
What is the price difference between DeepSeek V4 Pro and GPT-5.6 Luna on a real workload?
On the bulk classification scenario (5,000,000 items/month at 400 input and 20 output tokens each), DeepSeek V4 Pro costs $957.00 a month and GPT-5.6 Luna costs $520.00. That is a difference of $437.00 a month, or $5,244 a year, for the same volume of work.
Does DeepSeek V4 Pro or GPT-5.6 Luna have better discounts?
DeepSeek V4 Pro offers cached input at $0.003625. GPT-5.6 Luna offers cached input at $0.02. On cache-heavy or latency-tolerant workloads these can matter more than the headline rate.
Should I switch from DeepSeek V4 Pro to GPT-5.6 Luna?
Only if the cheaper model actually does the job. Price is the easy half of the decision; the hard half is whether output quality holds on your task. Run both against a sample of real traffic, then use the model switching savings calculator to put a number on the annual difference before committing.