DeepSeek V4 Pro vs GPT-5.6 Sol: The 34x Price Gap, One Month Later

DeepSeek V4 Pro was released on August 13, 2026, and Open​AI's GPT-5.6 Sol came out of its July 9 API general availability at the flagship tier that costs about thirty-four times as much to generate from. A month on, that gap still frames the whole decision — GPT-5.6 Sol at $4.00 per million input tokens and $20.00 per million output tokens against DeepSeek V4 Pro's $1.32/$3.96 peak (and $0.66/$1.98 off-peak) — but two September events have reshaped what the comparison actually means. Open​AI's long-rumored cheaper variant, GPT-5.6 Sol Ultrafast, keeps getting more concrete, and Deep​Seek spent the week of September 8 to 11 first scheduling its V4 Pro for retirement, then delaying it, then cancelling the retirement outright. Both developments argue for re-running this matchup with fresh numbers rather than trusting the August reviews.

The independent evidence in this piece comes from Artificial Analysis, which lists DeepSeek V4 Pro at a 36 Intelligence Index and GPT-5.6 Sol at 47 — a verified 11-point gap. Deep​Seek's vendor-reported launch benchmarks are labeled as such, because none of them have been reproduced by a third party.

The price gap is the whole argument, and it is bigger than 34x in the cache

On output tokens alone, the ratio is 34x: $20.00 for Sol against $0.60 off-peak for V4 Pro. In a cache-heavy workflow the gap is starker still. DeepSeek V4 Pro's cache-read discount is around 97%, so a long prompt you re-send every request — the system prompt of an agent, the corpus prefix of a RAG loop — costs a hair over two cents per million tokens off-peak. GPT-5.6 Sol's own cache pricing is far more expensive. The blended rate on the Intelligence Index evaluation was $0.69 per million tokens for V4 Pro against roughly $10+ for Sol. For a reader deciding between them, this is the number that settles most workloads.

• Price — GPT-5.6 Sol $4.00/$20.00 per 1M vs DeepSeek V4 Pro $0.66/$1.98 off-peak ($1.32/$3.96 peak)

• Output-price ratio — about 34x at peak list, up to ~50x when V4 Pro's off-peak and cache windows are both in play

• Intelligence Index — Sol 47 (#14/200) vs V4 Pro 36 (#7/113)

• Speed — V4 Pro ~81 tokens/sec vs Sol ~59 tokens/sec

• Context — both 1M tokens

• Modalities — Sol takes text and image input; V4 Pro is text-only

• Weights — V4 Pro MIT-licensed and downloadable; Sol proprietary

The 11-point Intelligence Index gap is real and it is the correct reason to pick Sol when you can afford it. But it is also the only reason, and the price column argues against it more violently than in any other frontier matchup. Sol is not thirty-four times smarter; it is eleven points better on an index where the median open-weight model scores in the high teens.

What September changed

Two things. First, Deep​Seek's own family drama: on September 8, a notice said V4 Pro requests would be routed to V4.1 Flash from September 14 and billed at Flash prices until a V4.1 Pro shipped. On September 10 the cutoff slipped to noon Beijing time on the 14th. On September 11 Deep​Seek reversed the decision entirely, committing to keep serving V4 Pro after the 14th at unchanged billing. Chinese state media and tech outlets confirmed the reversal the same day. The takeaway for this matchup: the affordable half of the comparison is no longer a sunset model, which removes the main argument for "don't bet a production pipeline on the cheap side."

Second, on the other side of the board, Open​AI's GPT-5.6 Sol Ultrafast — the rumored much-cheaper Sol tier — has continued to accumulate evidence over the late summer. If and when it ships, it directly attacks the price argument this article rests on: an Open​AI flagship at a V4-Pro-ish price would make the 34x framing stale within a month. As of September 15, Ultrafast is still unannounced, so the current matchup stands, but this is the piece's open question, not its conclusion.

Who should pay the 34x

Pick GPT-5.6 Sol when the Intelligence Index gap maps to your workload — the eleven points are concentrated in reasoning-heavy, tool-calling, and long-horizon agentic tasks where Sol's evaluation cost of roughly a thousand dollars per index run reflects genuinely harder questions. Pick DeepSeek V4 Pro when you are cost-constrained, token-heavy, or running on your own infrastructure: the MIT weights mean you can serve it yourself for less than the API rate, and the 97% cache discount plus the off-peak window means a high-reuse workload can run at a blended rate an order of magnitude below Sol's.

There is a middle path worth naming: run both. Both DeepSeek V4 Pro and GPT-5.6 Sol are available through OrcaRouter on a single key with provider list prices passed through at zero markup, and the routing DSL makes it easy to send your cheap-and-cheerful traffic to V4 Pro while your hard reasoning tasks go to Sol — the failover covers you if either provider wobbles. That is how this matchup is usually resolved in practice: not by picking one, but by routing between them. (The one caveat: this comparison is about the models themselves. If you want Sol-class intelligence at a fraction of the price, the Ultrafast story is the thing to watch.)

The verdict

GPT-5.6 Sol is the smarter model, GPT-5.6 Sol is eleven points ahead on an independent index, and GPT-5.6 Sol costs thirty-four times as much per output token. The decision, a month after launch, is not a technical one — it is a budget one. If your workload shows the intelligence gap, Sol earns its premium. If it does not, DeepSeek V4 Pro is now the safest cheap option in the frontier class, because after the September 11 reversal it is also the only one with a public commitment to stay on the API.

Send your cheap-and-cheerful traffic to V4 Pro while your hard reasoning tasks go to Sol: GPT-5.6 Sol both on the same key.