GPT-5.6 Sol vs DeepSeek V4 Flash

What I tested — same prompt, two models

I run the same fixed prompt set through every new model the day it drops — same string, one shot, single HTML file out — and I score the result 0–10 on whether it ran, how close it hit the brief, and how good it looked. Below is what came out when I gave the exact same prompts to GPT-5.6 Sol and DeepSeek V4 Flash, side by side, on 50 shared tasks inside the Agent Operating System.

Both models were given identical prompts inside the Agent Operating System — no help, no iteration, no "best of N" tricks. I run each prompt once, save the HTML file the model produces, and score it 0–10 on whether it ran, how close it hit the brief, and how good it looked. The scoring is mine. The verdicts below are pulled from my source comparison guides at agentos.guide where I publish every score and the reasoning behind it.

GPT-5.6 Sol · Benched on GoldieBench as the flagship Sol at medium reasoning, one-shot, then headless-playtested. In the Agent OS it's the top tier of a routed stack — Sol on the hard calls, Terra for the bulk, Luna for the everyday 90%.

DeepSeek V4 Flash · Wired into the Agent OS three ways: a `deepseek` Hermes profile, the DeepSeek Coder tab (official API, V4 Flash 0731 / V4 Pro picker, live preview), and the OpenCode model dropdown. Benched on all 50 GoldieBench tasks via api.deepseek.com — the endpoint the 0731 beta shipped on — with the skill-infused threejs-game-director prompt on game tasks and a model-driven fix round on any build that failed the render check.

Strengths & weaknesses I logged

Pricing & context — the spec sheet

The verdict — which should you pick?

Not enough scored shared tasks yet for a head-to-head average. The live demos for both are on the matrix above — play them and form your own opinion.

If you only run one of these inside your stack, the head-to-head average above is the call. If you can run both, my honest play is to wire GPT-5.6 Sol and DeepSeek V4 Flash both into the Agent Operating System and dispatch each from the kanban by task type — the hardest reasoning and code where being right beats being cheap → GPT-5.6 Sol, long agent loops and codex-style write-run-fix work, which is what the 0731 upgrade targets → DeepSeek V4 Flash. That's the same setup I run for the 4,000+ founders inside the AI Profit Boardroom.

FAQ — GPT-5.6 Sol vs DeepSeek V4 Flash

Which is better, GPT-5.6 Sol or DeepSeek V4 Flash?

On Goldie Bench, GPT-5.6 Sol averages no scored verdicts yet across the shared tasks, with 3 gold, 8 silver, 12 bronze overall. DeepSeek V4 Flash averages no scored verdicts yet, with 0 gold, 0 silver, 0 bronze. Not enough scored shared tasks yet to call a winner.

How much does GPT-5.6 Sol cost vs DeepSeek V4 Flash?

GPT-5.6 Sol: GPT-5.6 shipped as three models — Luna ($1/$6 per M), Terra ($2.50/$15) and Sol ($5/$30) — each with a same-price pro variant that ships a higher default reasoning effort. All share a ~1.05M-token context window and are rated High capability. Benched here on the flagship, Sol, at medium reasoning effort via OpenRouter. DeepSeek V4 Flash: Benched on the DeepSeek-V4-Flash-0731 public beta, launched 2026-07-31 on DeepSeek's official API. DeepSeek describe it as a major upgrade to agent capabilities whose benchmark scores now surpass their previous V4-Pro-Preview, using the exact same model architecture and size as the preview — the gain is post-training, not scale. Natively supports the Responses API format and is adapted for Codex-style coding loops. Benched against api.deepseek.com directly because third-party routes list "v4-flash" undated and may still serve the older preview build.

What's the context window for GPT-5.6 Sol vs DeepSeek V4 Flash?

GPT-5.6 Sol has a 1,050,000 tokens context window. DeepSeek V4 Flash has a 1,000,000-token context window context window.

When should I pick GPT-5.6 Sol over DeepSeek V4 Flash?

Pick GPT-5.6 Sol for: The hardest reasoning and code where being right beats being cheap; One-shot game/sim prototypes you want shippable on the first prompt; The flagship slot in a routed Agent OS — Sol for the hard 10%, Luna/Terra for the rest. The trade-off is the weaknesses we logged on the bench: Priciest tier on the bench at $30/M output — only worth routing the hardest 10% of work to Sol; Reasoning can eat the token budget on big open-world briefs (one 0-byte failure until the budget was raised, then it built clean).

When should I pick DeepSeek V4 Flash over GPT-5.6 Sol?

Pick DeepSeek V4 Flash for: Long agent loops and Codex-style write-run-fix work, which is what the 0731 upgrade targets; Whole-repo or whole-document tasks that need the 1M context on a cheap tier; Volume build work where you would rather wait a few minutes than pay a flagship. The trade-off is the weaknesses we logged on the bench: Unranked — the 50 builds are on the bench but not yet scored by the Opus vision judge; Reasons at length before writing (a full 3D game build ran ~4-8 minutes), so it is not a fast-draft model; 8 of 50 first-pass builds rendered black or near-black before the fix round.

How does Goldie Bench score GPT-5.6 Sol vs DeepSeek V4 Flash?

Every demo on this page was built by Julian Goldie inside the Agent Operating System — same fixed prompt for both models, one shot, single HTML file out. Each result gets a 0–10 score on whether it ran, how close it hit the brief, and how good it looked. The highest score on each task gets gold; second gets silver; third gets bronze. See methodology for full provenance.

Related comparisons

Other head-to-heads using the same scoring system:

Full model pages: GPT-5.6 Sol · DeepSeek V4 Flash · back to the leaderboard