Flash or Pro? A rule that saves time and money.
Two models, one easy heuristic. Pick wrong and you either overpay or under-think the problem. Here is how to choose in five seconds.
Default to Flash. Switch to Pro only when the task has real multi-step reasoning and the cost of a wrong answer is high. Most work is a Flash job; Pro is for the hard 10%.
01V4 Flash — the workhorse
Fast, extremely cheap, and strong enough for the large majority of tasks: drafting, summarizing, everyday coding, classification, and high-volume jobs where price per call matters. When in doubt, start here.
02V4 Pro — for the hard 10%
Slower and pricier, but it reasons more deeply: tricky math and logic, gnarly debugging, multi-constraint planning, and analysis where being right matters more than being fast. If Flash gives a shaky answer on a hard problem, escalate to Pro.
Flash just got a serious upgrade. DeepSeek released V4-Flash-0731, the official version of V4 Flash that supersedes the April preview. Same architecture, re-trained: on DeepSeek’s own published agent and coding benchmarks the new Flash now scores above the V4 Pro preview — Terminal Bench 2.1 jumps to 82.7 (the Pro preview scores 72.1), and it adds a third reasoning-effort level (low / high / max). The open weights are on Hugging Face under an MIT license. The 5-second rule still holds, but the “hard 10%” just got smaller: for agentic and coding work especially, give Flash the first shot before paying up for Pro.
03The shared superpower: ~1M tokens
Both models share a very large context window — roughly a million tokens — so the choice is about depth of reasoning, not how much they can read. Either one can ingest an entire report or codebase; Pro just thinks harder about it.