gemini 3.1 pro preview is Google's frontier-tier reasoning model in the 3.1 generation, the one to reach for when a task needs multiple steps of thinking, not just fast pattern matching. It's built for coding, complex analysis, and agentic problem solving where getting the answer right matters more than shaving a few cents off the bill. Developers building coding assistants, research agents, or anything that chains several reasoning steps together are the target audience.
Context, output, and pricing
The model carries a 1,048,576 token context window with up to 65,536 tokens of output per call — enough room to hold a full codebase excerpt, a long research thread, or a multi-document brief in one request. Input tokens cost $2.00 per million, output tokens $12.00 per million, and cached input is $0.20 per million. That 6x output-to-input price ratio is worth planning around: verbose responses cost real money here, so prompts that ask for concise, structured output pay off more than they would on a cheaper tier.
What it's built to do well
- Multi-step coding tasks — debugging, refactoring, or reasoning through a change across several files
- Complex analysis where the model needs to hold a large document or codebase in context
- Agentic workflows that combine reasoning with function calling
- Vision-plus-reasoning tasks: reading a screenshot, diagram, or PDF and reasoning about it, not just describing it
How it compares within the 3.1 family
Gemini 3.1 Flash Lite Preview costs $0.25 per million input and $1.50 per million output — an 8x discount on both sides — and posts a capability score of 88.6 against Pro Preview's 88.5. On paper those scores are nearly identical, which is a real signal: for tasks that don't need Pro's depth, Flash Lite is worth testing first, and reserving Pro for the harder end of the workload where multi-step reasoning actually shows up is the more defensible default than routing everything to the most expensive tier.
The honest limitation
As a preview release, pricing, output limits, and availability aren't locked in, and Google can change them before general availability ships. There's no benchmark suite attached to this listing, so treat capability comparisons as a rough signal, not a ranking — run your own eval against your own task before committing a production workload to it.