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Gemini 2.5 Flash Preview 09-2025

Gemini 2.5 Flash Preview 09-2025 is Google's September 2025 preview of the next Gemini 2.5 Flash, scoring 54% on SWE-Bench Verified (up from 48.9%), improving agentic tool use, and producing 24% fewer output tokens with thinking enabled.

File InputImplicit CachingReasoningTool UseVision (Image)Web Search
index.ts
import { streamText } from 'ai'


const result = streamText({
  model: 'google/gemini-2.5-flash-preview-09-2025',
  prompt: 'Why is the sky blue?'
})
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Frequently Asked Questions

  • What is the SWE-Bench Verified improvement in Gemini 2.5 Flash Preview 09-2025?

    The score moved from 48.9% on the stable model to 54% on this preview. SWE-Bench Verified tests a model's ability to resolve real software engineering tasks from production repositories.

  • How much do thinking tokens cost with Gemini 2.5 Flash Preview 09-2025?

    Google reported a 24% reduction in output tokens compared to the stable model when thinking is active. The per-token rate stays the same, but you consume fewer tokens per reasoning task.

  • Is this preview a replacement for the stable Gemini 2.5 Flash?

    No. Google released it for developer feedback. It may reach stable later or be superseded. Pin to the explicit model string and monitor deprecation notices.

  • Does Gemini 2.5 Flash Preview 09-2025 support thinking budgets like the stable 2.5 Flash?

    Yes. The hybrid reasoning design carries forward. You can disable thinking entirely or set a budget that controls how much deliberation the model applies per request.

  • How do I authenticate requests to Gemini 2.5 Flash Preview 09-2025 through AI Gateway?

    Use a Vercel API key or OIDC token with AI Gateway. Use the identifier google/gemini-2.5-flash-preview-09-2025 in your API calls. AI Gateway manages routing, retries, and failover across google, vertex.

  • Can I use the -latest alias instead of the dated preview string?

    Google offers aliases like gemini-flash-latest that auto-update to the newest preview. These rotate with two-week deprecation notices. Use the explicit gemini-2.5-flash-preview-09-2025 string for reproducible behavior.

  • How does Gemini 2.5 Flash Preview 09-2025 compare to Gemini 2.5 Pro?

    2.5 Flash (including this preview) sits on the cost-performance frontier. It delivers strong reasoning at lower cost than 2.5 Pro. For the hardest problems where benchmark scores justify the premium, 2.5 Pro remains the Pro tier in the 2.5 family.