Gemini 2.5 Flash vs Gemini 3.5 Flash

Gemini 2.5 Flash (2025) and Gemini 3.5 Flash (2026) are frontier reasoning models from Google DeepMind. Gemini 2.5 Flash ships a 1m-token context window, while Gemini 3.5 Flash ships a 1.05m-token context window. On Google-Proof Q&A, Gemini 3.5 Flash leads by 9.4 pts. On pricing, Gemini 2.5 Flash costs $0.30/1M input tokens versus $1.50/1M for the alternative. This comparison covers specs, pricing, API access, capabilities, benchmarks, input and output token costs, and production fit for coding and agent workloads.

Gemini 2.5 Flash is ~400% cheaper at $0.30/1M; pay for Gemini 3.5 Flash only for coding workflow support.

Decision scorecard

Local evidence first
SignalGemini 2.5 FlashGemini 3.5 Flash
Best formultimodal apps, tool-calling agents, and long-context analysisreasoning-heavy apps, multimodal apps, and tool-calling agents
Decision fitCoding, RAG, and AgentsCoding, RAG, and Agents
Context window1m1.05m
Cheapest output$2.50/1M tokens$9/1M tokens
Provider routes6 tracked4 tracked
Shared benchmarks3 sharedGoogle-Proof Q&A leader

Decision tradeoffs

Choose Gemini 2.5 Flash when...
  • Gemini 2.5 Flash has the lower cheapest tracked output price at $2.50/1M tokens.
  • Gemini 2.5 Flash has broader tracked provider coverage for fallback and route flexibility.
  • Local decision data tags Gemini 2.5 Flash for Coding, RAG, and Agents.
Choose Gemini 3.5 Flash when...
  • Gemini 3.5 Flash holds a shared-benchmark lead on Google-Proof Q&A, ahead by 9.4 points.
  • Gemini 3.5 Flash has the larger context window for long prompts, retrieval packs, or transcript analysis.
  • Gemini 3.5 Flash uniquely exposes Reasoning in local model data.
  • Local decision data tags Gemini 3.5 Flash for Coding, RAG, and Agents.

Monthly cost at traffic

Estimate token spend from the cheapest tracked input and output route or tier on this page.

Lower estimate Gemini 2.5 Flash

Gemini 2.5 Flash

$865

Cheapest tracked route/tier: Google AI Studio

Gemini 3.5 Flash

$3,450

Cheapest tracked route/tier: Google AI Studio

Estimated monthly gap: $2,585. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.

Switch friction

Gemini 2.5 Flash -> Gemini 3.5 Flash
  • Provider overlap exists on Google AI Studio, GCP Vertex AI, and Vercel AI Gateway; start route-level A/B tests there.
  • Gemini 3.5 Flash is $6.50/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
  • Gemini 3.5 Flash adds Reasoning in local capability data.
Gemini 3.5 Flash -> Gemini 2.5 Flash
  • Provider overlap exists on Google AI Studio, GCP Vertex AI, and OpenRouter; start route-level A/B tests there.
  • Gemini 2.5 Flash is $6.50/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
  • Check replacement coverage for Reasoning before moving production traffic.

Specs

Specification
Released2025-06-172026-05-19
Context window1m1.05m
Parameters——
ArchitectureDecoder OnlyDecoder Only
LicenseProprietaryProprietary
OpennessProprietaryProprietary
WeightsNot releasedNot released
CodeUnknownUnknown
Commercial useCommercial use: conditionalCommercial use: conditional
Knowledge cutoff2025-012025-01

Pricing and availability

Pricing attributeGemini 2.5 FlashGemini 3.5 Flash
Input price$0.30/1M tokens$1.50/1M tokens
Output price$2.50/1M tokens$9/1M tokens
Providers
Google AI StudioGCP Vertex AIReplicate APIOpenRouterVercel AI GatewayInceptron
Google AI StudioGCP Vertex AIVercel AI GatewayOpenRouter

Capabilities

CapabilityGemini 2.5 FlashGemini 3.5 Flash
VisionYesYes
MultimodalYesYes
ReasoningNoYes
JSON / Tool useYesYes
Structured outputsYesYes
Code executionYesYes
IDE integrationNoNo
Computer useNoNo
Parallel agentsNoNo

Benchmarks

BenchmarkGemini 2.5 FlashGemini 3.5 Flash
Google-Proof Q&A82.892.2
Massive Multi-discipline Multimodal Understanding79.783.6
HumanEval90.192.0

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Last reviewed: 2026-06-29. Data sourced from public model cards and provider documentation.