LLM Reference

Gemini 3.1 Pro Preview Custom Tools vs GPT-5

Gemini 3.1 Pro Preview Custom Tools (2026) and GPT-5 (2025) are frontier reasoning models from Google DeepMind and OpenAI. Gemini 3.1 Pro Preview Custom Tools ships a 1m-token context window, while GPT-5 ships a 400k-token context window. On pricing, GPT-5 costs $1.25/1M input tokens versus $2/1M 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.

GPT-5 is ~60% cheaper at $1.25/1M; pay for Gemini 3.1 Pro Preview Custom Tools only for long-context analysis.

Decision scorecard

Local evidence first
SignalGemini 3.1 Pro Preview Custom ToolsGPT-5
Best formultimodal apps and long-context analysisreasoning-heavy apps, multimodal apps, and tool-calling agents
Decision fitRAG, Long context, and VisionCoding, RAG, and Agents
Context window1m400k
Cheapest output$12/1M tokens$10/1M tokens
Provider routes1 tracked4 tracked
Shared benchmarks0 shared0 shared

Decision tradeoffs

Choose Gemini 3.1 Pro Preview Custom Tools when...
  • Gemini 3.1 Pro Preview Custom Tools has the larger context window for long prompts, retrieval packs, or transcript analysis.
  • Local decision data tags Gemini 3.1 Pro Preview Custom Tools for RAG, Long context, and Vision.
Choose GPT-5 when...
  • GPT-5 has the lower cheapest tracked output price at $10/1M tokens.
  • GPT-5 has broader tracked provider coverage for fallback and route flexibility.
  • GPT-5 uniquely exposes Reasoning, JSON / Tool use, and Code execution in local model data.
  • Local decision data tags GPT-5 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 GPT-5

Gemini 3.1 Pro Preview Custom Tools

$4,600

Cheapest tracked route/tier: OpenRouter

GPT-5

$3,500

Cheapest tracked route/tier: Replicate API

Estimated monthly gap: $1,100. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.

Switch friction

Gemini 3.1 Pro Preview Custom Tools -> GPT-5
  • Provider overlap exists on OpenRouter; start route-level A/B tests there.
  • GPT-5 is $2/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
  • GPT-5 adds Reasoning, JSON / Tool use, and Code execution in local capability data.
GPT-5 -> Gemini 3.1 Pro Preview Custom Tools
  • Provider overlap exists on OpenRouter; start route-level A/B tests there.
  • Gemini 3.1 Pro Preview Custom Tools is $2/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
  • Check replacement coverage for Reasoning, JSON / Tool use, and Code execution before moving production traffic.

Specs

Specification
Released2026-01-012025-08-07
Context window1m400k
Parameters——
ArchitectureDecoder OnlyDecoder Only
LicenseProprietaryProprietary
OpennessProprietaryProprietary
WeightsNot releasedNot released
CodeUnknownUnknown
Commercial useCommercial use: conditionalCommercial use: conditional
Knowledge cutoff2025-012024-09

Pricing and availability

Pricing attributeGemini 3.1 Pro Preview Custom ToolsGPT-5
Input price$2/1M tokens$1.25/1M tokens
Output price$12/1M tokens$10/1M tokens
Providers
OpenRouter
Replicate APIOpenRouterOpenAI APIVercel AI Gateway

Capabilities

CapabilityGemini 3.1 Pro Preview Custom ToolsGPT-5
VisionYesYes
MultimodalYesYes
ReasoningNoYes
JSON / Tool useNoYes
Structured outputsYesYes
Code executionNoYes
IDE integrationNoNo
Computer useNoNo
Parallel agentsNoNo

Benchmarks

No shared benchmark scores are currently available for this pair.

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