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LLM Toolkit

Model comparison

GPT-5 vs Gemini 3.5 Flash

Verified pricing, context windows and real-workload costs for both models — computed from official provider rates as of 2026-08-25.

Cheaper input

GPT-5

$1.25 /1M in

Cheaper output

Gemini 3.5 Flash

$9.00 /1M out

Bigger context

Gemini 3.5 Flash

1M tokens

Head to head

Spec GPT-5 Gemini 3.5 Flash
Input / 1M tokens $1.25 $1.50
Cached input / 1M $0.13 —
Output / 1M tokens $10.00 $9.00
Context window 400K 1M
Provider OpenAI Google
Price verified 2026-08-25 2026-08-25

Monthly cost at three real workloads

Workload GPT-5 Gemini 3.5 Flash Winner
Side-project chatbot 30K req · 2,000 in / 500 out · 40% cached $198.00/mo $225.00/mo GPT-5
Coding agent 500K req · 12,000 in / 1,500 out · 70% cached $10,275/mo $15,750/mo GPT-5
Bulk extraction 2,000K req · 800 in / 120 out · 20% cached $4,040/mo $4,560/mo GPT-5

Computed from list prices verified 2026-08-25. Cache savings blend normal and cached input rates by the hit rate; models without published cached rates use the base input price. Adjust every parameter yourself on the API Cost Calculator.

Pick GPT-5 if…

  • Input cost dominates your bill — it charges $1.25 per 1M input vs $1.50.
  • Your documents fit its 400K window comfortably.
  • You run repeat-context workloads — cached input at $0.13 per 1M is the better deal.

Pick Gemini 3.5 Flash if…

  • You generate long outputs — $9.00 per 1M output vs $10.00 adds up fast.
  • You need 1M tokens of context for large codebases or document sets.
  • You want cheaper total spend at your exact volumes — verify with the calculator above.

Frequently asked questions

Is GPT-5 cheaper than Gemini 3.5 Flash?

GPT-5 is cheaper on input at $1.25 per 1M tokens vs $1.50 — input pricing is 1.2× less expensive. On output, Gemini 3.5 Flash wins at $9.00 vs $10.00. At a balanced workload (100K requests, 2K in / 500 out), GPT-5 runs $750.00/mo vs $750.00/mo — a negligible difference.

GPT-5 vs Gemini 3.5 Flash: which has the bigger context window?

Gemini 3.5 Flash, with 1M tokens vs 400K — 2.5× more room. Filling Gemini 3.5 Flash's window once costs $1.50 at list price, vs $0.500 for the smaller window.

Should I switch from GPT-5 to Gemini 3.5 Flash?

Switch if your bottleneck matches Gemini 3.5 Flash's strengths: the larger 1M context and cheaper output tokens ($9.00 vs $10.00). Stay on GPT-5 if input cost dominates your bill — GPT-5 charges $1.25 per 1M in. Test both with your real token counts before committing.

Keep comparing

Or measure your real usage with the AI Token Counter and browse all rates on the Pricing Comparison.