LLM·Dex
Newsletter

Gemini 2.5 Flash vs o4

A complete head-to-head: pricing, context window, benchmarks, modality coverage, and openness, with a programmatic verdict synthesized from the underlying data.

Updated

Gemini 2.5 Flash specs · o4 specs
Verdict by category
  • PriceGemini 2.5 Flash

    Gemini 2.5 Flash publishes pricing ($0.30 / 1M output tokens) while o4 does not.

  • Context windowGemini 2.5 Flash

    Gemini 2.5 Flash accepts 1.0M tokens vs 200K, 5.2× the room for long documents and codebases.

  • BenchmarksTie

    No directly comparable public benchmarks are available for both models, check the spec sheets for individual scores.

  • ModalitiesGemini 2.5 Flash

    Gemini 2.5 Flash supports 3 modalities (text, vision, audio) vs 2 for o4.

  • OpennessTie

    Both are closed-weight, API-only.

On balance Gemini 2.5 Flash edges ahead, winning 3 of 5 categories against o4's 0. Gemini 2.5 Flash publishes pricing ($0.30 / 1M output tokens) while o4 does not. Gemini 2.5 Flash accepts 1.0M tokens vs 200K, 5.2× the room for long documents and codebases.

No directly comparable public benchmarks are available for both models, check the spec sheets for individual scores. They differ in modality coverage, Gemini 2.5 Flash handles text, vision, audio while o4 handles text, vision, which can be the deciding factor before you even look at benchmarks. Both are closed-weight, API-only.

o4 is the newer of the two, released 8 months after Gemini 2.5 Flash, which usually means a more recent knowledge cutoff and updated safety post-training. Gemini 2.5 Flash is usually picked for rag and long context workloads, while o4 sees more deployments in reasoning and math. If pricing matters more than every last benchmark point, run the numbers in the calculator below before committing.

Side-by-side specs

SpecGemini 2.5 Flasho4
ProviderGoogleOpenAI
ReleasedApr 2025Dec 2025
Modalitiestext, vision, audiotext, vision
Context window1.0M tokens200K tokens
Max output,,
Input · 1M$0.075 / 1M tokensPricing not published
Output · 1M$0.30 / 1M tokensPricing not published
Knowledge cutoff2025-01,
Open weightsNoNo
API availableYesYes

Pricing at scale

What you'd actually pay at typical workloads. Numbers come from each model's published per-million-token rates.

  • Light usage, 100k in / 50k out per day$0.675 vs ,
  • Heavy usage, 1M in / 500k out per day$6.75 vs ,
  • RAG workload, 5M in / 200k out per day$13.05 vs ,

Light usage, 100k in / 50k out per day: pricing not directly comparable (one or both models are missing public per-token rates). Heavy usage, 1M in / 500k out per day: pricing not directly comparable (one or both models are missing public per-token rates). RAG workload, 5M in / 200k out per day: pricing not directly comparable (one or both models are missing public per-token rates).

Price calculator

Estimated spend for the listed models at your usage. Numbers are derived from each model's published per-million-token rates.

  • Gemini 2.5 Flash$0.022
  • o4Pricing unavailable

Benchmarks compared

Only sourced numbers. Where a benchmark is missing for one model we show the available value rather than fabricating the other.

Benchmark scores not yet available. We only publish numbers we can source from official model cards or independent leaderboards, see methodology.
Pick Gemini 2.5 Flash if

Gemini 2.5 Flash fits when…

  • Cheap and fast
  • Long context
  • Solid vision
  • Long-context tasks, handles 1.0M tokens vs 200K for o4.
  • Multimodal needs covering audio.
Pick o4 if

o4 fits when…

  • Exceptional performance on hard math and reasoning benchmarks
  • Good at multi-step planning and verification
  • Strong scientific reasoning
Don't want either?

Consider Gemini 3 Pro

Google's late-2025 flagship, set new benchmarks on long-context, vision, and reasoning at competitive pricing.

See Gemini 3 Pro specsGemini 2.5 Flash vs Gemini 3 Proo4 vs Gemini 3 Pro

Frequently asked

  • Is Gemini 2.5 Flash or o4 cheaper?
    Per-token pricing isn't published for at least one of these models, check each model's spec page for current rates.
  • Which has the larger context window?
    Gemini 2.5 Flash accepts 1.0M tokens vs 200K for o4.
  • Is Gemini 2.5 Flash or o4 better for coding?
    Both Gemini 2.5 Flash and o4 are competitive on coding benchmarks. See each model's individual spec page for HumanEval and SWE-bench scores where published. For an opinionated pick, consult our Best LLM for Coding ranking.
  • Are either of these models open source?
    Neither model ships open weights, both are accessible only via their respective providers' APIs.
  • When were Gemini 2.5 Flash and o4 released?
    Gemini 2.5 Flash was released by Google on 2025-04-09. o4 was released by OpenAI on 2025-12-15.
Friday digest

The week's AI launches, in your inbox.

One short email every Friday, new models, leaks, and quietly-shipped APIs you missed.