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o4 vs Phi-3.5 Medium

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

Updated

o4 specs · Phi-3.5 Medium specs
Verdict by category
  • PriceTie

    Neither model publishes per-token API pricing.

  • Context windowo4

    o4 accepts 200K tokens vs 128K, 1.6× 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.

  • Modalitieso4

    o4 supports 2 modalities (text, vision) vs 1 for Phi-3.5 Medium.

  • OpennessPhi-3.5 Medium

    Phi-3.5 Medium ships open weights (MIT); o4 is API-only.

On balance o4 edges ahead, winning 2 of 5 categories against Phi-3.5 Medium's 1. Neither model publishes per-token API pricing. o4 accepts 200K tokens vs 128K, 1.6× 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, o4 handles text, vision while Phi-3.5 Medium handles text, which can be the deciding factor before you even look at benchmarks. Phi-3.5 Medium ships open weights (MIT); o4 is API-only.

o4 is the newer of the two, released 16 months after Phi-3.5 Medium, which usually means a more recent knowledge cutoff and updated safety post-training. o4 is usually picked for reasoning and math workloads, while Phi-3.5 Medium sees more deployments in on device and edge deployment. If pricing matters more than every last benchmark point, run the numbers in the calculator below before committing.

Side-by-side specs

Speco4Phi-3.5 Medium
ProviderOpenAIMicrosoft
ReleasedDec 2025Aug 2024
Modalitiestext, visiontext
Context window200K tokens128K tokens
Max output,,
Input · 1MPricing not publishedPricing not published
Output · 1MPricing not publishedPricing not published
Knowledge cutoff,,
Open weightsNoYes (MIT)
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, vs ,
  • Heavy usage, 1M in / 500k out per day, vs ,
  • RAG workload, 5M in / 200k out per day, 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.

  • o4Pricing unavailable
  • Phi-3.5 MediumPricing unavailable

Benchmarks compared

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

o4Phi-3.5 Medium
  • MMLU,78.9
Pick o4 if

o4 fits when…

  • Exceptional performance on hard math and reasoning benchmarks
  • Good at multi-step planning and verification
  • Strong scientific reasoning
  • Long-context tasks, handles 200K tokens vs 128K for Phi-3.5 Medium.
  • Multimodal needs covering vision.
Pick Phi-3.5 Medium if

Phi-3.5 Medium fits when…

  • MIT license
  • 128k context
  • Strong reasoning at 14B
  • Self-hosting and on-prem requirements, open weights (MIT).
Don't want either?

Consider GPT-5.5

OpenAI's mid-cycle GPT-5 refresh, improved reasoning, tool use, and multimodal grounding over the 2025 launch.

See GPT-5.5 specso4 vs GPT-5.5Phi-3.5 Medium vs GPT-5.5

Frequently asked

  • Is o4 or Phi-3.5 Medium 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?
    o4 accepts 200K tokens vs 128K for Phi-3.5 Medium.
  • Is o4 or Phi-3.5 Medium better for coding?
    Both o4 and Phi-3.5 Medium 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?
    Phi-3.5 Medium ships open weights (MIT). o4 is API-only.
  • When were o4 and Phi-3.5 Medium released?
    o4 was released by OpenAI on 2025-12-15. Phi-3.5 Medium was released by Microsoft on 2024-08-20.
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