o3 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
o3 specs · Phi-3.5 Medium specs- Priceo3
o3 publishes pricing ($8.00 / 1M output tokens) while Phi-3.5 Medium does not.
- Context windowo3
o3 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.
- Modalitieso3
o3 supports 2 modalities (text, vision) vs 1 for Phi-3.5 Medium.
- OpennessPhi-3.5 Medium
Phi-3.5 Medium ships open weights (MIT); o3 is API-only.
On balance o3 edges ahead, winning 3 of 5 categories against Phi-3.5 Medium's 1. o3 publishes pricing ($8.00 / 1M output tokens) while Phi-3.5 Medium does not. o3 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, o3 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); o3 is API-only.
o3 is the newer of the two, released 8 months after Phi-3.5 Medium, which usually means a more recent knowledge cutoff and updated safety post-training. o3 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
| Spec | o3 | Phi-3.5 Medium |
|---|---|---|
| Provider | OpenAI | Microsoft |
| Released | Apr 2025 | Aug 2024 |
| Modalities | text, vision | text |
| Context window | 200K tokens | 128K tokens |
| Max output | , | , |
| Input · 1M | $2.00 / 1M tokens | Pricing not published |
| Output · 1M | $8.00 / 1M tokens | Pricing not published |
| Knowledge cutoff | 2024-06 | , |
| Open weights | No | Yes (MIT) |
| API available | Yes | Yes |
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$18.00 vs ,
- Heavy usage, 1M in / 500k out per day$180 vs ,
- RAG workload, 5M in / 200k out per day$348 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).
Estimated spend for the listed models at your usage. Numbers are derived from each model's published per-million-token rates.
- o3$0.600
- 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.
- MMLU,78.9
- HumanEval95.0
- GPQA87.7
o3 fits when…
- Industry-leading reasoning depth at launch
- Strong on math, science, and abstract puzzles
- Tool-use during reasoning loops
- Long-context tasks, handles 200K tokens vs 128K for Phi-3.5 Medium.
- Multimodal needs covering vision.
Phi-3.5 Medium fits when…
- MIT license
- 128k context
- Strong reasoning at 14B
- Self-hosting and on-prem requirements, open weights (MIT).
Consider GPT-5.5
OpenAI's mid-cycle GPT-5 refresh, improved reasoning, tool use, and multimodal grounding over the 2025 launch.
Frequently asked
Is o3 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?
o3 accepts 200K tokens vs 128K for Phi-3.5 Medium.Is o3 or Phi-3.5 Medium better for coding?
Both o3 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). o3 is API-only.When were o3 and Phi-3.5 Medium released?
o3 was released by OpenAI on 2025-04-16. Phi-3.5 Medium was released by Microsoft on 2024-08-20.
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