o4-mini vs Phi 3.5 Mini Instruct
o4-mini (2025) and Phi 3.5 Mini Instruct (2024) are frontier reasoning models from OpenAI and Microsoft Research. o4-mini ships a 200k-token context window, while Phi 3.5 Mini Instruct ships a 128k-token context window. On pricing, Phi 3.5 Mini Instruct costs $0.90/1M input tokens versus $1/1M 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.
o4-mini is safer overall; choose Phi 3.5 Mini Instruct when provider fit matters.
Decision scorecard
Local evidence first| Signal | o4-mini | Phi 3.5 Mini Instruct |
|---|---|---|
| Best for | reasoning-heavy apps, multimodal apps, and tool-calling agents | provider-routed production |
| Decision fit | Coding, RAG, and Agents | Long context |
| Context window | 200k | 128k |
| Cheapest output | $4/1M tokens | $0.90/1M tokens |
| Provider routes | 4 tracked | 2 tracked |
| Shared benchmarks | 0 rows | 0 rows |
Decision tradeoffs
- o4-mini has the larger context window for long prompts, retrieval packs, or transcript analysis.
- o4-mini has broader tracked provider coverage for fallback and procurement flexibility.
- o4-mini uniquely exposes Vision, Multimodal, and Reasoning in local model data.
- Local decision data tags o4-mini for Coding, RAG, and Agents.
- Phi 3.5 Mini Instruct has the lower cheapest tracked output price at $0.90/1M tokens.
- Local decision data tags Phi 3.5 Mini Instruct for Long context.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output route or tier on this page.
o4-mini
$1,800
Cheapest tracked route/tier: Replicate API
Phi 3.5 Mini Instruct
$945
Cheapest tracked route/tier: Fireworks AI
Estimated monthly gap: $855. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.
Switch friction
- No overlapping tracked provider route is sourced for o4-mini and Phi 3.5 Mini Instruct; plan for SDK, billing, or endpoint changes.
- Phi 3.5 Mini Instruct is $3.10/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- Check replacement coverage for Vision, Multimodal, and Reasoning before moving production traffic.
- No overlapping tracked provider route is sourced for Phi 3.5 Mini Instruct and o4-mini; plan for SDK, billing, or endpoint changes.
- o4-mini is $3.10/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- o4-mini adds Vision, Multimodal, and Reasoning in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2025-04-16 | 2024-08-20 |
| Context window | 200k | 128k |
| Parameters | — | 3.8B |
| Architecture | decoder only | decoder only |
| License | Proprietary | MIT(OSI) |
| Openness | Proprietary | Open source |
| Commercial use | Commercial use with conditions | Commercial use allowed |
| Knowledge cutoff | 2025-08 | 2023-10 |
Pricing and availability
| Pricing attribute | o4-mini | Phi 3.5 Mini Instruct |
|---|---|---|
| Input price | $1/1M tokens | $0.90/1M tokens |
| Output price | $4/1M tokens | $0.90/1M tokens |
| Providers |
Capabilities
| Capability | o4-mini | Phi 3.5 Mini Instruct |
|---|---|---|
| Vision | Yes | No |
| Multimodal | Yes | No |
| Reasoning | Yes | No |
| Function calling | Yes | No |
| Tool use | Yes | No |
| Structured outputs | Yes | No |
| Code execution | Yes | No |
| IDE integration | No | No |
| Computer use | No | No |
| Parallel agents | No | No |
Benchmarks
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on vision: o4-mini, multimodal input: o4-mini, reasoning mode: o4-mini, function calling: o4-mini, tool use: o4-mini, structured outputs: o4-mini, and code execution: o4-mini. Both models share the core language-model surface, so the practical split is not just feature count. Use those differences to decide whether the page is about raw model quality, agentic coding support, multimodal ingestion, or predictable structured API behavior.
For cost, o4-mini lists $1/1M input and $4/1M output tokens on the cheapest tracked provider, while Phi 3.5 Mini Instruct lists $0.90/1M input and $0.90/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts Phi 3.5 Mini Instruct lower by about $1.00 per million blended tokens. Availability is 4 providers versus 2, so concentration risk also matters.
Choose o4-mini when coding workflow support, larger context windows, and broader provider choice are central to the workload. Choose Phi 3.5 Mini Instruct when provider fit and lower input-token cost are more important. For production, rerun your own prompts through the exact provider, region, and tool stack you plan to ship. This keeps the decision grounded in measurable tradeoffs instead of brand-level assumptions.
FAQ
Which has a larger context window, o4-mini or Phi 3.5 Mini Instruct?
o4-mini supports 200k tokens, while Phi 3.5 Mini Instruct supports 128k tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible.
Which is cheaper, o4-mini or Phi 3.5 Mini Instruct?
Phi 3.5 Mini Instruct is cheaper on tracked token pricing. o4-mini costs $1/1M input and $4/1M output tokens. Phi 3.5 Mini Instruct costs $0.90/1M input and $0.90/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is o4-mini or Phi 3.5 Mini Instruct open source?
o4-mini is listed under Proprietary. Phi 3.5 Mini Instruct is listed under MIT. License labels affect whether you can self-host, redistribute weights, or rely only on hosted APIs, so confirm the upstream license before deployment.
Which is better for vision, o4-mini or Phi 3.5 Mini Instruct?
o4-mini has the clearer documented vision signal in this comparison. If vision is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.
Which is better for multimodal input, o4-mini or Phi 3.5 Mini Instruct?
o4-mini has the clearer documented multimodal input signal in this comparison. If multimodal input is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Where can I run o4-mini and Phi 3.5 Mini Instruct?
o4-mini is available on OpenAI API, OpenRouter, Replicate API, and Vercel AI Gateway. Phi 3.5 Mini Instruct is available on Fireworks AI and NVIDIA NIM. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
Continue comparing
Last reviewed: 2026-05-22. Data sourced from public model cards and provider documentation.