GPT OSS 20B vs Phi-3.5-mini-instruct
GPT OSS 20B significantly outperforms across most benchmarks. GPT OSS 20B is 1.1x cheaper per token.
OpenAI · Microsoft · Updated for 2026
Which is better?
GPT OSS 20B outperforms in 2 benchmarks (GPQA, MMLU), while Phi-3.5-mini-instruct is better at 0 benchmarks. GPT OSS 20B significantly outperforms across most benchmarks.
On price, GPT OSS 20B is roughly 1.1x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.
GPT OSS 20B also accepts a larger context window (131,072 input tokens), making it the stronger choice for long documents and large codebases.
Based on current benchmark, pricing, and model metadata for 2026.
Choose GPT OSS 20B
- you want the strongest raw capability — it leads on 2 of 2 shared benchmarks
- cost matters — it's about 1.1x cheaper per token
- you process long inputs — it offers a 131,072 token context window
- you want the most recent training data — it shipped Aug 2025
Choose Phi-3.5-mini-instruct
- you want predictable pricing at $0.10/M input and $0.10/M output
At a glance
The differences that matter most.
Performance Benchmarks
Comparative analysis across standard metrics
GPT OSS 20B outperforms in 2 benchmarks (GPQA, MMLU), while Phi-3.5-mini-instruct is better at 0 benchmarks.
GPT OSS 20B significantly outperforms across most benchmarks.
Arena Performance
Playground indexes and blind preference scores
Pricing Analysis
Price comparison per million tokens
For input processing, GPT OSS 20B ($0.05/1M tokens) is 2.0x cheaper than Phi-3.5-mini-instruct ($0.10/1M tokens).
For output processing, GPT OSS 20B ($0.20/1M tokens) is 2.0x more expensive than Phi-3.5-mini-instruct ($0.10/1M tokens).
In conclusion, Phi-3.5-mini-instruct is more expensive than GPT OSS 20B.*
* Using a 3:1 ratio of input to output tokens
Model Size
Parameter count comparison
GPT OSS 20B has 17.1B more parameters than Phi-3.5-mini-instruct, making it 450.0% larger.
Context Window
Maximum input and output token capacity
GPT OSS 20B accepts 131,072 input tokens compared to Phi-3.5-mini-instruct's 128,000 tokens. Phi-3.5-mini-instruct can generate longer responses up to 128,000 tokens, while GPT OSS 20B is limited to 32,768 tokens.
License
Usage and distribution terms
GPT OSS 20B is licensed under Apache 2.0, while Phi-3.5-mini-instruct uses MIT.
License differences may affect how you can use these models in commercial or open-source projects.
Apache 2.0
Open weights
MIT
Open weights
Release Timeline
When each model was launched
GPT OSS 20B was released on 2025-08-05, while Phi-3.5-mini-instruct was released on 2024-08-23.
GPT OSS 20B is 12 months newer than Phi-3.5-mini-instruct.
Aug 5, 2025
1.1 years ago
11mo newerAug 23, 2024
2.0 years ago
Knowledge Cutoff
When training data ends
Neither model specifies a knowledge cutoff date.
Unable to compare the recency of their training data.
Provider Availability
GPT OSS 20B is available from Novita, Fireworks, Groq, OpenAI. Phi-3.5-mini-instruct is available from Azure.
GPT OSS 20B
Phi-3.5-mini-instruct
Outputs Comparison
Judge for yourself.
Run your own prompts against GPT OSS 20B and Phi-3.5-mini-instruct side-by-side, then vote on the output you prefer.
FAQ
Common questions about GPT OSS 20B vs Phi-3.5-mini-instruct.