OpenAI's open-weight reasoner against DeepSeek's long-context bargain.
GPT-OSS 120B is OpenAI's open-weight model, built to reason step by step and to use tools. DeepSeek V4 Flash is the budget coder with an enormous window. Both are text-only, both support tools, and both are covered by zero-retention terms.
GPT-OSS 120B is a 117B-parameter model with 5B active per token, a 128k window and a $0.60 upstream price. DeepSeek V4 Flash is a 284B-parameter model with 13B active, a full million-token window and a $0.18 price. One is tuned for deliberation; the other is tuned for volume.
At a glance
| Spec | GPT-OSS 120B | DeepSeek V4 Flash |
|---|---|---|
| Maker | OpenAI | DeepSeek |
| Parameters | 117B | 284B |
| Active per token | 5B | 13B |
| Context window | 128k (95,000 words) | 1M (750,000 words) |
| Upstream price / MTok | $0.60 | $0.18 |
| Image and video input | No | No |
| Tool use | Yes | Yes |
| Zero data retention | Yes | Yes |
| License | Apache 2.0 | MIT |
| Good at | Reasoning and agent work | Coding and agents |
Where GPT-OSS 120B pulls ahead
- Step-by-step reasoning: GPT-OSS is explicitly built to think through a problem, and 5B active parameters keep that reasoning fast.
- Tool-calling workflows where predictable reasoning traces matter more than raw context length.
- OpenAI-style behaviour and instruction following, which some teams prefer for agent scaffolding.
Where DeepSeek V4 Flash pulls ahead
- Context: one million tokens versus 128k — roughly eight times more text in a single conversation.
- Price: $0.18 versus $0.60 per million tokens, making DeepSeek about 3.3x cheaper.
- Coding at scale and document work where the full project or archive must stay in view.
The price difference
GPT-OSS 120B costs $0.60 per million tokens against $0.18 for DeepSeek V4 Flash — about 3.3x more. On UsingOpen you can chat with both for free inside the daily limit, so the rate is a fair proxy for how expensive each model is to run rather than a bill you pay here. Multiply it by your monthly token volume if you are comparing API access elsewhere.
Which should you choose?
GPT-OSS 120B is the pick when the problem needs careful reasoning and the material fits inside 128k tokens. It is not the model for a whole repository or a year of documents, and its price is three times DeepSeek's.
DeepSeek V4 Flash wins on context and cost. If your task is code generation, log analysis or summarising long archives, the million-token window and $0.18 rate make it the practical choice. Neither model can read an image, so a visual task needs a third option.
Chat with GPT-OSS 120B free · Chat with DeepSeek V4 Flash free
Frequently asked questions
Which has the larger context window, GPT-OSS 120B or DeepSeek V4 Flash?
GPT-OSS 120B is listed at 128k (95,000 words); DeepSeek V4 Flash is listed at 1M (750,000 words). DeepSeek V4 Flash can hold more in one conversation, which matters for long codebases, archives and multi-hour agent runs.
Can GPT-OSS 120B or DeepSeek V4 Flash read images?
Neither model accepts images — both are text-only. A visual task needs a multimodal model such as Qwen3.8 Flash, GLM 5.3 Flash or Gemma 4 instead.
Is GPT-OSS 120B or DeepSeek V4 Flash better for coding?
Both are tuned for coding or agent work: GPT-OSS 120B for reasoning and agent work, DeepSeek V4 Flash for coding and agents. The faster way to choose is to send the same real task to both in Compare mode and read the answers; the spec sheet cannot settle it.
Which is cheaper, GPT-OSS 120B or DeepSeek V4 Flash?
DeepSeek V4 Flash is listed at $0.18 per million tokens against $0.60 for GPT-OSS 120B — about 3.3x cheaper. Both are free to chat with on UsingOpen inside the daily limit when live; the rates matter if you are comparing what API access would cost.
Can I chat with GPT-OSS 120B and DeepSeek V4 Flash for free?
Yes. Both are selectable on UsingOpen without an account when they are live, and each user gets 10 free prompts per day. A model paused for capacity is unavailable until it returns; the picker shows live status. History stays on your device, and Compare mode can send one prompt to both models side by side.
Does either model accept images?
No. GPT-OSS 120B and DeepSeek V4 Flash are both text-only models. If you need image or video input, choose a multimodal model such as Qwen3.8 Flash, GLM 5.3 Flash or Gemma 4.
Which is cheaper for long documents?
DeepSeek V4 Flash, by a wide margin. It costs $0.18 per million tokens against $0.60 for GPT-OSS 120B, and its window is one million tokens versus 128k. A single long document may not even fit in GPT-OSS, which makes the price comparison moot for very large inputs.
Related comparisons
- DeepSeek V4 Flash vs Qwen3.8 Flash — The cheapest serious coder against Alibaba's fast multimodal all-rounder.
- GLM 5.3 Flash vs DeepSeek V4 Flash — The site's default all-rounder against the cheapest heavy hitter.
- Kimi K3 vs DeepSeek V4 Pro — Two flagships: Moonshot's multimodal giant against DeepSeek's full-strength V4.