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Today marks a historic moment: OpenAI released GPT-OSS-120B and GPT-OSS-20B, their first open-weight models since GPT-2 in 2019. We’re bringing you the most powerful one: GPT-OSS-120B, live on Chat-O as a Balanced tier model. This release was soon followed by GPT-5, and the open-weight landscape has continued evolving with models like GLM-5.1 and the complete Z-AI GLM family.
This isn’t your typical open-source model. GPT-OSS-120B delivers state-of-the-art performance:
GPT-OSS-120B uses a Mixture-of-Experts (MoE) architecture with 117B total parameters but only 5.1B active per token. This design achieves GPT-4-class reasoning while keeping inference costs comparable to much smaller models. The MoE approach routes each token to the most relevant expert sub-networks, enabling specialized knowledge without full parameter activation.
| Spec | GPT-OSS-120B | GPT-OSS-20B | GPT-5 (proprietary) |
|---|---|---|---|
| Total params | 117B | 20B | Unknown |
| Active per token | 5.1B | 5.1B | Unknown |
| License | Apache 2.0 | Apache 2.0 | Proprietary |
| Focus | General reasoning | Lightweight | General purpose |
GPT-OSS-120B doesn’t just talk the talk:
While others read the announcement, you’re already chatting with GPT-OSS-120B. This is why we built Chat-O—instant access to breakthrough AI.
The Chat-O Advantage:
Since this launch, we’ve added many more models. The Kimi K2.6 brought multi-agent capabilities, and the Complete Kimi Family now spans from lightweight to frontier models. For the latest in open-weight reasoning, check our GLM-5.2 release.
GPT-OSS-120B excels at complex tasks:
GPT-OSS-120B shines in real-world deployments where transparency matters: regulated industries needing audit trails, research teams studying model behavior, and enterprises building custom fine-tuned pipelines. Its Apache 2.0 license means no restrictions on commercial use, modification, or redistribution—a stark contrast to many “open” models with restrictive licenses.
The smaller GPT-OSS-20B shares the same 5.1B active parameters per token but with only 20B total, making it significantly faster and cheaper while retaining strong reasoning for its size. It’s ideal for high-throughput applications where GPT-OSS-120B would be overkill.
Transparency Meets Power: Unlike proprietary models, GPT-OSS-120B is completely open-weight under Apache 2.0. Enterprise-grade performance with full transparency.
Multi-Model Magic: Compare insights from GPT-OSS-120B, Claude 3.7, and Gemini 2.5 in one conversation. See how different reasoning approaches tackle problems.
The open-weight landscape has since evolved significantly. For a comparison of the latest frontier models, see our GLM-5.2 vs Kimi K3 comparison. While GPT-OSS-120B remains a strong open-weight choice, newer models like Kimi K3 push parameter counts to 2.8T and context windows to millions of tokens.
Ready to experience OpenAI’s most powerful open-weight model? Jump into Chat-O and start a conversation with GPT-OSS-120B.
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Because GPT-OSS-120B is open-weight, users with sufficient hardware can self-host it for complete data sovereignty. This appeals to enterprises with strict data residency requirements or teams building custom AI pipelines. The MoE architecture’s 5.1B active parameters mean it can run on relatively modest hardware compared to dense 120B models, though you’ll need substantial VRAM for the full 117B parameter set.
GPT-OSS-120B is live now, but this is just the beginning. Our team continuously monitors AI releases worldwide, ensuring Chat-O users get first access to every breakthrough model.
Ready to think bigger? Start your Chat-O journey today and discover what’s possible with the world’s most advanced AI models.
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