Hy4 Preview
Overview
Hy4 Preview is an open-weight Mixture-of-Experts language model released by the Tencent Hy Team on August 28, 2026. It is an early Hy4-series release with 770 billion backbone parameters, 49 billion activated parameters per token, and a 1M-token context window. On B.AI, use the model ID hy4-preview.
Key Features
- 770B Sparse MoE Architecture: Uses 78 backbone layers, 256 routed experts and one shared expert per MoE layer, and activates the top eight routed experts plus the shared expert for each token. A separate native MTP layer adds 10B total and 0.7B activated parameters for speculative decoding.
- Long-Context API Limits: Supports a 1M-token context window, up to 960K input tokens, and up to 64K output tokens.
- Preserved Deep Reasoning: Thinking is enabled by default. The API exposes
reasoning_content, which should be returned with the complete assistant message during multi-turn tool workflows. - Agent API Support: Supports structured output, function calling, cached input, and OpenAI Chat Completions, OpenAI Responses, and Anthropic Messages interfaces.
- Productivity-Oriented Validation: In Tencent's blind internal evaluation, 163 experts rated outputs on 203 engineering tasks. Hy4 Preview averaged 2.99/4.00, compared with 2.92 for GLM-5.3 and 2.94 for Kimi K3.
Best Use Cases
- Software Engineering Agents: Long-horizon planning, implementation, debugging, verification, frontend work, and multi-step tool use across large repositories.
- Office and Data Workflows: Cross-document analysis, financial modeling, data analysis, and production of documents, spreadsheets, and presentations.
- Game Development: Playable-prototype generation, game-engine workflows, and iterative refinement over multiple turns.
- Scientific Research: Tool-assisted analysis and problem solving in areas such as AI research, molecular dynamics, condensed-matter physics, and mathematics.
- Private or Customized Deployment: Open-weight deployments that require local serving, quantization, or task-specific fine-tuning and can accommodate the model's substantial compute requirements.
Capabilities and Limitations
| Capability | Description |
|---|---|
| Reasoning | Supports deep reasoning with preserved thinking. The documented reasoning-effort levels are low and high, with high as the default for hy4-preview tool workflows. |
| Creative Writing | Supports general text generation and Chinese content creation. |
| Multimodal | Text input and text output. |
| Response Speed | Tencent has not published a guaranteed generation rate. The official release reports a 31.8% throughput gain from model-assisted inference-system optimization relative to Tencent's internal baseline. |
| Context Window | 1M tokens. |
| Maximum Input | 960,000 tokens. |
| Max Output | 64,000 tokens. |
| Tool Use | Function calling, structured output, automatic tool selection, cached input, and preserved reasoning across tool calls. |
| Multilingual | Tencent documents Chinese and English use. |
Known Limitations
- Tencent identifies this release as an early version of Hy4 rather than a final Hy4 model.
- The official model card reports that Hy4 Preview can spend longer than necessary reasoning through complex tasks and can over-verify its own work.
- Multi-turn tool integrations should preserve and replay the full assistant message, including
reasoning_content; omitting it can degrade the documented continuation workflow. - Hy4 Preview does not support native image, audio, or video understanding.
- Tencent has not published a model-specific knowledge cutoff, guaranteed API throughput, or complete language-support list.
Pricing
| Model | Input (Credits/Token) | Cache Write (Credits/Token) | Cache Read (Credits/Token) | Output (Credits/Token) | Web Search (Credits/Use) |
|---|---|---|---|---|---|
| Hy4 Preview | 0.834 | 0.834 | 0.042 | 2.501 | - |
Pricing note
Prices shown in the documentation are B.AI standard reference prices for base billing purposes. B.AI may provide lower actual usage costs through top-up bonuses and account benefits. Specific prices, bonus Credits, and account benefits are subject to the platform display and final billing records.