Chat with DeepSeek V4 Pro for free
DeepSeek V4 Pro delivers powerful open-weight reasoning at a fraction of the cost of comparable proprietary models. Start typing, no sign-up needed.
See how DeepSeek V4 Pro thinks
Pick a task and watch a sample answer stream in. Open the same prompt in Chatday when you’re ready.
The bug is in the arrow body: u.id = id assigns instead of compares, so the callback returns the assigned value and .find never matches the way you expect.
Fix it with a strict comparison:
Use === to compare. A single = is assignment, which is why you saw undefined.
What makes DeepSeek V4 Pro stand out
DeepSeek V4 Pro specifications
| Provider | DeepSeek |
| Model family | DeepSeek V4 series |
| Context window | 1,000,000 tokens |
| Max output | 384,000 tokens |
| Modality | Text · Code |
| Input price | $0.43 / 1M tokens |
| Output price | $0.87 / 1M tokens |
| Tool / function calling | Yes |
| Vision | No |
| Streaming | Yes |
| Available in Chatday | Free & Pro |
Pricing shown for reference; usage is included in your Chatday plan.
DeepSeek V4 Pro vs other top models
| Model | Context | Best at | Input price | In Chatday |
|---|---|---|---|---|
| DeepSeek V4 Pro | 1M | Open-weight reasoning | $0.43/M | Free |
| Claude Opus 4.8 | 1M | Frontier coding | $5/M | Free |
| GPT-5.5 | 1M | Flagship reasoning | $5/M | Free |
| Gemini 3.1 Pro | 1M | Multimodal | $2/M | Free |
DeepSeek V4 Pro questions
Other models
Claude Opus 4.8
Claude Opus 4.8 is Anthropic's strongest model for coding, agentic tasks and enterprise work, with a 1M-token context window.
GPT-5.5
GPT-5.5 is OpenAI's flagship model for hard, multi-step reasoning, coding and tool use, the default when problems get genuinely difficult.
Gemini 3.1 Pro
Gemini 3.1 Pro is natively multimodal across text, image, audio and video, with the largest context window available and fast, fresh answers.
Chat with DeepSeek V4 Pro and switch models any time.
One subscription, every leading model. Start free in the Chatday web app.