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 | $0.66 / 1M tokens |
| Output price | $1.98 / 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 | $0.66/M | Free |
| Grok 4.6 | 500K | Agentic reasoning | $2/M | Free |
| Claude Opus 5 | 1M | Frontier agents | $5/M | Free |
| GPT-5.6 | 1.1M | Flagship reasoning | $2/M | Free |
DeepSeek V4 Pro questions
Other models
Grok 4.6
Grok 4.6 is xAI's flagship for long agentic runs, with self-checking on multi-step tasks and strong coding at half frontier prices.
Claude Opus 5
Claude Opus 5 is Anthropic's strongest Opus model: hybrid reasoning for long-running agents, serious coding and computer use.
GPT-5.6
GPT-5.6 is OpenAI's newest flagship for hard, multi-step reasoning, coding and tool use, the default when problems get genuinely difficult.
Chat with DeepSeek V4 Pro and switch models any time.
One subscription, every leading model. Start free in the Chatday web app.