Chat with GPT-5.1 Instant for free
GPT-5.1 Instant is optimized for instant responses in high-volume workflows where latency matters more than maximum depth. Start typing, no sign-up needed.
See how GPT-5.1 Instant 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 GPT-5.1 Instant stand out
GPT-5.1 Instant specifications
| Provider | OpenAI |
| Model family | GPT-5 series |
| Context window | 128,000 tokens |
| Max output | 16,384 tokens |
| Modality | Text · Code |
| Input price | $1.25 / 1M tokens |
| Output price | $10 / 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.
GPT-5.1 Instant vs other top models
| Model | Context | Best at | Input price | In Chatday |
|---|---|---|---|---|
| GPT-5.1 Instant | 128K | Low latency | $1.25/M | Free |
| Claude Opus 4.8 | 1M | Frontier coding | $5/M | Free |
| Gemini 3.1 Pro | 1M | Multimodal | $2/M | Free |
| Grok 4 | 1M | Realtime | $0.2/M | Free |
GPT-5.1 Instant 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 GPT-5.1 Instant and switch models any time.
One subscription, every leading model. Start free in the Chatday web app.