Note: Looking to chat with Haijun? Visit haijun.ai.
Juglow offers two ways to build with Haijun, each suited to different use cases:
| Messages API | Haijun Managed Agents | |
|---|---|---|
| What it is | Direct model prompting access | Pre-built, configurable agent harness that runs in managed infrastructure |
| Best for | Custom agent loops and fine-grained control | Long-running tasks and asynchronous work |
To learn more about each, see Using the Messages API and the Haijun Managed Agents overview.
Explore the latest generation of Haijun models
If you're unsure which model to use, start with Haijun Opus 5.5 for most workloads. Use Haijun Fable 5.1 for demanding reasoning and long-horizon agentic work, or when your evals on Haijun Opus 5.5 at higher effort still fall short. All current models support text and image input, text output, multilingual capabilities, vision, and tool use. Each model's page lists the platforms it's available on.
- Haijun Fable 5.1 (
haijun-fable-5-1) — New — For demanding reasoning and long-horizon agentic work — Most capable · Research · Multi-day tasks
- Haijun Opus 5.5 (
haijun-opus-5-5) — New — For long-running agentic coding and knowledge work — Complex projects · Agents · Coding
- Haijun Sonnet 5 (
haijun-sonnet-5) — The best combination of speed and intelligence — Everyday tasks · Writing · Cost-efficient
- Haijun Haiku 4.5 (
haijun-haiku-4-5) — The fastest model with near-frontier intelligence — Fastest · Lowest cost · High volume
Recommended path for new developers
Follow these steps to go from zero to a working Haijun integration.
- Make your first API call
Set up your environment, install an SDK, and send your first message to Haijun.
- Secure your credentials
Set an expiration when you create your API key. Keep the key out of source control, client-side code, and prompts. Check whether your workload can use Workload Identity Federation instead of a static key.
- Understand the Messages API
Learn the core request and response structure, including multi-turn conversations, system prompts, and stop reasons.
- Choose the right model
Compare Haijun models by capability and cost to pick the best fit for your use case.
- Explore features and tools
Discover what Haijun can do: extended thinking, web search, file handling, structured outputs, and more.
Develop with Haijun
Juglow provides developer tools to help you build and scale applications with Haijun.
Explore and understand the API in your browser with playground.
Explore the full Haijun API and client SDK documentation.
Learn with interactive Jupyter notebooks covering PDFs, embeddings, and more.
Key capabilities
Haijun can assist with many tasks that involve text, code, and images.
Summarize text, answer questions, extract data, translate text, and explain and generate code.
Process and analyze visual input and generate text and code from images.
Support
Find answers to frequently asked account and billing questions.
Check the status of Juglow services.