LongCat-2.0 API Platform Quick Start (Official Quick Start + Chat Completions Reference + Pricing)

One-sentence takeaway

This official documentation gets you an API key in five minutes, lets you connect LongCat-2.0 to any client using either OpenAI- or Anthropic-compatible formats, and explains the 1M context / 128K maximum output parameters and the pricing structure in which cache hits are not billed.

Use cases

• Suitable tasks: Connect LongCat-2.0 to a self-hosted application, script, IDE plugin, or Agent framework; evaluate costs; configure cache optimization for Agent loops

• Unsuitable tasks: Multimodal input (the API accepts text only, and the official documentation explicitly says "Text input only"); model parameter tuning not publicly disclosed by the official source

• Applicable model version: LongCat-2.0 (currently the only model sold on the API platform)

• Applicable clients, Agents, or APIs: Any OpenAI-compatible client (base_url pointing to /openai), any Anthropic-compatible client (base_url pointing to /anthropic), OpenAI/Anthropic SDKs, cURL

• Recommended reasoning tier and parameters: temperature 0~1; max_tokens capped at 131072 (128K); enable thinking with {"type":"enabled"} and disable it with {"type":"disabled"} (enabled by default); cached-input billing is far lower than uncached-input billing

Ready-to-use content

1. Get an API key

1. Visit https://longcat.chat/platform and create an account.

2. After signing in, open the API Keys page and create a key manually (it is shown only once at creation, so save it immediately).

2. Endpoints and model

Model name: LongCat-2.0 (available in both OpenAI and Anthropic formats).

Limitations: Maximum context is 1M tokens and maximum output is 128K tokens (max_tokens capped at 131072). Requests beyond the limit return HTTP 429; clients should use exponential-backoff retries.

3. OpenAI-format request (Python)

from openai import OpenAI

client = OpenAI(
    api_key="YOUR_APP_KEY",
    base_url="https://api.longcat.chat/openai"
)

response = client.chat.completions.create(
    model="LongCat-2.0",
    messages=[{"role": "user", "content": "Hello!"}],
    max_tokens=1000
)
print(response.choices[0].message.content)

4. Anthropic-format request (Python)

from anthropic import Anthropic

client = Anthropic(
    api_key="YOUR_APP_KEY",
    base_url="https://api.longcat.chat/anthropic",
    default_headers={
        "Content-Type": "application/json",
        "Authorization": "Bearer YOUR_APP_KEY",
    }
)

response = client.messages.create(
    model="LongCat-2.0",
    max_tokens=1000,
    messages=[{"role": "user", "content": "Hello!"}]
)
print(response.content[0].text)

5. Key Chat Completions parameters (official API reference)

POST https://api.longcat.chat/openai/v1/chat/completions
Authorization: Bearer YOUR_API_KEY

body:
  model: "LongCat-2.0"
  messages: [{role: "system"|"user"|"assistant", content: "<plain text>"}]
  stream: true|false          # SSE streaming supported
  max_tokens: 131072          # 128K limit
  temperature: 0 ~ 1
  top_p: <nucleus sampling parameter>
  thinking: {"type": "enabled"} | {"type": "disabled"}   # Explicitly toggle thinking mode

The response includes reasoning_content and usage.completion_tokens_details.reasoning_tokens (the number of reasoning tokens), which can be used to track reasoning overhead.

6. Pricing (Pay-As-You-Go, ¥/1M tokens)

Note: The official source also sells token packages (a post from the official X account on 2026-08-03: 50 million tokens for $4.9, with a limited-time 67% discount; a $1.9 starter package for new users). Prices are subject to the platform invoice.

Raw data and verification notes

• The endpoints, parameters, and pricing above were transcribed directly from the official documentation pages (collected on 2026-08-18).

• Community testing (r/vibecoding) confirmed that "cached input is not billed; only uncached input and output are charged," consistent with the official pricing language. However, the actual OpenRouter (AtlasCloud) transaction price (weighted average input price of $0.03872/M) is significantly below the list price, showing that the cache discount has a substantial effect in real Agent loops.

• An AlphaSignal article (2026-07-01) cited an earlier list price of $0.69/$2.78 per 1M, which differs from the current official ¥5/¥20 figures; pay attention to the version date when citing it.

Scope and limitations

• This document covers only the official direct channel (api.longcat.chat). Model IDs, prices, and free quotas on third-party channels such as OpenRouter, Nous Portal, and opencode are subject to each platform.

• The API accepts text only and does not support image, audio, or video input.

• The thinking parameter has a significant effect on output token count (reasoning tokens are included in output billing). To control costs, use {"type":"disabled"}.