Claude Fable 5.2 API

Claude Fable 5.2 is Anthropic's model released on 9 November 2026, the successor to Claude Fable 5.1. Like its predecessor it is the generally available version of a Mythos model (here Mythos 5.2) with extra safeguards around cybersecurity and biology. It has a 1,000,000-token context window, returns up to 128K output tokens and accepts text and images. Anthropic lowered list pricing with this version, so on Jantaris Fable 5.2 costs less than Fable 5.1.

Best for

• Hard analysis and research where mistakes are expensive
• Long-running autonomous agents with many tools
• Large refactors and reviews of big codebases
• Tasks where Claude Opus 5.5 fails your own tests

How to connect

OpenAI SDK with the Jantaris base URL:

from openai import OpenAI

client = OpenAI(base_url="https://jantaris.com/v1", api_key="sk-jt-...")
resp = client.chat.completions.create(
    model="claude-fable-5.2",
    messages=[{"role": "user", "content": "Write a database migration plan and the risk of each step."}],
)
print(resp.choices[0].message.content)

It also works with the Anthropic SDK and Claude Code via /v1/messages - see the Claude Code docs.

FAQ

How much does Claude Fable 5.2 cost per million tokens?

On Jantaris Fable 5.2 costs $7.56 / $37.80 per 1M tokens. Thinking is billed as output tokens, so measure usage on a few real tasks before moving a whole workflow.

How is it different from Claude Fable 5.1?

It is the newer version with lower list pricing at Anthropic. Fable 5.1 stays in the catalog ($9.45 / $47.25 per 1M tokens) if your prompts are tuned for it.

Does Claude Fable 5.2 work with Claude Code?

Yes. Point ANTHROPIC_BASE_URL at https://jantaris.com, use your sk-jt- key and set the model to claude-fable-5.2.

How to call Claude Fable 5.2 via API

from openai import OpenAI

client = OpenAI(base_url="https://jantaris.com/v1", api_key="sk-jt-...")
resp = client.chat.completions.create(
    model="claude-fable-5.2",
    messages=[{"role": "user", "content": "Write a haiku about Baltic amber."}],
)
print(resp.choices[0].message.content)

curl https://jantaris.com/v1/chat/completions \
  -H "Authorization: Bearer $JANTARIS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model": "claude-fable-5.2", "messages": [{"role": "user", "content": "Write a haiku about Baltic amber."}]}'

import OpenAI from "openai";

const client = new OpenAI({ baseURL: "https://jantaris.com/v1", apiKey: process.env.JANTARIS_API_KEY });
const resp = await client.chat.completions.create({
  model: "claude-fable-5.2",
  messages: [{ role: "user", content: "Write a haiku about Baltic amber." }],
});
console.log(resp.choices[0].message.content);

export ANTHROPIC_BASE_URL=https://jantaris.com
export ANTHROPIC_AUTH_TOKEN=sk-jt-...
export ANTHROPIC_MODEL=claude-fable-5.2
claude