When was Claude Fable 5.1 released?

Anthropic released Claude Fable 5.1 on 1 Sep 2026. It is available through the Opper gateway.

Does Claude Fable 5.1 support zero data retention?

With abuse monitoring, yes. On Anthropic, Azure, Google Cloud through the Opper gateway, prompts and outputs are not used for training and are kept only for abuse monitoring.

Where is Claude Fable 5.1 hosted?

Claude Fable 5.1 runs on US hosting routes through the Opper gateway.

Is Claude Fable 5.1 trained on prompts and outputs?

No. Every hosting route for Claude Fable 5.1 is configured so customer prompts and outputs are not used to train models by default.

Is a GDPR DPA available for Claude Fable 5.1?

Yes. A GDPR Data Processing Agreement is available on at least one route serving Claude Fable 5.1. Contact hello@opper.ai to receive it.

Claude Fable 5.1

by Anthropic

Released 39 days after Claude Opus 5 · All Anthropic releases

Claude Fable 5.1 arrived on September 1, 2026 as the successor to Claude Fable 5 at the top of Anthropic's generally available lineup. It is the same model as Claude Mythos 5.1, which Anthropic distributes only through trusted access programs with safeguards tailored to vetted cybersecurity and life sciences work, so Fable 5.1 is the broadly available form of that model. It keeps the 1 million token context window and 128K output ceiling, with image input, PDF handling, tool use, structured output, and adaptive thinking that scales effort to the task. The release is mostly about agentic depth. Anthropic reports 55.8% on Terminal-Bench 4.0 against 42.0% for Fable 5, 52.6% on Terminal-Bench-Science 0.1 against 24.7%, 31.4% on AutomationBench against 17.1%, 73.4% on CursorBench 3.2.0, 41.7% on the strict OSWorld 2.0 computer-use setting, and 60.9% on Humanity's Last Exam without tools. Anthropic also cites a large gain on its contract redlining benchmark and describes the model as steadier than Fable 5 through long stretches of unattended work. Fable 5.1 suits long multi-step engineering sessions, research-grade analysis, and agents that operate terminals and computers over many hours. Its cybersecurity safeguards now block about 60% fewer false positives than before, and the model can be used to find software vulnerabilities, though not to develop exploits.

Call Claude Fable 5.1 on Opper with the OpenAI SDK. Sign up without a credit card. Get started

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Key info

Input

Output

Features

Context window

Max output

128K

Input price

$10.00 /1M$0.25 cache read · $12.50 write

Output price

$50.00 /1M

Released

1 Sep 2026

US residency available
Zero data retention with abuse monitoring
No training by default
GDPR DPA available

Available routes

Claude Fable 5.1 runs on 3 different routes through the Opper gateway. Compare residency, zero data retention and training posture at a glance, with full data-handling detail per route below.

Provider	Region	Training	Input	Output	Cache read
Anthropic	US	No	$10.00	$50.00	$0.25$12.50 write
Azure	Multi	No	$10.00	$50.00	$0.25$12.50 write
Google Cloud	Multi	No	$10.00	$50.00	$0.25$12.50 write

Uptime and availability

Claude Fable 5.1 runs on 3 independently monitored routes through the Opper gateway. A direct integration leaves you on one of them, the gateway serves whichever is healthy.

100%effective uptime, last 30 days

Averaged across these routes on their own, a single provider reached 94.30% over the same window.

Daily status through the gateway, which serves each request from whichever route is healthy.

3 monitored providers serve Claude Fable 5.1.

Measured over the last 30 days from each provider's official status feed via StatusGator. Refreshed hourly. See uptime for every provider Opper monitors.

Data handling per route

Each route hosting Claude Fable 5.1 has its own privacy posture, residency, and GDPR terms. Postures are maintained by Opper with a last-verification timestamp.

Anthropic — United States🇺🇸

Zero data retention with abuse monitoring: prompts and outputs are kept for abuse monitoring only, for a window the provider does not state, and are not used for training. No training on customer data. US; SCCs; DPA available.

Zero data retention: With abuse monitoring, window not stated.
Training: No training on customer data.
Logging: Abuse monitoring
Abuse monitoring: On by default, holds flagged content, 730 days, a person can view samples
Caching: Content cached for replay
GDPR DPA: DPA available
Transfer mechanism: SCCs

Azure — Multi-region

Zero data retention with abuse monitoring: nothing is logged or used for training; content flagged by abuse monitoring is held for review. No training on customer data. GLOBAL; SCCs; DPA available.

Zero data retention: With abuse monitoring, flagged content held.
Training: No training on customer data.
Logging: None
Abuse monitoring: On by default, holds flagged content, 730 days, a person can view samples
Caching: Content cached for replay
GDPR DPA: DPA available
Transfer mechanism: SCCs

Google Cloud — Multi-region

Zero data retention: With abuse monitoring, window not stated.
Training: No training on customer data.
Logging: Abuse monitoring
Abuse monitoring: On by default, holds flagged content, 90 days, a person can view samples
GDPR DPA: DPA available
Transfer mechanism: SCCs

Benchmarks

Independent benchmark scores — composite indices for reasoning, coding, and math, plus individual eval scores where available.

Global rank#4 of 652 LLMs

TierFrontier

Output speed65 tok/s

First token123.03s

Intelligence Index53.4

Coding Index81.6

Reasoning & knowledge

GPQA Diamond

94%

Humanity's Last Exam

59%

Long-context reasoning

85%

Coding

SciCode

63%

See full leaderboard →Benchmarks via Artificial Analysis · View on AA

Get started

Call Claude Fable 5.1 through the Opper gateway with one API key. Opper is drop-in compatible with the OpenAI, Anthropic and Google AI SDKs.

Claude Fable 5.1 is a premium model on Opper. Sign up needs no credit card: you get an API key straight away and the free models work in the playground and the API. Add a card to use premium models, pay-as-you-go with no minimum.

Set it up with your agent

Copy this and paste it into a coding agent like Claude Code, Cursor or Codex and it'll wire up Opper for you.

Or call it directly

1import OpenAI from "openai";
2
3const client = new OpenAI({
4  apiKey: process.env.OPPER_API_KEY,
5  baseURL: "https://api.opper.ai/v3/compat",
6});
7
8const completion = await client.chat.completions.create({
9  model: "claude-fable-5-1",
10  messages: [{ role: "user", content: "Hello" }],
11});
12console.log(completion.choices[0].message.content);