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Key Takeaways

  • Mythos-class flagship: Claude Fable 5 hits SOTA on nearly all tested benchmarks, with standout software engineering and vision capabilities
  • Long-running + self-evolving: Supports long-running, asynchronous execution; self-updates skills based on learnings and builds its own harnesses for sustained complex work
  • Strong vision understanding: Reads diagrams, charts, and tables in files and PDFs — ideal for research and document-heavy work
  • Pricing matches official: claude-fable-5 is live on APIYI at $10 input / $50 output per 1M tokens
  • ⚠️ 30-day data retention compliance: Because of their advanced capabilities, Fable 5 and Mythos 5 retain inputs and outputs for 30 days for serious-abuse detection — read the compliance note below

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Background

In June 2026, Anthropic released its next-gen flagship Claude Fable 5, alongside the more capable, vetted-customers-only Mythos 5. Anthropic positions Fable 5 as next-generation intelligence for knowledge work and coding, reaching SOTA on nearly all tested benchmarks with exceptional software engineering and vision. Unlike previous models, Fable 5 and Mythos 5 are Mythos-class models: because they are more capable and carry higher potential for misuse, Bedrock and Anthropic enforce additional high-risk misuse checks and a 30-day data retention compliance requirement for both models. This is essential context before adopting Fable 5. claude-fable-5 is now live on APIYI at pricing identical to the official rates.

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Data Retention & Compliance (Important)

30-day data retention applies to Fable 5 and Mythos 5With Anthropic’s release of Claude Fable 5 and Mythos 5, and because of these advanced models’ capabilities, Bedrock and Anthropic are enforcing additional checks for high-risk misuse activity. For Fable 5 and Mythos 5, inputs and outputs will be retained for 30 days to detect serious abuse.
  • Default access: Retained data is accessed only by automated safety systems; Anthropic human review happens only when those systems flag potential harm.
  • Human review scope: Anthropic reviewers may access inputs and outputs associated with the relevant account, but only to the extent needed to complete the review.
  • Cross-account review: If traffic from multiple accounts is flagged for the same prohibited activity, Anthropic may review that flagged traffic together in a single review.
Retention is by AWS / Anthropic, not APIYI: the 30-day retention above happens on AWS Bedrock and Anthropic’s official side (passed through to Anthropic for abuse detection). APIYI itself retains no data — it is a pure transparent proxy that only forwards requests. Also, only Fable 5 and Mythos 5 are subject to this retention; all other Claude models (e.g. Opus 4.8 / Sonnet 4.6) do not retain data.
Further reading (copy into your browser):
  • Anthropic on human review and data retention: support.claude.com/en/articles/15425996
  • AWS official blog (Fable 5 on AWS): aws.amazon.com/blogs/aws/anthropic-claude-fable-5-on-aws-mythos-class-capabilities-with-built-in-safeguards-now-available/

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Deep Dive

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Core Features

Near-universal SOTA

State-of-the-art on nearly all tested benchmarks, with standout software engineering and vision

Long async execution

Long-running, asynchronous execution for sustained complex Agent workflows

Self-updating skills

Self-updates skills based on learnings and develops its own harnesses, cutting setup cost

Strong vision

Understands diagrams, charts, and tables in files and PDFs for research-heavy work

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Built-in Safety Guardrails

Fable 5 ships with guardrails: harmful prompts in high-risk domains (cybersecurity, biology, chemistry, health) are automatically redirected (fallback) to Claude Opus 4.8. The fully unrestricted Mythos 5 is available only to a small group of vetted customers.
On billing: when a harmful prompt triggers fallback to Opus 4.8, it is charged at Opus rates; mixed-token requests are charged Fable rates initially, then Opus rates for subsequent tokens after fallback. Final billing follows live platform data.

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Specs

ParameterSpec
Model IDclaude-fable-5
Model tierMythos-class
Data retentionInputs/outputs retained 30 days (abuse detection)
Safety fallbackHigh-risk harmful prompts fall back to claude-opus-4-8
API formatsOpenAI-compatible / Anthropic native
ChannelsAnthropic API, AWS Bedrock, APIYI

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Usage

  1. Complex software engineering: repo-scale coding, cross-file refactors, architecture decisions
  2. Long-horizon Agent tasks: long async execution and self-updating research/code agents
  3. Document & vision-heavy work: research analysis over PDFs with charts, tables, and diagrams
  4. Hard reasoning tasks: leverage the judgment of a Mythos-class flagship

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Code Examples

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OpenAI format

from openai import OpenAI

client = OpenAI(
    api_key="your-apiyi-key",
    base_url="https://api.apiyi.com/v1"
)

response = client.chat.completions.create(
    model="claude-fable-5",
    messages=[
        {
            "role": "user",
            "content": "Review this codebase architecture and flag risks and refactor suggestions."
        }
    ]
)

print(response.choices[0].message.content)

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Anthropic native format

import anthropic

client = anthropic.Anthropic(
    api_key="your-apiyi-key",
    base_url="https://api.apiyi.com"
)

message = client.messages.create(
    model="claude-fable-5",
    max_tokens=8192,
    messages=[
        {
            "role": "user",
            "content": "Trace the root cause of this production bug step by step and propose a fix."
        }
    ]
)

print(message.content[0].text)

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Best Practices

  1. Compliance first: brief your team on the 30-day data retention requirement before adoption; handle sensitive data per your internal compliance policy.
  2. Pick by task: use claude-fable-5 for hard coding/Agent tasks; for cost-sensitive routine work, consider claude-opus-4-8 or the Sonnet line.
  3. Leverage vision: feed chart-heavy PDFs directly for research and document parsing.

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Pricing & Availability

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Pricing

ItemClaude Fable 5Note
Input$10 / 1M tokensMatches official
Output$50 / 1M tokensMatches official
APIYI claude-fable-5 pricing matches Anthropic’s official rates exactly ($10 / $50 per 1M tokens). Final billing follows live platform data.

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Stack with Top-up Promotions

Combine with APIYI top-up bonus promotions to lower your effective cost — see docs.apiyi.com/faq/recharge-promotions.

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How to Access

APIYI platform:
  • Website: apiyi.com
  • OpenAI format: https://api.apiyi.com/v1
  • Anthropic native format: https://api.apiyi.com
  • Model name: claude-fable-5

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Summary & Recommendations

Claude Fable 5 is Anthropic’s new Mythos-class flagship — SOTA across software engineering and vision, with long async execution and self-updating skills. claude-fable-5 is live on APIYI at official pricing ($10/$50). Read before adoption:
  • 30-day data retention: Fable 5 and Mythos 5 retain inputs/outputs for 30 days for abuse detection; by default only automated safety systems access it, with human review only when potential harm is flagged. Retention happens on the AWS / Anthropic side — APIYI is a pure transparent proxy and retains no data; other Claude models are unaffected.
  • Safety fallback: harmful prompts in high-risk domains fall back to Opus 4.8 and are charged at Opus rates.
Sources: Anthropic official note (support.claude.com/en/articles/15425996), AWS official blog (published June 2026). APIYI pricing follows live platform data. Retrieved: June 10, 2026.