Claude Fable 5 Is Live on BUZZ: Model ID, Pricing, and Migration Notes

Claude Fable 5 — the first model in Anthropic's new Claude 5 family and its most capable generally available model — is now routable through BUZZ AI Gateway. No new account, no new endpoint, no new key. Change the model string to claude-fable-5 and you are on the frontier. This post covers the exact identifier, where Fable 5 sits in the lineup, the pay-per-token price, and how prompt caching behaves when you switch.

Published 2026-06-09 · Reading time ~6 min

Where Fable 5 sits

Claude Fable 5 is the opening model of the Claude 5 generation. It belongs to a new Mythos-class tier that sits above Claude Opus in capability — the first time Anthropic has shipped a generally available model above the Opus line. If you have been reaching for Opus 4.8 on the hardest reasoning, agentic, and analysis work, Fable 5 is the next step up.

One point of naming that trips people up: Fable 5 and Mythos 5 are the same underlying model. Fable 5 is the generally available version and carries additional safety measures around dual-use capabilities. Mythos 5 is the same model without those measures, available only to approved organizations. For virtually every developer and every request through BUZZ, the model you want is claude-fable-5.

The identifier

The model name is claude-fable-5. As with every Claude model, Anthropic uses hyphens, not dots — claude-fable-5.0 or claude.fable.5 will return a 404 model not found. If you see that error after switching, check the string first.

BUZZ exposes Fable 5 on both interfaces it already serves:

• Anthropic Messages at https://buzzai.cc/v1/messages — used by Claude Code and the official anthropic SDK.
• OpenAI-compatible at https://buzzai.cc/v1/chat/completions — used by the openai SDK and anything that speaks the chat.completions schema.

The full live model list is always published at https://buzzai.cc/models. If a name appears there, your key can reach it.

Calling it

Anthropic Messages (curl):

curl https://buzzai.cc/v1/messages \
  -H "x-api-key: $BUZZ_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "content-type: application/json" \
  -d '{
    "model": "claude-fable-5",
    "max_tokens": 1024,
    "messages": [{"role": "user", "content": "Design a rate limiter for a multi-tenant API."}]
  }'

OpenAI SDK (Python) — only base_url and model differ from a stock OpenAI call:

from openai import OpenAI

client = OpenAI(
    base_url="https://buzzai.cc/v1",
    api_key="YOUR_BUZZ_KEY",
)

resp = client.chat.completions.create(
    model="claude-fable-5",
    messages=[{"role": "user", "content": "Design a rate limiter for a multi-tenant API."}],
)
print(resp.choices[0].message.content)

Claude Code — point it at BUZZ once and select Fable 5 like any other model:

export ANTHROPIC_BASE_URL=https://buzzai.cc
export ANTHROPIC_AUTH_TOKEN=YOUR_BUZZ_KEY
# then select claude-fable-5 in Claude Code's model picker

Pricing

Fable 5 is billed pure pay-per-token, with no monthly fee and no minimum spend — the same model that applies to every other model on BUZZ.

Prompt cache reads and writes are billed automatically using Anthropic's official discount multipliers. On a workload with a stable, reused prefix — long system prompts, large tool schemas, retrieved documents — the effective input cost lands far below the headline rate, because most of the prefix is served as cache reads rather than fresh input. See the prompt caching playbook for how to structure requests so the cache actually hits. Because Fable 5 is the priciest model on the menu, prompt caching matters most here — a good cache-hit rate is the difference between a heavyweight model you use freely and one you ration.

Upgrading from Opus 4.8: what changes (almost nothing)

The switch is intentionally boring. Here is the full list of what you touch:

The one thing to watch: cache warm-up

Prompt cache entries are scoped per model. A prefix you cached under claude-opus-4-8 does not carry over to claude-fable-5 — the first request on the new model is a cache miss and pays the full input rate for that prefix. After that first warm-up pass, cache reads resume normally on the new model.

If you swap models mid-session and notice cache_read_input_tokens drop to zero for a request or two, that is expected. It climbs back as the new model's cache fills.

When to reach for Fable 5

Fable 5 is the model you escalate to, not the one you run everything on. It earns its price on genuinely hard work: long multi-step agentic loops that lose the thread on smaller models, deep code refactors across many files, tricky analysis and math, and anything where a wrong answer is expensive. For the bulk of chat, drafting, and routine coding, Claude Sonnet 5 at a fifth of the input price is the right default.

The production pattern that works: default traffic to Sonnet 5, and route only the requests that need it to Fable 5. Because BUZZ uses one key and one endpoint for the whole Claude 5 family, that escalation is a single string in your own code — not a second integration, not a second bill. See the Claude 5 family selection guide for a decision tree.