Anthropic
Claude Opus 5
From $2.40 per 1M tokens
Chat
Claude Fable 5 — Anthropic's Most Capable Model
Claude Fable 5 is Anthropic's most capable widely released model for the most demanding reasoning and long-horizon agentic coding — 1M context, 128K max output, always-on adaptive thinking, vision input, and standard /v1/chat/completions in one call. Pay-as-you-go pricing in USD.
Claude Fable 5model
claude-fable-5Claude Fable 5 playground
Chat models run on the api.reapi.ai gateway, which has its own console and its own key. Open the console to run Claude Fable 5 through the OpenAI-compatible Chat Completions surface.
What you can build with this model
Real-world workflows and production use cases you can build and ship with this model.
Frontier long-horizon agentic coding
Claude Fable 5 is built for the most demanding agentic work Anthropic's models can do — week-long refactors, codebase-scale migrations, and autonomous runs that must stay coherent across hundreds of steps. Where lighter models drift, Claude Fable 5 holds the plan, verifies its own output, and keeps going.
Read the API docs
The hardest reasoning problems
When a problem sits past what Opus-tier models handle cleanly — deep multi-step reasoning, ambiguous specifications, high-stakes analysis — Claude Fable 5 is the model Anthropic positions above everything else it widely ships. Adaptive thinking is always on, and the effort parameter scales how much reasoning Claude Fable 5 invests in each call, up to max.
Large-context analysis and review
Feed entire codebases, long research packs, multi-file technical material, or full policy documents into a single Claude Fable 5 request. The 1M token context window is billed at standard per-token rates — no long-context premium — so analysis-heavy Claude Fable 5 workflows rarely need chunking.
Pricing
Credit-based — 1 credit = $0.001 USD. Pay only for completed generations.
| Category | Unit | Price |
|---|---|---|
| Tokens | ||
| Input tokens | 1M tokens | $8 |
| Output tokens | 1M tokens | $40 |
Why reAPI
Drop-in access for Anthropic's top tier
Claude Fable 5 speaks OpenAI Chat Completions verbatim. Moving an existing OpenAI integration to Claude Fable 5 is a base URL, an API key, and a model-string change — not a platform rewrite. The same `messages` array, the same streaming format, and the native Anthropic /v1/messages surface is available too for SDK callers that prefer it.
The most capable model Anthropic widely ships
Claude Fable 5 sits a full tier above Claude Opus 4.8 — Anthropic's most capable widely released model, generally available since June 9, 2026. Route the hardest reasoning and the longest agentic runs to Claude Fable 5; send everyday premium coding to Opus-tier models on the same key.
One key across GPT, Claude, and Gemini
A single api.reapi.ai key unlocks Claude Fable 5 alongside GPT-5.5, Claude Opus 4.8, Gemini 3.1 Pro, and every other frontier chat model on the platform. Compare vendors, add fallbacks, and route traffic per call with a configuration change instead of an integration project.
Claude Fable 5 vs Claude Opus 4.8
Claude Fable 5 is the tier above Opus — the most capable model Anthropic widely releases, launched June 9, 2026. Here is how it compares with Claude Opus 4.8, Anthropic's strongest Opus-tier model, based on Anthropic's own documentation.
Capability
Claude Fable 5 on reAPI
Claude Opus 4.8
Capability tier
Anthropic's most capable widely released model — built for the most demanding reasoning and long-horizon agentic work.
Anthropic's most capable Opus-tier model for complex reasoning and agentic coding.
Adaptive thinking
Always on — the only thinking mode on Claude Fable 5; depth tuned with the effort parameter up to max.
Adaptive thinking supported but optional; runs without thinking when unset.
Refusals and fallback
Safety classifiers return structured refusals; a fallback mechanism retries on another Claude model automatically.
Standard request handling without the classifier-based refusal and fallback flow.
Refusal billing
Requests refused before any output is generated are not billed; fallback credit offsets the prompt-cache cost of switching.
Standard billing on all completed requests.
Pricing tier
Premium per-token rates reflecting the top capability tier — see the live pricing card above.
Lower per-token rates on the Opus tier.
Context, output & vision
1M-token context, 128K max output, text + image input.
1M-token context, 128K max output, text + image input — at parity.
Comparison reflects publicly documented behavior from Anthropic's Claude Fable 5 launch documentation and model overview at the time of writing. Model behavior and pricing can change; check the pricing card above and the API docs for current values.
Ship Claude Fable 5 in three steps
- step 01
Create an account and key on api.reapi.ai
Sign up at api.reapi.ai, open the console, generate an API key under API Keys, and top up tokens under Top Up. The chat workspace is separate from the reapi.ai image/video gateway — keys do not cross over.
Open - step 02
Send your first Claude Fable 5 request
POST https://api.reapi.ai/v1/chat/completions with `model: "claude-fable-5"`, your `messages` array, and `max_tokens` set generously. The endpoint uses the standard chat-completions format, including streamed responses; the native Anthropic /v1/messages format works too. Claude Fable 5 takes no sampling parameters — leave `temperature` and `top_p` out of the request.
Open - step 03
Tune for cost and stability
Use prompt caching for stable system prompts and recurring long inputs to bring repeated-context costs down. Reserve Claude Fable 5 for the highest-value calls and route everything else to a cheaper model on the same key.
Open
Frequently asked questions
Common questions about this model.
Claude Fable 5 is billed pay-as-you-go in USD against your api.reapi.ai token balance — see the pricing card on this page for the live per-1M-token input and output rates. The full 1M context window is billed at standard rates with no long-context premium, and requests Claude Fable 5 refuses before generating output are not billed.
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