About Claude Fable 5.1
Claude Fable 5.1 succeeds Claude Fable 5 as the generally available face of Anthropic's Mythos-class tier, sharing its underlying model with the invitation-only Claude Mythos 5.1 that Anthropic offers through Project Glasswing. Anthropic's own guidance is to start most workloads on Claude Opus 5 and reach for Claude Fable 5.1 when demanding reasoning or long-horizon agentic work needs more; it names long-running coding sessions, multistep research, and document, spreadsheet and slide work as the areas that moved furthest past its predecessor.
Adaptive thinking is always on, steered by an effort setting that defaults high; it reads text and images, writes text, and keeps the tier's million-token context window and large output allowance. Two details matter to integrators moving from earlier Claude models: forced tool choice is not supported, and its thinking blocks are bound to the model that produced them.
Input and output rates are unchanged from Claude Fable 5, so the headline cost of the tier holds; what moved is the cache-read price, which Anthropic cut to a quarter of what other Claude models charge relative to input — the callout above carries the multiplier. Anthropic's own estimate is that typical token-billed workloads come out meaningfully cheaper than on Claude Fable 5 as a result, with the largest savings on highly agentic sessions that re-read long prefixes every turn. Batch processing still halves standard rates, always-on thinking bills as output, and the tokenizer produces roughly a third more tokens than Claude models older than Claude Opus 4.7 did for the same text, so compare per-request costs rather than per-token rates across generations.
Frequently asked questions
How much does the Claude Fable 5.1 API cost?
Claude Fable 5.1 costs $10 per million input tokens and $50 per million output tokens, with cached input at $0.25 per million (98% off). Note: Cache reads are 2.5% of the input rate on this model (10% on other Claude models). Same input/output rates as Claude Fable 5.
How much does a typical chat message cost with Claude Fable 5.1?
A short chat message (about 500 input and 250 output tokens) costs roughly $0.018 with Claude Fable 5.1. At 1,000 such requests a day, that is about $525.00 per month.
Is Claude Fable 5.1 cheap compared to similar models?
Claude Fable 5.1 has the #28 cheapest input rate of the 29 models we track. On a mixed workload (10K input / 2K output), it costs $0.200 per request, versus $0.045 for GPT-4o.
What does Claude Fable 5.1 cost per 1,000 tokens?
Per 1,000 tokens, Claude Fable 5.1 costs $0.0100 for input and $0.0500 for output, or $0.00025 for cached input. Providers quote rates per million tokens ($10/M in, $50/M out here), so divide by a thousand for the per-1K figure older pricing pages used.
How large a prompt can Claude Fable 5.1 take?
Claude Fable 5.1 accepts up to 977K tokens of input context and can generate up to 125K tokens of output per request. At its input rate, filling the entire 977K-token window costs about $10.00 per request before any output.
Related
Compare all models at once ·Count tokens in your prompt
All Anthropic model costs: Claude Fable 5 · Claude Opus 5 · Claude Sonnet 5 · Claude Haiku 4.5 · Claude Opus 4.8
Last updated 2026-09-03. Prices verified against Anthropic's official pricing page; see the methodology.