What is Claude Fable 5.1?
Claude Fable 5.1 is Anthropic’s model for demanding reasoning and long-horizon agentic work. Anthropic released it on September 1, 2026 and lists it as Active (latest) on its model page, alongside a 1M-token context window, a 128K-token maximum output and an input format of text and images. Anthropic’s own guidance is to start most workloads on Claude Opus 5, and to reach for Claude Fable 5.1 when evaluations on Opus 5 at a higher effort level still fall short. Here you meet it through an ordinary chat box: describe the task, attach an image, read a streaming answer and refine it in follow-up turns. The workspace does not expose every control Anthropic’s API offers, so the sections below keep the official specifications and this site’s controls apart.
What Claude Fable 5.1 is worth using for
Run a long task in checkpoints
Long-horizon work tends to go wrong in the middle, where nobody is reviewing. Ask for a plan, a file list and explicit checkpoints before any change, then approve one step at a time. Replies stream, so you can stop early when the direction is wrong.
Plan this refactor before you change anything. List the files you expect to touch, the order you would work in, and the checkpoints where you will stop and report progress. Wait for my confirmation before each step.
Turn notes and PDFs into decisions
Paste the text, or attach a PDF and let this site extract its text first. Ask for decisions, action items and open questions with the original sentence behind each one. Scans and complex layouts extract poorly, so paste the passage directly when the file matters.
I will paste the meeting notes below. Turn them into decisions, action items with owners, and open questions. Quote the sentence behind each decision, and mark anything the notes leave unspecified instead of filling it in yourself.
Work through a dense screenshot or chart
Claude Fable 5.1 takes text and images as input, so an interface screenshot or a dashboard is fair game. Say what you want read out of it, and ask for what is visible to be kept apart from what is inferred. Anthropic notes that the strongest chart reading comes with cropping tools; this workspace only offers the upload, so have unreadable labels flagged rather than guessed.
Here is a screenshot of a dense dashboard. Describe its information hierarchy and navigation, and tell me which labels are too small for you to read reliably. Keep what you can see separate from what you are inferring.
Check whether this model fits the job
Fable 5.1 sits at the long-running end of Anthropic’s lineup and is priced accordingly, so it is worth asking whether a task justifies it. Give the model the shape of the work — how long it runs, whether it needs outside tools, what a wrong answer would cost — and let it argue both sides before you commit.
Help me judge whether this task suits a long-horizon reasoning model. Ask me how long the work will run, whether it needs external tools, and how costly a wrong answer would be. Then argue for and against using the most capable model and give me your recommendation.
Official Claude Fable 5.1 specifications
- Developer
- Anthropic
- Model ID
- claude-fable-5-1
- Official context window
- 1M tokens
- Official maximum output
- 128K tokens
- Official input and output
- Text and images in, text out
- Reliable knowledge cutoff
- June 2026
Claude Fable 5.1 and Claude Sonnet 5 side by side
Every value below comes from the same comparison table on Anthropic’s Claude Fable 5.1 model page, checked on September 19, 2026. They describe the two API models rather than this website, and the prices are Anthropic list prices in US dollars, not what this site charges in points.
| Specification | Claude Fable 5.1 | Claude Sonnet 5 |
|---|---|---|
| Context window | 1M tokens | 1M tokens |
| Max output | 128K tokens | 128K tokens |
| Price per MTok, in / out | $10 / $50 | $2 / $10 |
| Comparative latency | Slower | Fast |
| Thinking | Adaptive (always on) | Adaptive |
| Default effort | high | high |
| Knowledge cutoff | Jun 2026 | Jan 2026 |
How to use Claude Fable 5.1 online
Choose the model
This page opens with Claude Fable 5.1 selected. The model navigation on the left and the selector in the chat box stay in sync, and switching models keeps the current conversation. Start a new chat when you want a clean context.
Describe the task and the output
State the goal, the constraints and the format you want back. Send one of the prompts from this guide as it is, or edit it first; for agentic work, more specific instructions tend to produce more usable answers.
Sign in, send and check the cost
Sending a message needs an account with available points. The composer reads a reference price from the live model catalog, and a finished request reports what it actually cost. Follow up with corrections rather than starting over.
What Claude Fable 5.1 costs
Anthropic lists Claude Fable 5.1 at $10 per million input tokens and $50 per million output tokens, with cache writes at $12.50 per million for the five-minute window and $20 per million for the one-hour window. Cache reads cost $0.25 per million, which is 2.5% of the input price, a lower multiplier than Anthropic applies to its other models. Batch requests are half price, and the full 1M-token context window is billed at the standard rate, so a 900k-token request costs the same per token as a 9k-token one. None of that is this site’s checkout price. Here you pay in points: the composer shows a reference price taken from the live catalog, and a finished request reports its actual cost. As of the information-check date below, that catalog entry lists input and output reference prices in a 1 to 5 ratio and a cache-read row at 2.5% of input — the same shape as Anthropic’s list prices, expressed in this site’s own unit.
View points and plans ↗Claude Fable 5.1 FAQ
Can I use Claude Fable 5.1 for free?
Browsing this page and preparing a prompt costs nothing. Sending a message needs an account with available points, so Claude Fable 5.1 is not an unlimited free service here. Whether an account has trial points depends on the offer shown inside that account; unlimited free chat is not promised.
Do I need an Anthropic API key?
No. This page runs on your NanoBanana Pro account and point balance. If you want to call Anthropic directly, the official model page and pricing page linked below are the right starting points.
Can it read images and PDFs?
Anthropic lists text and images as the inputs for this model. This site accepts JPEG, PNG, WebP and PDF files up to 24 MB, but a PDF is not sent as a document: the text is extracted first, so a scanned page or a complex layout may come back as an error. Paste the passage manually in that case. Audio and video uploads are not available.
Why are thinking and web search disabled?
Anthropic’s API exposes adaptive thinking with an effort parameter, and tool use that includes web search. The catalog entry this page runs on declares neither a reasoning level nor a search tool, so the composer disables both switches for Claude Fable 5.1 instead of pretending to offer them. A greyed-out control in the chat box means unavailable, not broken.
How long can an answer be?
Anthropic documents a 1M-token context window and a 128K-token maximum output for the API model. This site requests at most 4,096 output tokens per reply, which is a workspace setting rather than a model limit. Split long deliverables into parts; a task that needs the whole context window is better run against the API directly.
What happens when I switch models mid-conversation?
The left navigation and the chat selector update together, existing messages stay in the conversation, and the next request uses the newly selected model. A reply that is already streaming keeps the model that started it. Anthropic notes that thinking blocks can move onto Claude Fable 5.1 but not back off it; this workspace does not surface thinking blocks in either direction.
Can Claude Fable 5.1 generate images?
No. It takes text and images as input and returns text. You can ask it to describe an image or write a prompt for one, then generate the picture with an image model from the model library.
Is NanoBanana Pro the official Anthropic website?
No. NanoBanana Pro is an independent platform offering a shared workspace for several AI models. Anthropic develops Claude; the specifications and prices quoted on this page come from the official pages linked below.
Sources and model information
Information checked
Start with the task that keeps stalling
Give it the goal, the constraints and the format you need, then work through the job one checkpoint at a time.
Chat with Claude Fable 5.1 ↑