Claude Opus 5.5 vs Claude Fable 5.1
Same company, same 1M context, same June 2026 knowledge cutoff. The difference is price: Opus 5.5 lists at 40% of Fable 5.1 per token, and Anthropic itself says to start with Opus 5.5 for most workloads. Claude Fable 5.1 vs Claude Opus 5.5 in one table: list price, context window, output limit, cutoff and release date, with a cost calculator for your own monthly volume.
| Spec | Claude Opus 5.5 | Claude Fable 5.1 |
|---|---|---|
| Provider | Anthropic | Anthropic |
| Released | 2026-09-22 | 2026-09-01 |
| Input / 1M tokens | $4.00 | $10.00 |
| Output / 1M tokens | $20.00 | $50.00 |
| Cached input / 1M | $0.200 | $0.250 |
| Batch input / output | $2.00 / $10.00 | $5.00 / $25.00 |
| Context window | 1M | 1M |
| Max output | 128K | 128K |
| Knowledge cutoff | 2026-06 | 2026-06 |
| Image input | yes | yes |
| API ID | claude-opus-5-5 | claude-fable-5-1 |
| Status | Generally available | Generally available |
Cost at your volume
list price, per monthPaste your usage instead of typing
Paste a line from a provider invoice, a usage dashboard, or an API response. We look for input and output token counts (JSON keys like input_tokens, prompt_tokens, completion_tokens, or text like "1.2M in, 300k out"). Nothing leaves your browser.
Examples that work: {"usage":{"input_tokens":1200000,"output_tokens":300000}} · 1.2M in, 300k out · GPT-6.1 Sol: 2.4B input tokens, 310M output tokens
Same token counts on both sides. Real bills differ: tokenizers differ, reasoning models bill thinking tokens as output, and caching or batch discounts apply differently. Rank all models →
Pick Opus 5.5 if…
- Cost matters most: $24.00 vs $60.00 per 1M in + 1M out, 60% less.
- Your workload is cache-heavy: cached input is $0.200 vs $0.250 per 1M.
- Same provider: switching is a one-line model ID change (
claude-opus-5-5). - Anthropic says it performs at the level of Claude Fable 5.1 on most work and costs 40% less to run than Opus 5 at default settings.
Pick Fable 5.1 if…
- You have evals showing it beats Opus 5.5 on your task by more than the 60% price gap.
- Same provider: switching is a one-line model ID change (
claude-fable-5-1). - Stronger long-running agentic coding, multistep research, and document, spreadsheet and slide work than Fable 5 (vendor claim).
Price difference, in words
Per million tokens, Claude Opus 5.5 lists at $4.00 in / $20.00 out, against $10.00 / $50.00 for Claude Fable 5.1. That is 2.5× on input and 2.5× on output, or 60% less for a job that uses one million tokens each way ($24.00 vs $60.00).
With prompt caching, the gap moves: cached input is $0.200 on Opus 5.5 and $0.250 on Fable 5.1. Agent loops that re-send a large system prompt every turn pay mostly cached-input rates.
Benchmarks both vendors published
Only rows where both models have a number from a cited source. Vendor-reported; settings may differ between sources.
| Benchmark | Opus 5.5 | Fable 5.1 |
|---|---|---|
| Terminal-Bench 4.0 | 66.4% | 55.8% |
| GDPval-AA v2.1 (Elo) | 1846 | 1735 |
| OSWorld 2.1 (partial) | 81.8% | 80.7% |
- Claude Opus 5.5 model page (platform.claude.com) read 2026-10-08
release date, model IDs, context, output, pricing, cutoff - Anthropic pricing page read 2026-10-08
cache, batch, fast mode prices - Anthropic announcement: Claude Opus 5.5 read 2026-10-08
benchmarks (vendor-reported), availability, claims vs Opus 5
- Claude Fable 5.1 model page (platform.claude.com) read 2026-10-08
release date, model IDs, context, output, pricing, cutoff, positioning - Anthropic pricing page read 2026-10-08
cache, batch prices - Anthropic announcement: Claude Opus 5.5 (includes Fable 5.1 scores) read 2026-10-08
benchmarks (vendor-reported)