Anthropic's Claude Opus 5.5 arrived on OpenRouter on 22 September 2026. On the Artificial Analysis Intelligence Index, read 23 September, it scores 58. The previous high in our catalog was 53, shared by Claude Fable 5.1 and GPT-6 Astra.
The price is the more surprising part. Opus 5.5 does not charge for that lead. It costs less than the model it replaces.
Against its own family and the flagship tier
Prices are the published list prices on each model author's own endpoint. Throughput and time to first token are OpenRouter's median (p50) over a trailing thirty-minute window on that endpoint. They are live marketplace telemetry for one route, not a CompareLLM measurement.
What changed from Opus 5
- Seven points on the index. Opus 5 scores 51 and Opus 5.5 scores 58.
- 20% cheaper on both sides. Input drops from $5 to $4 and output from $25 to $20. Cached input drops from $0.50 to $0.20.
- About 22% faster to stream. Median throughput is 72 tok/s against 59. Time to first token is slightly longer, 4.2 s against 3.7 s.
Context (1M tokens) and the output ceiling (128K) are unchanged. The endpoint accepts text, images and files, and it takes a reasoning_effort parameter, so effort is configurable per request.
Opus 5.5 against the $50 tier
This is the comparison that matters to anyone currently paying flagship prices. Fable 5.1 and GPT-6 Astra both list at $10 input and $50 output. Opus 5.5 is 2.5× cheaper on both and scores five points higher on the index. It also streams at 1.5× Fable's speed and 2× Astra's.
A composite index does not decide every workload. Our own category ratings for these models are still editorial estimates anchored to that index. They are labelled Estimated and carry no benchmark coverage until accepted results land. Treat the gap as a strong prior, not a verdict on your task.
Bottom line
If you use Opus 5 today, 5.5 is cheaper, faster and better on every figure we can source. If you pay $50 per million output tokens for Fable 5.1 or GPT-6 Astra, the published numbers make that premium hard to justify.
Every figure above carries its source and date on the model pages.
