Claude Opus 5.5 vs Sonnet 5.5
Specs and prices below are quoted from official vendor documentation (Anthropic, OpenAI), checked on 2026-10-16. Prices are the vendors’ list prices, not byesu’s; on byesu you are billed per token and see the actual price in the model list after you sign in.
At a Glance
| Item | Claude Opus 5.5 | Claude Sonnet 5.5 |
|---|---|---|
| Vendor | Anthropic | Anthropic |
| Official positioning | Long-running agentic coding and knowledge work; Anthropic’s recommended starting point | “The best combination of speed and intelligence” |
| Model ID on byesu | claude-opus-5-5 | claude-sonnet-5-5 |
| Context window | 1M | 1M |
| Max output | 128K | 128K |
| Knowledge cutoff | Jun 2026 | Jun 2026 |
| Reasoning control | Adaptive thinking, always on; default effort medium | Adaptive thinking; default effort high |
| Official list price (input / output per 1M tokens) | $4 / $20 | $2 / $10 |
| Official cached-input price (per 1M) | $0.20 | $0.10 |
| Official cost of 1M input + 200K output | $8 | $4 |
Key Differences
- Price: Opus 5.5 costs twice as much per token at list price ($4/$20 vs $2/$10). Cache reads are 5% of the input price on both.
- Speed: Anthropic rates Sonnet 5.5 “Fast” and Opus 5.5 “Moderate” in comparative latency.
- Thinking: both use adaptive thinking. Opus 5.5 always thinks and defaults to
mediumeffort; Sonnet 5.5 defaults tohigheffort. - Limits: identical — 1M-token context window, 128K max output, reliable knowledge through June 2026.
Which One Should You Pick?
- Long-running agents and hard, multi-step coding: Opus 5.5, which Anthropic positions for exactly this and recommends as the default starting point.
- Interactive chat, high-volume or latency-sensitive work: Sonnet 5.5 — faster, and half the list price.
- Mixed workloads: use Sonnet 5.5 by default and switch to Opus 5.5 for the tasks where its answers are measurably better.
Use Both With One Key
Both models are on byesu with the default auto-group token. To compare them on your own workload, keep the base URL and token and change only the model ID:
from openai import OpenAI
client = OpenAI(api_key="sk-YOUR_TOKEN", base_url="https://byesu.com/v1")
for model in ["claude-opus-5-5", "claude-sonnet-5-5"]:
resp = client.chat.completions.create(
model=model,
messages=[{"role": "user", "content": "Summarize this repository’s architecture"}],
)
print(model, resp.usage, resp.choices[0].message.content[:200])FAQ
How much more expensive is Opus 5.5 than Sonnet 5.5?
At list price, twice as much per token: $4 vs $2 per million input tokens and $20 vs $10 per million output tokens. Cache reads cost 5% of the input price on both.
Do Opus 5.5 and Sonnet 5.5 have the same context window?
Yes. Both have a 1M-token context window and up to 128K output tokens per request.
Which one should Claude Code use?
Both work. Set ANTHROPIC_MODEL to claude-opus-5-5 for long agentic sessions or claude-sonnet-5-5 for faster, cheaper turns; the base URL and token stay the same on byesu.