Sim is the open-source AI workspace where teams build, deploy, and manage AI agents. This page compares Claude Fable 5.1 and Claude Opus 5.5 on API pricing per 1M tokens, context window, max output, and capabilities. Both models are available in the Sim Agent block, and each Agent block in a Sim agent can use a different model.
API model comparison
Claude Fable 5.1 vs Claude Opus 5.5
Claude Opus 5.5 is 2.5× cheaper than Claude Fable 5.1: 1,000 agent calls with 10k input and 1k output tokens each cost $60 versus $150 at standard rates.
Claude Fable 5.1 charges $10 input and $50 output per 1M tokens; Claude Opus 5.5 charges $4 and $20.
Both models have a 1M token context window.
Both can generate up to 128k output tokens per response.
Both support configurable reasoning, tool choice control, and native structured outputs in Sim.
Pricing, context window, and capabilities
API prices are per 1M tokens. Pricing last updated .
| Metric | Claude Fable 5.1 | Claude Opus 5.5 |
|---|---|---|
| Provider | Anthropic | Anthropic |
| Input price | $10/1M | $4/1M |
| Cached input | $0.25/1M | $0.2/1M |
| Output price | $50/1M | $20/1M |
| Context window | 1M tokens | 1M tokens |
| Released | Sep 1, 2026 | Sep 22, 2026 |
| Temperature | Not configurable | Not configurable |
| Reasoning effort | Not supported | Not supported |
| Verbosity | Not supported | Not supported |
| Thinking levels | low, medium, high, xhigh, max (default: high) | low, medium, high, xhigh, max (default: medium) |
| Structured outputs | Supported (native) | Supported (native) |
| Tool choice | Supported | Supported |
| Computer use | Not supported | Not supported |
| Deep research | Not supported | Not supported |
| Memory support | Supported | Supported |
| Max output tokens | 128k | 128k |
Use Claude Fable 5.1 or Claude Opus 5.5 in a Sim agent
Both models are available in the Sim Agent block. Pick either one from the model picker, and each Agent block in the same agent can use a different model.
Frequently asked questions
Claude Opus 5.5 is 2.5× cheaper than Claude Fable 5.1: 1,000 agent calls with 10k input and 1k output tokens each cost $60 versus $150 at standard rates. Claude Fable 5.1 charges $10 input and $50 output per 1M tokens; Claude Opus 5.5 charges $4 and $20.
