Technical specifications of Claude Opus 5.5
| Item | Claude Opus 5.5 |
|---|---|
| Provider | Anthropic |
| Model ID | claude-opus-5-5 |
| Input → output | Text and images → text |
| Context window | 1M tokens |
| Max output | 128K tokens |
| Batch API max output | 300K tokens (beta header) |
| Thinking | Adaptive, always on |
| Default effort | medium |
| Knowledge cutoff | June 2026 |
| Training data cutoff | June 2026 |
| Release date | September 22, 2026 |
| Status | Active, latest |
| Primary focus | Long-running agentic coding and knowledge work |
These specifications come from Anthropic's current model documentation.
What is Claude Opus 5.5?
Claude Opus 5.5 is an Opus-family model optimized for sustained agentic software engineering and knowledge-work workflows. Anthropic positions it for long-running jobs such as codebase-wide migrations, audits, tool-driven development, and complex professional work, while retaining text-and-image input, vision, multilingual capabilities, and tool use.
Main features of Claude Opus 5.5
- 1M-token context: The model supports a million-token context window, allowing long repositories, extensive documentation, and multi-stage task histories to remain in context.
- Always-on adaptive thinking: Thinking cannot be disabled; the
effortsetting controls thinking depth, latency, and cost, withmediumas the default effort. - Agentic coding: Anthropic specifically targets long-running coding, codebase migrations, audits, and multi-step engineering workflows.
- Vision and visual reasoning: The model accepts image input and Anthropic reports sharper reading of charts, diagrams, and screenshots without requiring the visual workarounds used for earlier models.
- Broad tool support: Claude Opus 5.5 supports server-side and client-side tools, Files API, PDF support, vision, prompt caching, batch processing, task budgets, and computer use through the newer
computer_toolset_20260801on the Claude API and Google Cloud. - Long-running conversation controls: Preserved thinking and conversation-bound thinking blocks are supported, while compact-on-demand is available as a beta feature for supported workflows.
Benchmark performance of Claude Opus 5.5
Anthropic-reported benchmark figures published around the launch include the following results, as reproduced by independent coverage of the announcement:
| Benchmark | Claude Opus 5.5 | Comparison context |
|---|---|---|
| Terminal-Bench 4.0 | 66.4% | Fable 5.1: 55.8%; Opus 5: 52.3%; GPT-6 Astra: 57.9% |
| FrontierCode v1.1 (Main) | 54.4% | Fable 5.1: 50.3%; Opus 5: 48.0%; GPT-6 Astra: 53.3% |
| CursorBench 4.0 | 57.8% | Fable 5.1: 51.8%; Opus 5: 46.6% |
| GDPval-AA v2.1 | 1,846 | Fable 5.1: 1,735; Opus 5: 1,708; GPT-6 Astra: 1,542 |
| Humanity's Last Exam | 67.7% with tools | Fable 5.1: 65.6%; Opus 5: 63.6%; GPT-6 Astra: 57.2% |
| OSWorld 2.0 | 81.8% partial | Fable 5.1: 80.7%; Opus 5: 74.0% |
| Chartography | 89.0% with tools | Fable 5.1: 88.4%; Opus 5: 83.4% |
Benchmark values should be read in the context of each benchmark's harness, tool configuration, and evaluation protocol rather than as a universal measure of model quality.
Claude Opus 5.5 vs claude Fable 5.1 vs Claude Sonnet 5
| Model | Context | Max output | Default effort | Primary positioning |
|---|---|---|---|---|
| Claude Opus 5.5 | 1M | 128K | medium | Long-running agentic coding and knowledge work |
| Claude Fable 5.1 | 1M | 128K | high | Demanding reasoning and long-horizon agentic work |
| Claude Sonnet 5 | 1M | 128K | high | Speed/intelligence balance |
The choice between these models depends on the workload. Anthropic's model overview describes Opus 5.5 as the general starting point for most workloads, Fable 5.1 for demanding reasoning and long-horizon agentic work when Opus 5.5 at higher effort falls short, and Sonnet 5 for a faster speed/intelligence balance.
How to Access Claude Opus 5.5 API with CometAPI
CometAPI provides a unified API layer for accessing AI models without requiring developers to build a separate provider integration for every model. For a Claude Opus 5.5 integration, developers can select the claude-opus-5-5 model through the CometAPI environment and use the platform's API credentials and endpoint configuration.
A typical workflow is:
- Create or access a CometAPI account and obtain an API key.
- Select
claude-opus-5-5as the target model in the CometAPI model/API interface. - Send the request and process the response through the CometAPI-compatible API layer.
This approach is useful for applications that need to switch between Claude models or compare Claude with other LLM providers without maintaining separate authentication and billing integrations for every provider.