Anthropic Claude: Claude Opus 5.5 API
Claude Opus 5.5 is Anthropic's recommended starting point for most workloads, built for long-running agentic coding and knowledge work. It costs less than Claude Opus 5 while keeping the 1M-token context window and 128K output, with thinking always on and depth set by the effort parameter, which defaults to medium.
- Context window: 1,000,000 tokens
- Max output: 128,000 tokens
- Input: text, image, file
- Output: text
- Reasoning: Supported
- Tool calling: Supported
- File input: Supported
- Released: 2026-09-22
- Knowledge cutoff: 2026-06-30
Frequently Asked Questions
What is the context window of Claude Opus 5.5?
Claude Opus 5.5 supports a context window of up to 1,000,000 tokens.
Does Claude Opus 5.5 support function calling?
Yes. Claude Opus 5.5 supports tool / function calling.
Does Claude Opus 5.5 support reasoning?
Yes. Claude Opus 5.5 is a reasoning-capable model.
What is the knowledge cutoff of Claude Opus 5.5?
The knowledge cutoff of Claude Opus 5.5 is 2026-06-30.