Claude Opus 4.5

Overview. Claude Opus 4.5 is Anthropic's flagship proprietary model, released November 2025, built for complex coding, research, and long-document reasoning. It accepts text and image input and returns text, with a 200K-token context window and an optional extended thinking mode for deeper reasoning on demand. Developers reach for it when a task genuinely needs frontier-tier reasoning depth rather than a fast, lightweight response.

Key strengths. Opus 4.5 scores 0.87 on GPQA-diamond and 0.74 on MMMU-Pro, reflecting strong performance on graduate-level science reasoning and multimodal understanding. Its terminalbench_hard score of 0.47 demonstrates competence in sustained, multi-step agentic tool-use inside a terminal environment. Anthropic positions it as the deepest capability tier in the Claude Opus 4 family, and its Arena standing has historically placed it well above typical frontier cutoffs.

When to use it. Use Opus 4.5 for complex coding tasks, research synthesis, and reasoning over long documents where the 200K context window matters. Turn on extended thinking when a problem needs deliberate multi-step reasoning rather than a quick answer; leave it off for everyday interactive use through the API, Claude apps, or supported cloud platforms. It's a strong fit for agentic tool-calling workflows that require the model to track state across several steps.

Limitations. Context is capped at 200K tokens with a 64K-token maximum output, and the model's broader training data extends only to around May 2025. Extended thinking improves reasoning quality but shifts response behaviour away from fast, interactive latency toward slower, more deliberate output. The model is text-and-image in, text-only out — it does not accept or produce audio.

Sovereignty note. Anthropic is a US-based creator, and Inference on Opus 4.5 carries CLOUD Act exposure as a result. Anthropic's open-weights policy is mixed, and this model itself is closed-weight and proprietary — organisations with strict data-residency requirements should factor this into their routing decisions via the Smart Router.