The week of November 18, 2026, turned into one of the wildest weeks in the AI world. In just seven days, the title of “best AI model” changed three times. First, Google launched Gemini 3 Pro. A day later, OpenAI surprised everyone with GPT-5.1 Codex Max. And then, on November 24, Anthropic released Claude Opus 4.5, calling it the new top model especially for coding, agents, and computer-based tasks.
Inside Claude Opus 4.5
Anthropic never reveals much about its model architecture, but the system card gives a few insights. Opus 4.5 is a “hybrid reasoning” model, meaning it can give quick answers or switch into deep thinking mode when needed.
Just like Sonnet 3.7, it has two internal modes:
- Default Mode → fast, direct replies
- Extended Thinking Mode → more detailed reasoning for tough problems
The biggest upgrade is a new “effort” setting.
Users can pick Low, Medium, or High effort.
- Low = fast and cheap
- Medium = balanced
- High = maximum intelligence, no matter how many tokens it uses
The model was trained on data until May 2026.
It supports a 200,000-token context window and a 64,000-token output limit, similar to Sonnet 4.5.
This may feel small because Google already offers 1 million tokens.
Claude Opus 4.5 Performance & Benchmarks
Claude Opus 4.5 performs extremely well in technical work.
On the well-known SWE-bench Verified test (used to measure real coding ability), Opus 4.5 scored 80.9% on High effort—higher than both GPT-5.1 and Gemini 3 Pro.
Anthropic also tested the model with their in-house technical exam. Opus 4.5 scored better than every human who took that test.
Of course, comparing humans and AI on the same test can be misleading, but the performance still shows progress.
Another interesting behavior appeared in the τ2-bench test.
The model acted as an airline customer service agent.
A customer wanted to change a basic economy ticket—something normally not allowed.
Instead of rejecting the request, Opus 4.5 cleverly upgraded the ticket first and then changed the flight.
The benchmark marked this as “wrong,” but in real life, this kind of creative workaround could be useful for automated agents.
Even then, developers say the differences between new frontier models are becoming harder to notice in daily tasks. Some even say they can switch back to older models without losing productivity.
One area where Opus 4.5 clearly improves is efficiency.
Anthropic claims that at Medium effort, Opus 4.5 matches Sonnet 4.5’s score but uses 76% fewer output tokens.
This is a big advantage for companies running AI agents for long hours.
Claude Opus 4.5 Safety, Security & Prompt Injection
Anthropic says Opus 4.5 is harder to trick than other models.
Still, no model is fully safe.
A single prompt injection attempt succeeds about 4.7% of the time.
But if someone tries ten different attacks, the success rate jumps to 33.6%.
This is better than Gemini 3 Pro, which fails over 60% of the time.
Claude Opus 4.5 Availability, Tools & Pricing
Claude Opus 4.5 is now available through:
Anthropic API
AWS Bedrock
Google Vertex AI
Anthropic also released new updates:
- Plan Mode → creates a step-by-step plan before executing code
- Zoom Tool → lets the model inspect specific parts of a screen
The good news for developers is pricing.
Opus 4.5 is cheaper than the previous version:
- $5 per million input tokens
- $25 per million output tokens
It’s still not cheaper than GPT-5.1 or Gemini 3 Pro, but the price drop makes it suitable for everyday use, not just premium tasks.
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