Anthropic released its Opus 5 AI model on Friday, claiming that it "comes close to the frontier intelligence of Claude Fable 5 at half the price." That's welcome news for enterprises beset by rising token costs.

Fable 5 prices tokens at $10 / MTok input and $50 / MTok output, while Opus 5 prices tokens at $5 / MTok and $25 / MTok. OpenAI's GPT-5.6 Sol sells for $5 / MTok input and $30 / MTok output.

However, the tokens required to complete a task can vary from model to model, so it's also useful to assess how much each model costs to complete the same task.

Per Artificial Analysis, the weighted average cost (USD) per Intelligence Index task is $2.75 for Fable, $2.03 for Opus 5 (max), $1.04 for GPT-5.6 Sol (max), and $0.95 for Kimi K3. 

Opus 5 leads the Artificial Analysis Intelligence Index at 61, one point ahead of Fable.

"Claude Opus 5 provides greatly improved performance for the same cost as its predecessor, Opus 4.8," Anthropic claims.

Opus 5 should offer customers more context to fill because Anthropic has put the model's system prompt on a diet. According to Claude Code engineer Thariq Shihipar, Anthropic removed 80 percent of the Claude Code system prompt for its latest models.

As a result, the company's guidance for crafting prompts, skills, and CLAUDE.md files has changed. 

"Across your system prompt, skills, and CLAUDE.md files, you may need to simplify just like we did," said Shihipar, adding that a command called `claude doctor` can help automatically optimize some prompts and skills.

Users of Opus 5 however may find the model's responses wordier – at their expense. Anthropic cautions, "Claude Opus 5's default user-facing responses run longer than prior Opus models'." Customers who don't want the new verbosity are advised, "To control response length, prompt for it explicitly."

Opus 5 scores close to Mythos on finding vulnerabilities in open source code (80 percent OSS-Fuzz benchmark score compared to 79.4 percent), but is significantly weaker in weaponizing those findings – it succeeded in 4/14 exploitation attempts compared to 13/14 for Mythos.

The model's system card states, "Claude Opus 5 is substantially stronger than Claude Opus 4.8 across the board, with the largest gains in agentic coding, computer use, and long-horizon knowledge work." It is said to be comparable to, or in some cases ahead of, Claude Fable 5 and Claude Mythos 5.

The model is likely to be significantly more useful for cybersecurity and biology tasks because it should refuse to cooperate less often. According to Anthropic, "Opus 5’s cyber classifiers are proportionally less restrictive than those on Fable 5. They allow Opus 5 to find vulnerabilities in source code, but block 'binary-based' vulnerability scanning (a method more likely to be associated with malicious actors), penetration testing, and exploit generation."

Anthropic is also making life easier for those frustrated by model refusals. It's rolling out an automated fallback function on its API so requests deemed too dangerous to entrust to Opus 5 or Fable 5 can be routed to a less capable model instead of being blocked outright.

Opus 5 is said to be Anthropic's "most aligned model to date," meaning it's the least likely to go off its guardrails.

A more compelling selling point for businesses is likely to be the lack of a data retention requirement. ®