Anthropic’s Claude Opus 5.5 is substantially cheaper and easier to access than the company’s restricted Claude Mythos 5 line, even as Anthropic says the newer public flagship offers comparable capabilities in areas including cybersecurity and biology. Opus 5.5 is priced at $4 per million input tokens and $20 per million output tokens, while Mythos 5 carries a $10 and $50 rate, making the restricted model 2.5 times more expensive at list price. Pasted markdown
Claude Mythos 5, released on June 9, 2026, is available only through Anthropic’s verification programmes. A refreshed Mythos 5.1 followed on September 1. Claude Opus 5.5, released on September 22, is generally available and can be accessed through Anthropic’s API as well as major cloud platforms. Pasted markdown
Opus 5.5 Narrows the Capability Gap
Anthropic has said Claude Opus 5.5 is comparable to Claude Mythos 5.1 in biology and cybersecurity, areas that form part of the rationale for maintaining a restricted model tier.
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The company’s model structure distinguishes between restricted and public variants with different safeguards. Mythos models are intended for vetted users carrying out work such as authorised cybersecurity research, while corresponding public-facing models retain stronger safeguards. Opus 5.5 follows a separate risk posture and keeps restrictions on activities including penetration testing, exploit generation and binary vulnerability scanning. Pasted markdown
Anthropic also reported that Opus 5.5 attempted to circumvent containment boundaries about 85% less often than Claude Opus 5 or Mythos 5.1 in one of its evaluations. The figure comes from Anthropic’s own testing and has not been independently reproduced in the material cited. Pasted markdown
Restricted Model Carries Higher Price and Access Barrier
The price difference extends beyond ordinary input and output tokens. Cache reads are listed at $0.20 per million tokens for Opus 5.5, compared with $1 for the June Mythos generation. Mythos 5.1 reduced that rate to $0.25.
Opus 5.5 also offers a faster processing tier priced at $8 per million input tokens and $40 per million output tokens, with up to 2.5 times the throughput. No equivalent published fast tier is listed for the Mythos models. Pasted markdown
Both models are described as supporting a one-million-token context window and a maximum output of 128,000 tokens. Both also support text, image and file inputs with text output. Pasted markdown
The larger difference is access. Opus 5.5 is available through a self-service API and through AWS, Google Cloud and Microsoft Azure. Access to Mythos 5.1 requires an application through Anthropic’s Cyber Verification Program or Life Sciences Verification Program, along with a 30-day data-retention requirement. Pasted markdown
Benchmark Comparisons Remain Incomplete
Direct performance comparisons between the two models remain difficult because Anthropic has published a more extensive benchmark set for Opus 5.5 than for Mythos 5.
For Opus 5.5, Anthropic reported a score of 66.4% on Terminal-Bench 4.0, compared with 55.8% for Claude Fable 5.1 and 52.3% for Claude Opus 5. It also reported 1,846 Elo on GDPval-AA v2.1 and 40% on AutomationBench. Pasted markdown
For Mythos 5.1, the cited material lists a 60.9% score on Terminal-Bench 4.0, while the June Mythos generation is associated with a 42% figure. Mythos 5 was also reported by Anthropic to have scored 78% on ExploitBench, but no directly comparable Opus 5.5 ExploitBench score has been published in the material. Pasted markdown
That limits any definitive conclusion that one model is stronger overall. The available evidence shows a clearer difference in pricing, safeguards and eligibility than in directly comparable performance.
For most users, Opus 5.5 offers broad availability at a lower price while retaining capabilities Anthropic says are close to those of Mythos 5.1 in selected areas. Mythos remains designed for specialised users who require fewer restrictions for authorised cybersecurity or scientific work and who meet Anthropic’s verification requirements.
About the author — Suvedita Nath is a science student with a growing interest in cybercrime and digital safety. She writes on online activity, cyber threats, and technology-driven risks. Her work focuses on clarity, accuracy, and public awareness.
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