The two most capable cybersecurity models in 2026 now have a clear scoreboard. On June 22, OpenAI released the full version of GPT-5.5-Cyber and pointed straight at Anthropic: its new model scores 85.6% on the CyberGym benchmark, ahead of Anthropic's Mythos 5 at 83.8% and OpenAI's own base GPT-5.5 at 81.8%. After a year of Anthropic setting the pace on AI-driven vulnerability discovery, OpenAI is claiming the top of the chart.

But a 1.8 point benchmark lead is not a buying decision. These models differ far more in how you get them, how they are governed, and what workflow they are built around than in raw score. One is a limited release to verified defenders; both wrap their most capable cyber behavior in safety-led access controls. Picking the right one means looking past the headline number.

This comparison breaks down the benchmark, the access and governance models, the patching workflow, the partner ecosystems, and a practical decision framework. For a deeper look at GPT-5.5-Cyber on its own, see our GPT-5.5-Cyber and Daybreak defender guide.

1GPT-5.5-Cyber vs Mythos 5 at a Glance

The one-line read: GPT-5.5-Cyber currently leads on the headline benchmark and ships with a more explicit end-to-end patching toolchain, while both vendors converge on the same core idea, which is that frontier cyber capability must be paired with strict access governance. The interesting decisions live in the rows below the score.

2The CyberGym Benchmark, Read Honestly

CyberGym tests whether an AI agent can reproduce known vulnerabilities in real-world software. The full ranking from the launch looks like this:

Three things are worth saying plainly. First, the cyber-specific tuning matters: GPT-5.5-Cyber beats its own base model by 3.8 points, which is the value of specialization rather than just scale. Second, the gap over Mythos 5 is 1.8 points, close enough that benchmark noise, harness differences, and task selection can move it. Treat it as "GPT-5.5-Cyber is at least competitive and currently ahead," not "GPT-5.5-Cyber wins by a mile."

For the general-purpose capabilities behind these cyber variants, including coding and reasoning benchmarks, our Claude Mythos vs GPT-5.5 benchmarks and pricing comparison goes deeper on the base models.

3Access & Governance: The Real Differentiator

This is where the two diverge in a way that actually affects your rollout. GPT-5.5-Cyber is delivered through OpenAI's Trusted Access for Cyber (TAC), the governance model underpinning Daybreak. It defines two tiers: GPT-5.5 with TAC for most defenders, covering secure code review, patching, threat modeling, and blue teaming, and GPT-5.5-Cyber itself for verified defenders protecting critical infrastructure, gated behind identity verification.

Anthropic took a parallel safety-led path with its Mythos line, constraining the most capable cyber behavior behind its own controls. Both vendors landed on the same principle independently: a model good enough to find and exploit vulnerabilities is dual-use, so more capability is paired with more verification.

If you need to bring this to a board or risk committee, our CISO board-readiness guide for AI cyber risk covers the governance questions both models raise.

4Discovery vs End-to-End Patching

The clearest product difference is workflow emphasis. Anthropic's Mythos line built its reputation on discovery, finding flaws faster than human researchers. OpenAI is leaning into the next step, arguing that finding bugs is no longer the bottleneck, shipping the fix is. Its Codex Security plugin was updated to cover the full pipeline: discover, validate, generate a patch, and prevent new vulnerabilities from reaching production.

Notably, both vendors now agree on this framing. The race has shifted from "who finds more" to "who closes the loop," and GPT-5.5-Cyber's end-to-end patching story is OpenAI's bet that the loop is where defenders feel the most pain.

If your pain is a backlog of unpatched findings rather than a shortage of findings, the end-to-end emphasis is the more useful framing. Our patch velocity guide explains why that backlog is the metric that actually moves risk.

5Ecosystem, Partners & Open Source

Beyond the model, each vendor is building a distribution and trust ecosystem. OpenAI's Daybreak Cyber Partner Program brings in 25+ security firms and several governments, letting vendors embed trusted access into their own products so you can reach GPT-5.5-Cyber capability without qualifying directly. On the open-source side, Patch the Planet, built with Trail of Bits, targets critical projects including cURL, NATS Server, pyca/cryptography, Sigstore, aiohttp, the Go project, freenginx, Python, and python.org.

Anthropic has run its own vendor partnerships and responsible- disclosure efforts around the Mythos line. The strategic difference is visibility: OpenAI has packaged its open-source contribution as a named, public program with a recognizable security partner, which is as much a trust-building move as a technical one.

For most buyers, the partner ecosystem matters more than the open- source program. If your existing security vendor is in the Daybreak partner network, that is often the smoothest path to this class of capability regardless of which model tops the benchmark this quarter.

6Pricing & Availability Reality

Be skeptical of any article that quotes a tidy per-token price for these cyber tiers. Neither GPT-5.5-Cyber nor the most capable Mythos cyber behavior is sold as a standard self-serve API product with public pricing. GPT-5.5-Cyber is a limited release to verified defenders, and the broadly available route is GPT-5.5 with Trusted Access. Anthropic similarly gates its top cyber capability.

The honest takeaway: both models are procurement decisions, not API signups. Treat them like enterprise security tooling and the comparison becomes about fit and trust, not a spreadsheet of token prices.

7Which One Should You Choose?

A short decision framework, since the benchmark gap is too small to decide on its own:

• Choose GPT-5.5-Cyber if you want the current CyberGym leader, you value the explicit discover-to-patch toolchain in Codex Security, or your security vendor is in the Daybreak partner network.
• Choose Claude Mythos 5 if you are already standardized on Anthropic and Claude Code, you weight its safety-first reputation heavily, or its discovery strengths map to your primary use case.
• Choose the broadly available tier first in almost all cases. GPT-5.5 with Trusted Access for Cyber, plus a disciplined human-review process, will deliver most of the value while you decide whether you genuinely need the most permissive model.
• Do not choose on benchmark alone. A 1.8 point CyberGym gap should not override ecosystem fit, existing contracts, or your team's familiarity with one vendor's tooling.

The teams that win with either model already have a vulnerability management process and are using AI to run it faster, not hoping the model invents one for them.

8Why Lushbinary for AI Security Integration

Whether you land on GPT-5.5-Cyber, Claude Mythos 5, or the broadly available tier of either, the value comes from the workflow you build around the model. Lushbinary helps engineering and security teams integrate AI-assisted vulnerability discovery and patch generation into real CI pipelines, with the scoping, logging, and human-review gates that keep the capability defensive and auditable.

We are model-agnostic. We will help you evaluate the access paths, stand up the integrations, and design guardrails that satisfy your compliance posture, so the decision between OpenAI and Anthropic becomes a detail rather than a blocker.

9Frequently Asked Questions

Sources

• OpenAI: Daybreak, securing every organization in the world
• The Decoder: GPT-5.5-Cyber outperforms Anthropic's Mythos on cyber benchmark
• Neowin: GPT-5.5-Cyber tops Claude Mythos 5 in vulnerability benchmark
• OpenAI Help Center: Trusted Access for Cyber overview

Content was rephrased for compliance with licensing restrictions. Benchmark figures and access terms sourced from official OpenAI announcements and reputable security reporting as of June 2026. Model capabilities and availability may change - always verify on the vendor's website.