Nine UK Banks Blocked from AI Cybersecurity Tool as Tech Giants Battle for Financial Sector Access

A significant technology divide is emerging in the UK financial sector as nine major banks find themselves blocked from accessing Anthropic's Claude Mythos AI cybersecurity tool, according to a BBC Business report^[1]. OpenAI has swiftly moved to offer these institutions access to its rival GPT-5.5 Cyber tool, marking a new battleground in the race to provide advanced AI security solutions to financial institutions.

The development affects a sector that includes more than 111,000 companies classified as holding companies in the CompanyPulse company register^[2], with financial services firms facing critical decisions about their cybersecurity infrastructure as AI capabilities rapidly evolve.

The AI Tools at the Centre of the Storm

Both Claude Mythos and GPT-5.5 Cyber are designed to find hidden security weaknesses in digital systems and can outperform humans at some hacking and cyber-security tasks^[1]. Mythos caused particular concern when it was announced in April, with Anthropic claiming it had found a weakness in one legacy system which had remained hidden for nearly 30 years^[1].

The AI Security Institute, which has tested both tools, said in its report that they reached "a similar level of performance" in the tasks it set them^[1]. However, according to a company representative, Anthropic believes that Mythos' capabilities sit in a tier above 5.5 Cyber and therefore more caution is required^[1].

Banks Caught in the Crossfire

The UK banks which will now gain access to OpenAI's GPT 5.5 Cyber include Lloyds Banking Group, HSBC and Nationwide^[1]. NatWest and Santander already have access under existing agreements^[1]. This selective access creates a patchwork of capabilities across the UK banking sector, potentially affecting competitive positioning.

Bank of England governor Andrew Bailey warned last week that UK banks were still unable to access Mythos to test the security of their own digital systems and apps^[1]. Some finance ministers, central bankers and financiers have expressed serious concerns about Mythos, fearing the model could undermine the security of all financial systems^[1].

Strategic Implications for Financial Technology

The technology consultancy sector, which includes 166,990 active companies according to CompanyPulse data^[2], faces new opportunities as banks seek alternative solutions and advisory services in navigating this AI divide. Similarly, the 100,814 business and domestic software development companies^[2] may find increased demand for custom security solutions.

Former UK Chancellor George Osborne, now a senior executive at OpenAI, told the BBC that his firm did not want to "hide [5.5 Cyber] away or keep it to ourselves"^[1]. He emphasised: "The key things with these tools is that they need to be in the hands of the right people. We want to make sure that the forces that are establishing order in our democracies have these tools, and the forces that want to disrupt us or commit crime, do not."^[1]

Access Patterns and Commercial Considerations

Anthropic initially opened Mythos to a collective of 42 companies, mostly other US tech firms^[1]. The company is reportedly working urgently to expand access to Mythos^[1]. Meanwhile, OpenAI has been more generous with access to Cyber 5.5, opening it up in the EU and also to banks in Japan and Canada, among others^[1].

Both firms charge for usage, although Anthropic put $100m towards Mythos previews^[1]. This significant investment underscores the strategic importance both companies place on penetrating the financial services market.

Looking Forward: A Fragmented Landscape

The current situation creates a complex landscape for UK financial institutions. With different banks having access to different AI security tools, the sector faces potential disparities in cybersecurity capabilities. This fragmentation comes at a time when the UK has seen significant company formation activity, with 14,617 new incorporations in the past seven days alone according to CompanyPulse register statistics^[2].

As AI continues to transform cybersecurity practices, the selective availability of these tools may influence competitive dynamics within the UK banking sector. Financial institutions without access to either Mythos or GPT-5.5 Cyber may need to explore alternative solutions or wait for broader availability. The situation highlights the growing importance of strategic technology partnerships in maintaining competitive advantage in financial services.