OpenAI's coding assistant Codex has reached a major milestone with 3 million weekly users, leading CEO Sam Altman to reset usage limits for all users as a celebration. The announcement comes as Anthropic's rival Claude Mythos, a powerful new AI coding tool, has demonstrated the ability to discover thousands of security vulnerabilities across major software platforms. These competing developments highlight the intensifying race between OpenAI and Anthropic in the enterprise coding AI space .

What Is Codex and Why Does This Milestone Matter?

Codex is OpenAI's answer to Anthropic's Claude Code, designed to help developers write and debug software more efficiently. The tool has experienced explosive growth, gaining 1 million new users in less than a month, according to Codex head Thibault Sottiaux . To reward this rapid adoption, Sam Altman announced on X that OpenAI would reset usage limits for every 1 million new users Codex gains, with plans to continue this practice until the tool reaches 10 million weekly users.

"Three million people are now using Codex weekly, up from two million a little under a month ago. Incredible to see the growth," stated Thibault Sottiaux, Codex head at OpenAI.

Thibault Sottiaux, Codex Head at OpenAI

The limit reset is significant for users because it essentially gives them a clean slate. If a user had already consumed 20 percent of their monthly usage allowance, they can now start from zero and use the tool again without restrictions for the remainder of the billing period . This strategy appears designed to encourage continued adoption and reduce friction for power users.

How Does Claude Mythos Compare, and What Are the Security Implications?

While OpenAI celebrates Codex's user growth, Anthropic has unveiled Claude Mythos, a coding AI that represents a significant leap in capability, though with troubling implications. Claude Mythos can identify thousands of software vulnerabilities across major web browsers and operating systems that human security researchers missed . The tool is so powerful that it has prompted serious concerns about its potential misuse.

"Mythos is very powerful, and should feel terrifying," noted Boris Cherny, Claude Code creator at Anthropic.

Boris Cherny, Claude Code Creator at Anthropic

Anthropic is taking a cautious approach to Claude Mythos deployment. Rather than releasing it to the general public, the company is working with major technology firms like Google and Microsoft through an initiative called Project Glasswing to identify and fix security vulnerabilities before they can be exploited . This responsible disclosure model reflects the company's awareness of the risks posed by such a powerful tool.

How to Understand the Competitive Landscape Between OpenAI and Anthropic

• Revenue Growth: Anthropic's run-rate revenue has surged to $30 billion, up from $9 billion at the end of 2025, now exceeding OpenAI's estimated $25 billion as of March 2026 .
• User Adoption: OpenAI's Codex is growing rapidly with 3 million weekly users and gaining 1 million new users monthly, while Claude-based tools are also seeing strong adoption despite some rate-limiting issues .
• Valuation Gap: OpenAI remains valued at $852 billion compared to Anthropic's $380 billion valuation, though Anthropic's revenue trajectory is narrowing this gap .
• Product Strategy: OpenAI is doubling down on enterprise coding products with Codex, while Anthropic is positioning Claude Mythos as a security-focused tool for enterprise partnerships rather than public release .

The competitive dynamics reveal two different philosophies. OpenAI is pursuing aggressive user growth and public availability, while Anthropic is emphasizing controlled deployment and security-first development. OpenAI's decision to reset usage limits for Codex users every 1 million new users suggests the company is willing to absorb short-term revenue impact to drive adoption and market share in the coding AI space .

The timing of these announcements is notable. OpenAI is preparing for a public offering before the end of 2026, making user growth metrics particularly important for the company's valuation narrative. Anthropic's surging revenue and the capabilities demonstrated by Claude Mythos suggest that the company's enterprise-focused strategy is paying off financially, even without pursuing a public market listing .

For developers and enterprises evaluating coding AI tools, the choice increasingly comes down to accessibility versus capability. Codex offers broad availability and rapid iteration, while Claude Mythos represents cutting-edge vulnerability detection capabilities deployed through controlled partnerships. Both approaches reflect the broader tension in AI development between innovation speed and responsible deployment .