Claude Mythos 5 Leaked — Anthropic Is Building a 4th Model Class Beyond Opus

A new Claude model slug has been spotted via Dev Mode: Claude Mythos 5. Not Haiku. Not Sonnet. Not Opus. A fourth model class entirely — planned as its own family alongside the existing three tiers.

What a 4th Model Class Means

Anthropic’s current lineup serves three market segments: Haiku (fast, cheap, lightweight tasks), Sonnet (balanced, most popular), and Opus (maximum capability, premium price). Three tiers, three price points, three use cases.

Mythos as a fourth class signals one of two strategies:

Above Opus — a frontier push. A “super-premium” tier for the hardest tasks: multi-hour autonomous research, complex multi-step reasoning, full codebase generation. Pricing likely $100-200 per million tokens. Targets enterprises with the highest-value workflows where cost-per-token is irrelevant compared to the value of the output.

Between tiers — a segmentation play. Filling the gap between Sonnet’s mass-market appeal and Opus’s premium positioning. This would directly pressure OpenAI’s GPT-5 pricing in the mid-premium segment — forcing a price war where Anthropic has the architectural advantage.

The IPO Context

Anthropic filed its S-1 at a $965 billion valuation. A fourth model class expands the addressable market at precisely the moment Anthropic needs to demonstrate to public market investors that its revenue can grow across multiple segments simultaneously — not just the Claude Sonnet middle.

The model layer is segmenting faster than three tiers can serve. Mythos is Anthropic’s answer — and the naming choice (mythology, not music) suggests this isn’t an incremental addition. It’s a new category.

Sources

• @testingcatalog — Claude Mythos 5 model slug spotted via Dev Mode

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