Anthropic Python SDK v0.90.0 Adds Claude Mythos Preview Support

Anthropologic released version 0.90.0 of its Python SDK on April 7, 2026, introducing support for the claude-mythos-preview model and addressing a client-side bug.

What's New

Claude Mythos Preview Integration

The primary feature addition enables developers to call the claude-mythos-preview model through the Python SDK. This represents the first SDK-level support for the Mythos model variant, which Anthropic has not yet formally announced with full specifications or pricing.

Bug Fix

The update resolves an issue where hardcoded query parameters were not properly merged with user-provided parameters in the client. This fix ensures that internal SDK query parameters and custom user parameters can coexist without conflicts.

Technical Details

The release is a minor version bump (0.90.0 from 0.89.0), indicating backward compatibility. The change commits (fc7ddd8 and 32d35e0) are now available in the public repository.

What This Means

Developers using Anthropic's Python SDK can now integrate claude-mythos-preview into their applications, though details about the model's capabilities, context window, pricing, and performance benchmarks remain unavailable. The query parameter fix addresses a potential integration issue for users who rely on both SDK defaults and custom configurations. This SDK update typically precedes or accompanies formal model announcements, suggesting Mythos may receive broader availability soon.