Claude Sonnet 5 (Free) API
About
Build advanced reasoning agents with Claude Sonnet 5 (Free), a specialized AI model optimized for complex logic and chain-of-thought tasks. This model delivers available completely free of charge, native tool calling support. Access Claude Sonnet 5 (Free) via the ZenMux API with up to 128K output tokens.
Capabilities
Input Modalities
textimagepdf
Output Modalities
text
Reasoning
Yes
Structured Output
No
Tool Use
Yes
WeightsClosed
Temperature
Fixed
Attachment
Supported
Limits
Context Window
1.0M
Tokens
Input Limit
1.0M
Tokens
Max Output
128K
Tokens
Pricing
Standard (per 1M tokens)
Input
Free
Output
Free
Caching (per 1M tokens)
Read
Free
Write
Free
Frequently Asked Questions
Claude Sonnet 5 (Free) by ZenMux costs Free per 1M input tokens and Free per 1M output tokens. Cached reads cost Free per 1M tokens. Cache writes cost Free per 1M tokens.
Model Details
ID
anthropic/claude-sonnet-5-free
Provider
ZenMuxFamily
claude-sonnet
Release Date
Jun 30, 2026
Knowledge Cutoff
Jan 31, 2026
API Integration
NPM Package
@ai-sdk/openai-compatible
Environment Variables
ZENMUX_API_KEY
API Base URL
https://zenmux.ai/api/v1