Claude Sonnet 4.5

Anthropic · September 2025

An earlier Sonnet for writing and code. Reads a fifth of what 4.6 and later hold.

Best for: Coding and deep reasoning
Superseded by: Claude Sonnet 4.6

Context window
200,000 tokens
≈ 150,000 words · about 600 pages
Max output
64,000 tokens
≈ 48,000 words in a single answer
Knowledge cutoff
January 2025
its training cutoff

Modalities

TextInput and output
ImageInput only
AudioNot supported
VideoNot supported

Features

StreamingSupported
Function callingSupported
Structured outputsSupported
Fine-tuningNot supported

Tools

Web searchSupported
Code interpreterSupported

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