How does Claude Sonnet 5's context window differ from Claude Sonnet 4.6's in practice?

The nominal context window figure, 1 million tokens, is the same maximum on both models, so on paper nothing has changed about the ceiling.

In practice, because Sonnet 5's tokenizer produces more tokens for the same text, that 1M-token window holds meaningfully less actual text than it did on Sonnet 4.6 - reporting suggests it's closer to holding the equivalent of around 770,000 Sonnet-4.6-token-equivalents worth of content.

This matters most for workloads that were already pushing close to the context limit on Sonnet 4.6, since the same document set or conversation history that fit comfortably before could now approach or exceed the window on Sonnet 5, purely due to the tokenizer change rather than any actual content growth.

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