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Claude Sonnet 4

Anthropic · Claude Sonnet line · lightweight

Released May 22, 2025Replaced by Claude Sonnet 4.5

Claude Sonnet 4 was released by Anthropic on May 22, 2025, as a lightweight model in the Claude Sonnet line.

What changed

Anthropic's upgrade to Claude Sonnet 3.7 for coding and reasoning, 65% less likely to take shortcuts on agentic tasks, made available to free users at the same API price.

Sources: Anthropic

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Where the Claude Sonnet line stands

Claude Sonnet 5.5 is the current model in this line. The card shows how long it has been since the last release against the line's usual gap and its recent ones — the rhythm, not a date.

Claude Sonnet

Anthropic · lightweight line

Latest: Claude Sonnet 5.5 · Sep 28, 2026

Just released26 days since the last release · usual gap 130 days

Scores 18 points higher than Sonnet 5 on the all-round intelligence index and runs over 30% faster, at the same $2 / $10 price per 1M tokens.

What changed in Claude Sonnet 5.5 →
Days since last release
26
days
Usual gap
130
days
Recent gaps
Claude Sonnet 5.5 · Sep 2026
90
Claude Sonnet 5 · Jun 2026
133
Claude Sonnet 4.6 · Feb 2026
141
Claude Sonnet 4.5 · Sep 2025
130

Every Claude Sonnet release

Newest first. See the full line with every card →

  1. Sep 28, 2026Claude Sonnet 5.5
  2. Jun 30, 2026Claude Sonnet 5
  3. Feb 17, 2026Claude Sonnet 4.6
  4. Sep 29, 2025Claude Sonnet 4.5
  5. May 22, 2025Claude Sonnet 4 · this page
  6. Feb 24, 2025Claude 3.7 Sonnet
  7. Oct 22, 2024Claude 3.5 Sonnet (new)
  8. Jun 20, 2024Claude 3.5 Sonnet
  9. Mar 4, 2024Claude 3 Sonnet