Anthropic dropped Claude Sonnet 5.5 six days after Opus 5.5.
Anthropic
- Claude Sonnet 5.5 (Sept 28)
List price stays at $2/M in and $10/M out. It's 30% faster and uses fewer tool calls to finish tasks.
The Numbers
Agentic coding (Terminal-Bench 4.0) 70.6%. +6% over Opus 5.5 (66.4%) and +22% over GPT-6 Sol (57.9%). Sonnet 5 was at 10.3%. It beats Anthropic's own flagship from last week.
Knowledge work (GDPval-AA v2.1) 1844 Elo. Two points behind Opus 5.5 (1846) at half the price.
Computer use (OSWorld 2.1) 80.1% partial. Up from 64.0% on Sonnet 5.
Agentic coding (FrontierCode v1.1) 53.8%. Right next to Sol (54.1%) and Opus 5.5 (54.4%).
Real-world business (AA-Briefcase) 84.2%. Beats Sol (81.6%).
Gaming / GUI agents (Pokémon Red) Cleared. First Sonnet to beat Pokémon Red from just screenshots.
What r/ClaudeAI is Saying
Someone posted a console screenshot asking why Anthropic killed Opus 5.5 after six days. If you bought Opus credits last Tuesday, Sonnet 5.5 is cheaper, faster, and beats it on coding benchmarks.
Streaming in Claude Code feels a lot faster. Agent loops don't crawl anymore.
Free users on Claude.ai and GitHub Copilot get it too.
And people are already asking when Haiku 5.5 drops.
Pricing Check
Anthropic
- Sonnet 5.5: $2/M in, $10/M out. Cache reads down to $0.20/M.
- 1M context window, 128K max output tokens, Jan 2026 cutoff.
Same list price as Sonnet 5, but cheaper per task because it takes fewer steps to solve things.
Thoughts
If a $2 model beats the $4 flagship at terminal coding, you don't really need Opus for agents anymore.
Model shelf life is down to six days, lol.