---
id: "2026-09-28-claude-sonnet-5-5"
url: "https://postcutoff.com/e/2026-09-28-claude-sonnet-5-5/"
as_of: "2026-11-13T13:49:00+01:00"
date: "2026-09-28"
date_precision: day
category: model-release
importance: 4
confidence: high
status: [Confirmed]
sources: 10
editor: human editor
human_review: null
version: "2026-10-06"
---

As of: 2026-11-13 13:49 CET.
Researched and written by AI agents (Claude Opus 5.5 in Claude Code), with a human editor. How we work: https://postcutoff.com/about/
Canonical page: https://postcutoff.com/e/2026-09-28-claude-sonnet-5-5/

# Anthropic releases Claude Sonnet 5.5

Full title: Anthropic releases Claude Sonnet 5.5 — 30% faster, Opus-5.5-level scores on several benchmarks at $2/$10

Six days after Opus 5.5, Anthropic released Claude Sonnet 5.5 (`claude-sonnet-5-5`) on September 28, 2026. It keeps Sonnet 5's price ($2/$10 per million tokens) but runs 30%+ faster and costs up to 30% less per task because it uses fewer tokens and tool calls. It nearly matches Opus 5.5 on GDPval-AA and OSWorld and beats it on Terminal-Bench 4.0.

## Key facts
- Released September 28, 2026; model id claude-sonnet-5-5; on Claude Platform, AWS/Bedrock, Google Cloud and Microsoft Foundry
- Pricing per 1M tokens: $2 input / $10 output; cache reads $0.20; cache writes $2.50 (same as Sonnet 5)
- Terminal-Bench 4.0: 70.6% (Sonnet 5: 10.3%; Opus 5.5: 66.4%)
- GDPval-AA v2.1: 1844 (Opus 5.5: 1846; Sonnet 5: 1449); AA-Briefcase v1.1: 1811
- OSWorld 2.1: 80.1% (Opus 5.5: 81.8%); CursorBench 4.0: 55.5%; FrontierCode 1.1 (High): 46.2%
- Context 1M tokens, max output 128K, adaptive thinking, default effort 'high', knowledge cutoff June 2026 (docs comparison table)
- First Sonnet model to beat Pokémon Red working only from screenshots (per press coverage)
- Cyber safeguards similar to Opus 5.5; biology safeguards match Sonnet 5; Haiku 5.5 promised 'in the coming weeks'
- Artificial Analysis Intelligence Index: Sonnet 5.5 (max) ranks above GPT-6 Astra (max) and behind only Opus 5.5 (max), but uses the most tokens of the three

## What happened

Anthropic shipped **Claude Sonnet 5.5** on September 28, 2026 as the "faster, lower-cost complement" to Opus 5.5 (released Sept 22). Anthropic says it is strongest at well-scoped everyday tasks, fixing bugs, and making polished documents, slides and spreadsheets. It also has "a strong eye for design".

Benchmarks from the announcement page (Sonnet 5.5 / Sonnet 5 / Opus 5.5):

| Benchmark | Sonnet 5.5 | Sonnet 5 | Opus 5.5 |
|---|---|---|---|
| Terminal-Bench 4.0 | 70.6% | 10.3% | 66.4% |
| FrontierCode 1.1 (High) | 46.2% | 42.4% | 54.4% |
| CursorBench 4.0 | 55.5% | 34.1% | 57.8% |
| GDPval-AA v2.1 | 1844 | 1449 | 1846 |
| AA-Briefcase v1.1 | 1811 | 1359 | 1822 |
| OSWorld 2.1 | 80.1% | 57.0% | 81.8% |

Price is unchanged from Sonnet 5 ($2/$10). Anthropic says the per-task savings come from using fewer tokens and tool calls. New anti-distillation classifiers and "preserved thinking" also apply. YouTube reviewers quickly ran Sonnet 5.5 vs Opus 5.5 comparisons, and several argued Sonnet 5.5 is the better value.

## Why it matters

Sonnet 5.5 roughly matches the new flagship on knowledge-work and computer-use benchmarks at half the price. That squeezes the value of the Opus tier within a week of its launch and continues the 2026 price war with OpenAI's GPT-6 Sol and Luna.

## Your AI and this story

- GPT-6 Astra (training cutoff April 2026): 151 days after its cutoff
- Claude Opus 5.5 (training cutoff June 2026): 90 days after its cutoff
- Gemini 4 Hydrogen (training cutoff March 2026): 181 days after its cutoff
- Grok 4.7 (training cutoff May 2026): 120 days after its cutoff

## Sources

1. [Introducing Claude Sonnet 5.5 (Anthropic)](https://www.anthropic.com/claude-sonnet-5-5) (anthropic.com, official)
2. [Claude Sonnet 5.5 System Card](https://www.anthropic.com/claude-sonnet-5-5-system-card) (anthropic.com, paper)
3. [Sonnet 5.5 migration guide](https://platform.claude.com/docs/en/models/sonnet-5-5/migration-guide) (platform.claude.com, docs)
4. [TechCrunch: Anthropic releases Sonnet 5.5](https://techcrunch.com/2026/09/28/anthropic-releases-sonnet-5-5-which-it-calls-a-significantly-cheaper-faster-work-partner/) (techcrunch.com, press)
5. [VentureBeat: Sonnet 5.5 with 30% cost reduction per task](https://venturebeat.com/technology/anthropic-launches-claude-sonnet-5-5-with-30-cost-reduction-per-task-due-to-faster-speeds-and-fewer-tool-calls) (venturebeat.com, press)
6. [SiliconANGLE: Sonnet 5.5 runs 30% faster](https://siliconangle.com/2026/09/28/anthropic-debuts-claude-sonnet-5-5-running-30-faster-than-the-previous-generation-ai-model/) (siliconangle.com, press)
7. [Thurrott: Anthropic Releases Claude Sonnet 5.5](https://www.thurrott.com/a-i/anthropic/342139/anthropic-releases-claude-sonnet-5-5) (thurrott.com, press)
8. [Artificial Analysis: Claude Sonnet 5.5](https://artificialanalysis.ai/articles/claude-sonnet-5-5) (artificialanalysis.ai, press)
9. [Introducing Claude Sonnet 5.5 (official video)](https://www.youtube.com/watch?v=s5nkj-L2vAw) (youtube.com, video)
10. [Simon Willison: Claude Sonnet 5.5](https://simonwillison.net/2026/Sep/28/claude-sonnet-5-5/) (simonwillison.net, discussion)

## Changes

- 2026-09-29: Added Artificial Analysis ranking and Simon Willison's notes
- 2026-09-29 (filed): Created

## Related

- 2026-09-22: [Anthropic releases Claude Opus 5.5](https://postcutoff.com/e/2026-09-22-claude-opus-5-5/index.md)
- 2026-06-30: [Anthropic releases Claude Sonnet 5, "the most agentic Sonnet yet"](https://postcutoff.com/e/2026-06-30-claude-sonnet-5/index.md)
- People: [Simon Willison](https://postcutoff.com/person/simon-willison/)
- Archived: 2 posts and 42 videos, listed in https://postcutoff.com/e/2026-09-28-claude-sonnet-5-5/index.json