Claude Sonnet 5.5 Launch: Score and Cost vs Opus, Fable, Astra (2026)

▲ Sonnet 5.5 launch: cheapest model nearly #1

Claude Sonnet 5.5 is Anthropic's AI model released on September 28, 2026, pitched as a cheaper, faster work partner. Independent scores put it just two points behind Opus 5.5, so the question is whether the priciest model is worth it.

Why Claude Sonnet 5.5 Is Making Headlines

September brought a rush of launches: Fable 5.1 on the 1st, OpenAI's GPT-6 Astra on the 3rd, Opus 5.5 on the 22nd, and Sonnet 5.5 on the 28th. Its price matches Sonnet 5, and Anthropic says it is 30%+ faster and, in its own testing, up to 30% cheaper per task.

▲ No single winner across four models

Sonnet 5.5 vs Opus, Fable and Astra: Performance

Artificial Analysis (AA), an independent tester, scores Opus 5.5 at 58, Sonnet 56, and Fable 5.1 and Astra 53 each, all at max settings. On a real-work test (GDPval-AA), Sonnet's 1844 nearly ties Opus's 1846. Sonnet beats Opus at terminal coding, 70.6% to 66.4% per Anthropic and 63.6% to 59.6% in AA's run, but Opus leads the hardest reasoning test, 67.7% to 64.5%.

▲ Sonnet 5.5 score vs output price chart

Claude Sonnet 5.5 Pricing: Sticker Price vs Real Cost

Per 1M tokens (chunks of text an AI reads or writes), input and output cost $2/$10 for Sonnet, $4/$20 for Opus, and $10/$50 for Fable 5.1 and Astra. But AA's cost per task at max settings was Sonnet $7.60, Opus $5.98, Fable $7.63 and Astra $3.26. Anthropic reports up to 30% lower cost per task than Sonnet 5, yet AA found it about 50% costlier at max settings.

▲ Cost race joins the score race

Is AI Competition Shifting From Scores to Cost?

Opus 5.5 launched at $4/$20 per 1M tokens, a 20% cut from Opus 5, while Fable 5.1 and Astra share one $10/$50 list. VentureBeat argues the model war is no longer only about the top score, and a cost race now runs alongside it.

Key Takeaways

① Performance - Sonnet scores 56, two points behind Opus 5.5 and ahead of Fable 5.1 and Astra.

② Price - Output costs $10 per 1M tokens, one-fifth of the $50 top rate, yet Astra's cost per task ($3.26) undercuts Sonnet's ($7.60).

③ Choice - The winner changes by test, so the right pick depends on whether your work needs the best or just enough.

Choosing an AI is shifting from finding the strongest model to balancing performance and cost, and this launch shows that shift.

👉 Claude Opus 5.5 Launch: #1 on AI Index, 20% Price Cut (2026) - also worth a read.

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📌 Sources: Anthropic, TechCrunch, VentureBeat, The Next Web, Artificial Analysis, OpenAI (2026)