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Anthropic Releases Claude Opus 5.5, First of the 5.5 Series

Published: September 22, 2026 · Updated: October 10, 2026 Read time: 2 min
Anthropic Releases Claude Opus 5.5, First of the 5.5 Series

Anthropic has released Claude Opus 5.5, the first model in the Claude 5.5 series. The model tops Anthropic's BenchLM leaderboard at 86.9 as of September 29, and arrives with a roughly 20% price cut versus Opus 5.

Anthropic Releases Claude Opus 5.5, First of the 5.5 Series

Update (October 10, 2026): The series is complete: Sonnet 5.5 followed on September 28 and Haiku 5.5 on October 7 ($0.10/$0.50). The "rumors of two additional releases" discussed below are no longer rumors. Opus 5.5's BenchLM score has settled at 86.3 — still #1.

Anthropic has launched Claude Opus 5.5, the opening release of the Claude 5.5 series and the company's new flagship. The model went generally available on September 22, 2026, three weeks after OpenAI's GPT-6 Astra debut — keeping the two labs on their now-familiar staggered release cadence.

On Anthropic's own leaderboard, Opus 5.5 posts a BenchLM score of 86.9 as of September 29, making it the strongest Claude model to date. Anthropic frames the 5.5 series as its most capable Opus generation, with improvements concentrated in the areas enterprise buyers care about: long-horizon coding, multi-document reasoning, and reliable tool use inside agent frameworks.

The more notable change is economic. Opus 5.5 is priced at $4 per million input tokens and $20 per million output tokens — a cut of roughly 20% versus Claude Opus 5's $5/$25. Prompt caching gets aggressively cheaper too: cache reads drop to $0.20 per million tokens, which Anthropic says is 60% cheaper than on Opus 5, while cache writes cost $5 per million for five-minute retention or $8 for one-hour retention.

For high-volume customers, that caching price matters more than the headline rate. Workloads that reuse large system prompts or documentation blocks — customer support agents, code assistants, document analysis pipelines — can see the majority of their input tokens served from cache, effectively repricing the model far below its list rate.

Opus 5.5 lands in a lineup that Anthropic has been actively refreshing: Claude Sonnet 5 arrived in June at $2/$10, Opus 5 followed in July, and the previous-generation Sonnet 4 and Opus 4 were retired on June 15. Rumors of two additional Anthropic releases in the near term continue to circulate, consistent with the double-release pattern the company has repeated several times since 2025.