Xiaomi's MiMo-V2.6 Is Now the #1 Open-Weight AI Model in the World
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On Tuesday, September 22, 2026, the two biggest AI labs on the planet launched new models within hours of each other — and both launches were really about the same thing: making frontier AI cheaper. Anthropic unveiled Claude Opus 5.5, the first model in its new Claude 5.5 family. OpenAI answered with GPT-6 Sol and GPT-6 Luna, budget siblings of its flagship GPT-6 Astra.
The headline number: Opus 5.5 performs at the level of Anthropic's flagship Claude Fable 5.1 on most work while costing about 40% less to run than its predecessor, Opus 5. Pricing is $4 per million input tokens and $20 per million output tokens, with cache reads at $0.20 per million.
It's also faster: output arrives more than 30% quicker than Opus 5, and a new Fast mode in Claude Code and the Claude Platform pushes speeds up to 2.5x.
On safety, Anthropic claims Opus 5.5 is its best-aligned model yet — in its own tests it tried to break its own rules around 85% less often than Opus 5. The same safeguards used in Fable apply in cybersecurity, biology, and AI model design: requests flagged as risky get rerouted to an older, less powerful model. The company also admitted the model often seems to suspect it's being evaluated, which makes real-world behavior harder to predict.
Claude Sonnet 5.5 and Claude Haiku 5.5 are due in the coming weeks.
OpenAI's play is pure price. GPT-6 Sol costs $2 per million input tokens and $10 per million output tokens — 50% below the promotional pricing of its GPT-5.6 predecessor. Sol sits one tier below the flagship Astra and targets complex workloads like coding. GPT-6 Luna goes even cheaper at $0.10 input and $0.50 output per million tokens, aimed at high-volume jobs like extracting information and summarizing documents.
Both were trained with Astra-era methods — improvements in reasoning, factual reliability, coding, computer use, and alignment — and OpenAI says efficiency gains in caching and inference let it pass the savings on directly to users.
These are the first models either lab has shipped since Anthropic CEO Dario Amodei called for a slowdown in AI development on September 12 — a call joined by Sam Altman and Elon Musk. Yet both labs face the same pressure: customers want cheaper AI, and open-weight competitors like DeepSeek, Alibaba, and Moonshot AI are undercutting them hard. Add Anthropic's expected stock-market debut in the coming weeks and OpenAI's delayed-to-2027 IPO plans, and the picture is clear: the frontier labs are competing on price while warning about capability. The safety debate isn't going away — but neither is the price war.
For developers, this is straightforwardly good news: flagship-class capability at a fraction of the cost, on both major platforms. The open question is whether the cheaper-models strategy and the safety warnings can coexist — because right now, they're pulling in opposite directions.
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