Frontier AI keeps racing despite calls to slow down

Despite a July open letter from AI company employees calling for frontier AI labs to slow their pace of development, a message echoed by Anthropic CEO Dario Amodei earlier this month, major model releases continue to appear at quite a clip.

Anthropic and OpenAI each released new versions of their Claude and GPT models on Tuesday: Opus 5.5 and GPT-6 Sol and Luna.

"We must slow the pace at which we improve the capabilities of AI models," said Amodei in an online post on September 12, 2026, reiterating the message from AI staff who put their names to "Pacing the Frontier." Ten days later, Anthropic celebrated the arrival of Opus 5.5, calling it "the strongest-performing model we’ve tested to date." The model arrives just 21 days after the release of Fable 5.1 and Mythos 5.1, which followed Opus 5 by 39 days.

Overall, the cadence of Anthropic model releases has accelerated from roughly every quarter in 2025 to almost monthly in 2026.

OpenAI's release cycle slowed somewhat after a flurry of releases early this year.

The upstart delivered several model variants in February and March, followed by GPT-5.5 in April.

77 days later, on July 9, GPT-5.6 reached general availability.

GPT-6 Astra debuted September 3, 2026, followed by GPT-6 Sol and Luna 19 days later.

The competitive releases from the two rival companies arrive as both prepare for initial public offerings.

For Anthropic, that could happen before the end of the year, while OpenAI isn't expected to go public until 2027.

Opus 5.5 performs better than its predecessor on software tasks, according to Anthropic, which said the model allows speedy code migrations and can reduce software load times.

Artificial Analysis puts Opus 5.5 on par with GPT-6 Astra for agentic work.

The Claude model has taken the top spot in the Artificial Analysis Intelligence Index with a score of 58, based on performance on 10 different benchmark evaluations.

With great power also comes great responsibility – Anthropic says Opus 5.5 is comparable to Mythos 5.1 in cybersecurity and biology, so it too can fall back to earlier models when safeguards kick in.