GPT-6 Astra

GPT-6 Astra, released September 3, 2026, opened OpenAI's GPT-6 generation and was the company's first new general-purpose flagship since the three-model GPT-5.6 family — Sol, Terra and Luna — arrived on June 26, 2026. OpenAI had trailed the model for a month before launch without ever announcing it as a product: on August 1, 2026 it named Astra "our next major model" in a research post, reporting that an internal version had produced new results on ten long-standing open mathematical problems, each with a machine-checkable proof in the Lean theorem prover. Capability demonstrated in a paper before a model existed to sell was an unusual way to introduce a flagship, and it set the terms for the four weeks that followed.

The launch table led on reasoning: 99.9% on ARC-AGI-3, against the 30.2% Claude Opus 5 had posted on the same interactive-environment board in July, 97.6% on the rebuilt second edition of FrontierMath Tier 4, and 96.0% on GPQA Diamond. Agentic work moved by similar margins — 64.6% on Terminal-Bench Science 0.1 and 41.4% on AutomationBench, both more than double GPT-5.6 Sol's figures in the same run, and 74.1% on DeepSWE v1.1. The security rows are the ones that explain the wait: 100.0% on ExploitBench, the Carnegie Mellon capability ladder that scores how far a model gets turning a known V8 bug into a working exploit, and 99.2% on SRE-Bench over four attempts.

The professional and coding tables ran closer. At launch, OpenAI reported Astra at 57.9% on Terminal-Bench 4.0 against Claude Fable 5.1's 55.8%, BrowseComp at 91.5%, and 0.84 on the OpenScore String Quartets sheet-music transcription set where GPT-5.6 Sol had managed 0.19 — but on FrontierCode 1.1 its 53.3% on the main split and 64.5% on the extended set both sat fractionally behind the Claude models OpenAI ran beside it, and it trailed on Artificial Analysis' two composite indices: 61.2 on the Intelligence Index against Fable 5.1's 65.7, and 67.0 on the Coding Agent Index. For a generational release the shape of the table was lopsided — enormous margins on reasoning, security and the internal professional sets, and a coding field the previous generation had already crowded.

That capability is what OpenAI spent August evaluating. On August 7 the company said it had paused parts of the work on Astra because preliminary results could not rule out that the model reached the Critical cybersecurity level in its Preparedness Framework — the threshold describing a model able to find and carry out attacks against well-defended systems without human help, and the first time OpenAI had put one of its own models in that bracket. It returned to the question on September 1 in "Path to Astra: critical capabilities and frontier safeguards", saying the further evaluations were complete and the safeguards it had built around the model were sufficient to ship. Astra launched two days later.