Breaking

OpenAI Begins GPT-6 Astra Rollout Two Days After Anthropic’s Claude Fable 5.1

September 3, 2026 at 17:17 EDT

Foundation Models
AI Agents
Software Dev & Coding

OpenAI has started a limited rollout of GPT-6 Astra, its new flagship model for computer use, coding, and professional work, two days after Anthropic released Claude Fable 5.1 and Claude Mythos 5.1—putting the two labs in a direct contest at the same $10 input and $50 output list price per million tokens.

September 2026 · Anthropic · OpenAI

Two labs. Two days. Same $10 / $50 sticker.

Anthropic shipped Claude Fable 5.1 and Mythos 5.1 on September 1. OpenAI answered on September 3 with GPT-6 Astra, a computer-use flagship rolling out first to limited organizations.

Terminal-Bench-Science 0.1

Agentic science scores, drawn to scale

22.4%

GPT-5.6 Sol

24.7%

Fable 5

52.6%

Fable 5.1

64.6%

GPT-6 Astra

Fable 5.1 more than doubles Fable 5 on this test; Astra leads the published comparison.

98%

Astra on FrontierMath Tier 4

100%

Astra on ExploitBench

25%

Typical Fable 5.1 bill cut vs Fable 5

47%

Less OSWorld time vs GPT-5.6 Sol

OSWorld 2.0 time per task

75 min

GPT-5.6 Sol

~40 min

GPT-6 Astra (72.6%)

Shorter column, faster task: Astra finishes the same desktop-agent eval in about 47% less time.

What users like

Fable 5.1 is being adopted for long coding jobs and cheaper cache-heavy agents. Testers say Astra now competes on computer use and one-shot generation after GPT models had trailed.

What still worries

Astra is OpenAI’s first Critical cyber model; full exploit tools stay gated. ARC-AGI-3’s 99.9% needs a provider adapter (62.7% on the standard harness). Independent score checks are still pending.

Access is gated on purpose

The most capable cyber and biology tools are not general-availability features.

Fable 5.1

Generally available; exploit work still redirected

Mythos 5.1

Trusted access only, U.S. organizations for now

GPT-6 Astra

Limited orgs today; Enterprise off by default

Release flow

1. Sep 1
Fable 5.1 / Mythos 5.1 ship

→

2. Sep 3
Astra to limited organizations

→

3. Coming days
Plus, Pro, API, AWS, Foundry

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