OpenAI、次週に GPT-5.6 モデルの公開を準備（2 分読了）

OpenAI looks set to widen its GPT-5 line next week, with the GPT-5.6 family poised for a Tuesday arrival. The plan appears to span the standard model, potentially alongside Mini and Pro variants, landing together rather than trickling out, though the company's recent habit of staggering ChatGPT, API, and Pro releases across several days leaves room for doubt on that point.

Early traces of a GPT-5.6 Pro build have surfaced for some Pro subscribers, and the first outputs we managed to pull looked strong.

The competitive angle is hard to miss. Chatter places GPT-5.6 against Anthropic's top tier, with developers claiming it edges out the Mythos line on agentic coding work. Rumored gains center on a context window pushed toward 1.5 million tokens, up from the million GPT-5.5 shipped with in April, plus sharper long-horizon coding and quicker Codex response times. Pricing is the quieter story: OpenAI already undercuts Anthropic by roughly half on tokens, and reports point to deeper cuts aimed at a price war.

Timing sharpens the stakes. Anthropic's Claude Fable 5, a Mythos-tier model, is subject to a US regulatory action that has left its availability uncertain. A window has opened, and OpenAI looks intent on using it. Whether Washington's posture shifts again is the open variable, but the launch calendar reads as set.

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The family is not the only thing in motion. A next-generation voice model, working name GPT-Bidi-1, is also expected to land, bringing a bidirectional audio system built to listen and speak at once, ride over interruptions, and adjust mid-sentence. Inside ChatGPT, it would sit beside today's Advanced Voice Mode as a separate option, carrying High, Medium, and Instant tiers that mirror the text side. A draggable voice bubble spotted in the interface appears to be an early piece of that redesign.