David Ondrej tests GPT 5.5 against Claude Opus models

David Ondrej covers the release of GPT 5.5, which OpenAI positioned as a competitor to Anthropic's unreleased "Mythos" model. GPT 5.5 was made available first to Pro users, and Ondrej tests it inside the Codex app, noting it is reportedly strong at SVG graphics, 3D, and front-end web development. He argues that Anthropic has suffered reputation damage recently — first by not releasing Mythos, then through user-reported regressions in Opus 4.7 — and that OpenAI's heavier investment in compute infrastructure gives it an opportunity to overtake Anthropic in 2026. Ondrej states he personally still prefers Opus 4.6 over 4.7 for daily coding work, citing 4.7's lack of a fast mode and inconsistent instruction-following.