How We’d Choose Between the Brand-New OpenAI and Anthropic Models

Every’s team tested GPT-5.3 Codex and Opus 4.6 on release day across real production use cases. Their central finding: the models are converging. Opus 4.6 retains its predecessor’s warmth and agency while gaining the precision that made Codex dominant for hard coding. Codex 5.3 kept its workhorse reliability but picked up Opus-style fluidity. Both labs appear to be building toward a single archetype — fast, deeply technical, yet pleasant to collaborate with.

The free-tier summary breaks the comparison into research/planning, long feature builds, and empathy/creativity. Full Reach Test ratings from six internal team members (Kieran Klaassen, Naveen Naidu, Katie Parrott, Andrey Galko, Dan Shipper) are behind the paywall, along with custom internal benchmarks graded by task difficulty.

RDCO mapping: Directly relevant to our tooling decisions. The convergence thesis aligns with our experience running both models in the autonomous agent loop — switching costs between providers keep falling, which supports our multi-model routing architecture.