QUICK VERDICT — AUGUST 2, 2026
● Price: V4 Flash $0.14/M input vs Sonnet 5 $2/M (14× cheaper)
● Agentic coding: V4 Flash — Terminal-Bench 82.7%, purpose-built
● Writing quality: Sonnet 5 — best in class, adaptive thinking, 128K output
● Data residency: Sonnet 5 — Anthropic US. V4 Flash API — DeepSeek China connection (self-host on MIT weights to resolve)
● Deadline: Sonnet 5 at $2/M through August 31 only
● Open weights: V4 Flash — MIT, HuggingFace. Sonnet 5 — closed.
V4 Flash 0731 for: High-volume agentic coding at the lowest possible cost. Codex-compatible, Responses API native, MIT weights for self-hosting. 14× cheaper than Sonnet 5 at intro pricing, 21× cheaper at standard. Data residency concern resolved by self-hosting the MIT weights on Western cloud.
Claude Sonnet 5 for: Writing, analysis, complex instruction following, and any task where the quality ceiling of the best Anthropic mid-tier matters. Front-load before August 31 at $2/M. Enable prompt caching if you have a stable system prompt. Measure the tokenizer uplift on your specific content type before September 1.
Last updated August 2, 2026. Related: V4 Flash 0731 full review → · Sonnet 5 pricing deadline →
⚖ Our Verdict
V4 Flash 0731 wins on price (14× cheaper), agentic coding (Terminal-Bench 82.7%), open weights (MIT), and Codex compatibility. Sonnet 5 wins on writing quality, 128K output, adaptive thinking, US data residency, and complex analysis. Not substitutes — route agentic coding to V4 Flash, writing and analysis to Sonnet 5. Act on Sonnet 5 before August 31 to lock in $2/M.