API model: gpt-5.3-chat-latest available (aka "instant" on ChatGPT)

No API-only model specifically yet, but you get what was just released to ChatGPT, “experiment with the latest version with less feature support”:

gpt-5.3-chat-latest Supports: temperature: no top_p: no Real system role: no

• Unlike prior models of “chat”, currently supports sending reasoning_effort, internally: ‘minimal’:5, ‘low’:16, ‘medium’:64, and ‘high’:200. (all ineffective to get lots of thinking done for minimal tasks, but at high, up to 700/700 split of reasoning-to-seen tokens for increasing question).
• “verbosity” does have an effect: “low” is extremely low output (internal “oververbosity” of 1)

No pricing yet, but probably follows 5.3 codex, along with no cache discount for running on service_tier or batch.