A team runs an interactive live-debugging assistant on Claude Opus. Users complain that responses stream too slowly during sessions. The team…

Fast mode is the best fit because the workload is interactive, latency-sensitive, and wants to preserve Opus-level reasoning quality. The Message Batches API is for asynchronous high-throughput processing, not live streaming/debugging. Extended thinking can improve deliberation but adds thinking time before/while responding. Downgrading to the smallest model may reduce latency but risks the reasoning-quality loss the team explicitly wants to avoid.

A. Message Batches is asynchronous throughput optimization, not a solution for interactive streaming latency.

B. Extended thinking generally increases reasoning time and is not intended to make live responses stream faster.

D. Claude model tiers are not equivalent; smaller models can trade reasoning quality for speed/cost.

- Anthropic Docs, “Claude models / Opus fast mode,” section describing faster Opus output via speed: "fast" with premium pricing.

- Anthropic Docs, “Message Batches API,” Overview: batches are asynchronous and intended for large-volume processing rather than immediate interactive responses.

- Anthropic Docs, “Extended thinking,” Overview and usage guidance: extended thinking lets Claude spend additional reasoning effort before producing an answer.

- Anthropic Docs, “Models overview,” model comparison table: model tiers differ in intelligence, speed, and cost.