# Effort vs fast mode

> Fast mode buys up to 2.5x speed on Opus for a flat ~2x per-token premium with no quality change; lower effort cuts tokens and sometimes quality. They stack.

URL: https://bartlomiejkrupa.dev/notes/effort-vs-fast-mode/
Category: rule | Updated: 2026-10-07
Summary: Fast mode buys up to 2.5x speed on Opus for a flat ~2x per-token premium with no quality change; lower effort cuts tokens and sometimes quality. They stack.

Effort level and fast mode are independent Claude controls. Effort scales how many tokens the model spends on text, tool calls, and thinking. Fast mode keeps quality identical and pays a flat latency premium - $8/$40 per million tokens on Opus 5.5 (standard $4/$20) and $10/$50 on Opus 5 and Opus 4.8 (standard $5/$25) - for up to 2.5x speed.

## Rule

| Lever | What changes | Cost effect |
| --- | --- | --- |
| Effort | Token spend (and sometimes quality) | Lower effort = fewer tokens |
| Fast mode | Latency only | Flat ~2x premium: $8/$40 on Opus 5.5, $10/$50 on Opus 5 / 4.8 |

- Stack **low effort + fast mode** for a simple, latency-sensitive task.
- For quality-critical work, **drop fast mode and raise effort** - paying more per token for identical output makes no sense next to a dial that changes what the model produces.
- Fast mode on Opus 4.7 was removed 2026-07-24; migrate to Opus 5.5, Opus 5, or Opus 4.8.
- Opus 5.5, Sonnet 5.5, and the Fable models cannot disable thinking; on adaptive models, effort is the real depth dial.

Controls: `/effort`, `--effort`, `CLAUDE_CODE_EFFORT_LEVEL`, `effortLevel` in settings; `/fast` or `"fastMode": true`. The first fast-mode message in a conversation pays the full uncached fast-mode input price for the entire existing context - turn it on at session start, not mid-way.

Full playbook: [Why fast mode isn't a lower effort level](/articles/claude-effort-thinking-fast-mode). Tier choice sits underneath both: [Why most agents default to the wrong Claude tier](/articles/claude-model-tier-comparison).

Sources:
- Speed up responses with fast mode: https://code.claude.com/docs/en/fast-mode
- Pricing: https://platform.claude.com/docs/en/about-claude/pricing
- Effort: https://platform.claude.com/docs/en/build-with-claude/effort
- Model configuration: https://code.claude.com/docs/en/model-config