Do they use the same underlying mechanism?

Yes. Both give the model more reasoning steps before it answers. Extended Thinking is the name for this in the Claude app; `/effort` is how you control it in Claude Code.

Is higher effort always better?

No. Extra thinking on a simple task just makes you wait. The gain shows up on genuinely hard problems — multi-step reasoning, subtle bugs, complex planning. For quick edits, leave effort at the default.

What's the difference between effort levels?

In Claude Code, `/effort low` means quick and light, `high` is the everyday default, and `xhigh` gives maximum reasoning depth. Pick based on the difficulty of the task in front of you.

Extended Thinking vs Effort in Claude

If you use both the Claude app and Claude Code, you’ve seen two different names for what sounds like the same thing: Extended Thinking in the app, and /effort in the terminal. They are the same underlying idea, just surfaced differently.

The one-line version

Extended Thinking is the Claude app’s toggle for deep reasoning before answering.
/effort is Claude Code’s dial for the same thing — how much thinking Claude does before it acts.

Extended Thinking — the app toggle

In the Claude web or desktop app, you can turn on Extended Thinking for a conversation. When it’s on, Claude works through the problem step-by-step before giving you the answer — visible as a “thinking” phase.

It’s a binary choice in the app: on or off.

Best for: hard math, logic puzzles, careful planning, anything where a quick answer tends to be wrong.

Effort — the terminal dial

In Claude Code, you control the same capability with /effort:

/effort xhigh

But instead of on/off, you get a spectrum:

low — light touch, quick answers. Good for simple tasks.
high — the default. Right for most work.
xhigh — maximum reasoning depth. For the hard stuff.

There’s also /fast, which trades a bit of cost for noticeably faster output — the other direction on the speed/depth spectrum.

Side by side

	Extended Thinking (app)	Effort (Claude Code)
Surface	Claude app (web/desktop)	Claude Code (terminal)
Control	On / off	Spectrum: low → high → xhigh
What it does	More reasoning before answering	More reasoning before acting
Default	Off (you opt in)	High (already engaged)
Best for	Hard questions in conversation	Hard coding/engineering tasks
Speed cost	Slower when on	Slower at xhigh, faster at low

The practical advice

The rule is the same in both surfaces: match the thinking to the difficulty.

Quick question, simple task → default effort / Extended Thinking off
Hard problem, subtle bug, complex plan → /effort xhigh / Extended Thinking on
Batch of easy tasks → /effort low or /fast — don’t overthink the trivial

The mistake people make is leaving it at the extremes. Maximum thinking on every task wastes time. Minimum thinking on hard tasks wastes attempts. The skill is noticing when a problem deserves more thought — and giving it.