🧭 Which Claude Model To Pick (And When To Let It Think)

There’s a small menu in Claude that most people have never opened, or opened once, panicked and closed. It sits next to the send button, in the chat box, and it holds three settings: which model you’re talking to, how much effort it puts in, and whether it thinks before it answers.

Five minutes and it stops being a mystery. Knowing this changes what you get out of Claude, and how far your allowance stretches.

What’s actually in the menu

The list depends on your plan. At the time of writing (September 2026):

• Claude Sonnet 5 is the everyday default. Writing, planning, client emails, analysis, real work. Staying here forever is a completely fine life.
• Claude Haiku 4.5 is the quick, light one. Reword this, what’s this acronym, turn this list into a table. Fast answers, and gentler on your allowance.
• Claude Opus 5.5 is the heavyweight, and the paid plan (Pro, around £20 a month) is where you’ll find it. Slower, and noticeably better at genuinely hard things: long tangled documents, work where the reasoning has many steps that all have to hold hands.
• Claude Fable 5 is a tier above Opus, built for the hardest work. If it isn’t in your menu, you’re not missing anything for everyday jobs.

Names change. Anthropic ships new versions faster than anyone updates their guides, including me. What doesn’t change is the shape of the list: a quick one, an everyday one, a heavyweight, and the menu next to the send button where you swap between them.

The other two settings in the same menu

Effort is how hard Claude thinks before answering. Turn it down for quick factual jobs and your allowance goes further. Turn it up for the one task today that actually matters. For most everyday jobs, leave it where it is.

Thinking is the toggle that lets it work the problem through before it starts writing.

• Worth it: comparing contracts, a pricing rethink, a plan with lots of moving parts, anything where you’d tell a person “have a proper think and come back to me”.
• Not worth it: drafting, rewording, summarising. You’ll wait longer for an answer that isn’t better. If you’d expect a person to answer straight away, leave it off.

The habit that beats fiddling

Stay on the default and describe the job honestly. “This one’s tricky, take your time and think it through properly” does most of what menu-fiddling does, without the menu. Model-fiddling is a hobby. Describing your task properly is a skill.

And when you genuinely can’t tell, ask.

Nick this one:

You're helping me pick a setting rather than fiddle with menus. Here's the job: [for example "compare three suppliers' terms and pricing before I move my whole business over, about 40 pages, real money riding on the difference" or "reword a chase-up email to a client who's three weeks late paying"]. I'm on the [free / paid] plan.

Tell me:
1. Which model in my picker to use for this, and why, in one line.
2. What to set the effort to, and what that costs me in speed and allowance.
3. Whether thinking is worth switching on for this one.
4. One sentence I can save as my rule for jobs like this, so I don't have to ask again.

Rules: plain English, under 120 words, no hedging. If you can't tell how hard the job is from my description, say so. Ask me up to three questions before you start.

That last output is the point. Ten of those sentences and you never open the menu again.

The honest bit

Heavier models and higher effort eat your allowance faster. Making them your default is how people end up mystified about hitting limits at 2pm. Nothing’s broken, you were just being thorough about a shopping list.

The names in this guide will shuffle. That’s why it teaches where the menu lives and what the three settings do, rather than screenshots.

No setting fixes a vague ask. A lazy prompt to the heavyweight model is the most expensive way to get a mediocre answer that exists.

Today

Open the menu, just to look. Knowing where it lives is half the intimidation gone. Then next time you’ve got one genuinely hard job, switch to the heavier model with thinking on, once, on something real. You’ll feel the difference and you’ll know exactly what it’s for.

If the words around the menu threw you, the full list is Every AI Word That’s Been Confusing You, Explained.

That’s one menu understood. The Claude Kickstart is the rest of the setup: Claude taught your actual work, five real jobs off your plate, and a playbook for your trade. £47, one weekend.