Claude Opus 5.5 vs Fable 5.1: How I Split Them

	Opus 5.5	Fable 5.1
Anthropic's own label	Long-running agentic coding and knowledge work	Demanding reasoning and long-horizon agentic work
What I use it for	Coding	Emails, writing, research, reading documents, client work
API price per million tokens (input / output)	$4 / $20	$10 / $50
Speed, per Anthropic	Moderate	Slower
Default effort on the API	Medium	High
Context window	1M tokens	1M tokens
On the Pro pricing table	Included	Usage credits
When I hit the Pro limit	After 1 to 2 hours	After 2 to 4 hours

Prices and labels are from Anthropic's models overview and pricing page, read on 30 September 2026.

My numbers on Pro

I'm on Claude Pro and use both models on it. Opus 5.5 does my coding. Fable 5.1 does everything else: writing emails, research, reading documents and client work. On Opus I hit the Pro usage limit after 1 to 2 hours of work. On Fable it took 2 to 4 hours. When I ran out, I stopped work and waited for the limit to reset before I could carry on.

Those two numbers are not a clean race. My Opus hours were coding and my Fable hours were writing and reading, so the jobs were different. I can only tell you what happened on my account with the work I gave each one.

The price list points the other way, since Fable is the dearer model on the API.

The API gap is 2.5 times

If you pay per token, the choice is simpler. Fable 5.1 costs 2.5 times as much as Opus 5.5 for both input and output. Anthropic's own advice on its models page is to start with Opus 5.5 for most work, and to move to Fable only when Opus at a higher effort still falls short.

The Pro plan is $20 billed monthly or $17 a month on the $200 annual plan. On the pricing table, the Pro column for Fable reads "Usage credits", while the two Max columns read "50% of weekly limits". I paid usage credits for Fable on top of my plan, so check that row before you plan a full working day around it on Pro.

How I decide which one gets a job

Code goes to Opus. That matches Anthropic's label for it, and it is also the cheaper of the two on the API.

Writing, emails, research, documents and client work go to Fable. My inbox is already connected to Claude, which I set up the way I describe in how I connected Gmail and Calendar to Claude Pro.

The downside is the waiting

On the $20 plan, the usage limit is what slows me down. When it hits, the work stops, and I waited for the reset.

Anthropic's pricing page says limits run on a rolling five-hour window, and paid plans have a weekly limit on top of that. So a long coding session on Opus can end in the middle of the task, and your fix is to wait or to pay more. If you code for most of the day, plan for that before you pick Pro.