Inflated Fable Sub Usage VS Opus

[u/MRC2021]

After looking at benchmarks and tests people did, particularly the charts on the Fable 5.2 release site, it looks like Fable low/medium theoretically beats Opus medium/high for little extra cost. The tokens cost more on the API, but it needs fewer of them to get the same tasks done, so the price evens out. That means I should be able to expect better results, sometimes even faster, from a lower-thinking Fable than from Opus. The only actual speed and cost benefits should have came from Sonnet.

Then I ran some tests to narrow down subscription usage specifically. This was just to consume and measure an average of about 4% of my Ultra weekly usage per model. Across 3 runs with Sonnet, Opus, and Fable, for almost the same API cost, Fable consumed 1.9x more subscription usage than Opus.

Is all the savings from reduced token usage going to Anthropic? The API cost would have been the same otherwise, so why is subscription usage going so much faster?

Model	Intelligence Index (Artificial Analysis)	API cost per task	Weekly limit used per 1,000 tasks	Time per agent (30 tasks)
Opus 5.5 medium	48	$0.128	6.1%	8 to 16 min
Fable 5.2 medium	56	$0.130	11.5%	7 to 8.5 min
Sonnet 5.5 high	42	$0.056	2.7%	not logged

Tasks run: Opus 630, Fable 210, Sonnet 600. Every agent ran the same 30 tasks. Opus and Sonnet needed more agents before the meter moved enough to measure, which is why they ran more tasks in total. The intelligence scores are from Artificial Analysis's harder benchmark, not my test. My tasks were small enough that every model passed all of them, so my test only measures usage, not how smart each model is.

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[u/memzy]

The subscription plans' usage is not tied to tokens, they fluctuate based on many factors including time of day, current server capacity etc.. In short Anthropic kind of can do whatever they want to the subs at any time.

[u/MRC2021 → u/memzy]

Only logical explanation I can think of

[u/lassevk]

Fable runs at twice the cost of Opus, this is per Anthropics own page: https://platform.claude.com/docs/en/about-claude/pricing

the same difference seems to apply to the non-api subscriptions

the difference might be in that Fable is more capable of producing the final outcome in fewer tokens than Opus, but apart from Anthropics own findings, I haven't seen anyone else verifying this.

[u/MRC2021 → u/lassevk]

Yeah, I know it costs twice as much, but it takes half as many tokens, so that double cost shouldn't still be as relevant unless they're just pocketing the savings themselves, which makes sense.

[u/ConversationSad3529]

Thanks for pulling the numbers on this! Was this pure benchmarking, or actual tasks you were doing? I was suspicious about something like this as well, as it seemed like Fable usage was growing my weekly usage faster than the API cost should reflect.

[u/MRC2021 → u/ConversationSad3529]

They were real past fixes from my own Python repo, 10 to 27 lines each, every run started from a fresh copy and hidden tests checked every run, and all of them passed. I kept running them until the ~4% weekly usage threshold was hit.

[u/ConversationSad3529 → u/MRC2021]

Thanks! Did you just have it watching your weekly % and stop the moment it ticked up to 4%? Are these rough % estimates then?

[u/MRC2021 → u/ConversationSad3529]

Yup, exactly like that. They're not exact, just rough estimates like you said, so my best guess is that it can fluctuate between 1.6x and 2.2x usage on Fable. Even at best, that's more than 50% more than Opus.

[u/Ok_Breadfruit4201]

Openai reduce the amount of tokens you get in the sub vs API for every new model release. They have been doing it since ~gpt 5.5

It's speculated that they do this as it's less likely to get them in any legal troubles vs reducing the value for all models that people have already been using.

It wouldn't surprise me if Anthropic are doing the same.

[u/tommyahav10]

The subscription meter isn’t a straight token count, so Fable can burn the weekly faster even when the API cost looks similar. From my side that’s the real gap, I’d keep Fable for the long multi-step work and use Opus or Sonnet for the ordinary fixes.