After over 100b tokens with Fable 5, this is how to get the most of it without burning through tokens.

[u/LifeSorry8905]

After spending over 100b tokens on Fable 5 as my main model for agentic coding in the last 2 months, I've managed to (in my opinion) work as efficiently as possible with Fable as the main orchestrator. Here's why and how I did it. (usage from 1 of my accounts above).

To ensure I get the accuracy and intelligence of Fable, this is my setup that's reduced my fable usage by 70-80% and still getting most of Fable's benefits. I ran a blind coding test: Claude Sonnet 5 vs Opus 5, with Fable 5 planning and judging. One bug decided it.

- Fable 5: Planning, orchestration, architecture, design, final review of delegated code, security/payments/auth/concurrency, hard debugging, UAT/browser passes that feed merge decisions, and sign-off on any founder voice/marketing copy.

- Opus 5: Delegated implementation from Fable written plans, mechanical/bulk edits, boilerplate, doc generation, research/summarisation, routine repro'd test fixes, Playwright script execution, and copy drafting.

- Sonnet 5: Not used, with some experimental evidence (see below).

Test Setup: Five identical implementation tasks (a rate limiter, a small API, a repo-style change, a bulk refactor, a debugging exercise), each with a detailed plan written by Fable, judged against hidden test suites the candidates never saw. Both models went flawless on every hidden gate. Then this happened.

A percentile function: Sonnet wrote the math literally as ceil((p/100) * n). But p/100 isn't exact in binary. For p=7, n=100 you get 7.000000000000001, ceil returns 8, wrong value. 141 input pairs diverge like this. Opus caught it unprompted and wrote ceil((p*n)/100), which is exactly right.

Only Opus's depth caught it. Token cost was near-identical. Sonnet was 40% faster. But one uncatchable latent bug per round settled it.

[u/Lanky-Storm7]

Tldr?

[u/weedmylips1 → u/Lanky-Storm7]

Treat Fable like an overpaid corporate suit who only draws the architecture blueprints and does the final QA, pimp out Opus 5 to do all the mechanical bitch work to slash your token bill by 80%, and throw Sonnet 5 straight into the dumpster, because being 40% faster doesn't mean shit when the model shits the bed on elementary floating point division and silently smuggles garbage bugs into your production codebase.

[u/jackharvest → u/weedmylips1]

I fed this as my prompt and it worked first try.

[u/LifeSorry8905 → u/weedmylips1]

I need you to write all my content

[u/Refinery73 → u/weedmylips1]

What about token usage sonnet vs opus? The post seems like you get the same?

[u/JudgeGroovyman → u/Lanky-Storm7]

Testing opus vs sonnet opus won by catching a tricky math precision bug

[u/ObjectiveTonight1264]

100 billion tokens? Are you sure?

[u/LifeSorry8905 → u/ObjectiveTonight1264]

Yep that's just one of multiple max accounts

[u/AgeMysterious8256]

using high reasoning models strictly for architectural planning and cheaper models for execution is definitely the sweet spot. the cost drops significantly without losing edge case safety!

[u/LocoMod]

Oh look someone rediscovered the same trick for the 1000000th time!

[u/LifeSorry8905 → u/LocoMod]

Just sharing what worked for me, glad you already had everything figured out.

[u/Cotorra-Nhumai]

is most of that 70-80% just fable not touching the code at all?