Claude Fable 5 vs GPT-5.6: Pricing and Cost Compared
GPT-5.6 ships in three price tiers - Sol, Terra, and Luna - while Claude Fable 5 sits at $10/$50. Here is the full cost comparison and when each is cheaper in practice.
TL;DR
On sticker price, GPT-5.6 undercuts Claude Fable 5 across the board. GPT-5.6 Sol is $5/$30 per million input/output tokens, Terra is $2.50/$15, and Luna is $1/$6 - versus Fable 5's $10/$50. But price per token is not price per finished task: a model that needs fewer turns or less verification can be cheaper overall even at a higher rate.
The Numbers
| Model | Input ($/M) | Output ($/M) |
| GPT-5.6 Sol | $5 | $30 |
| GPT-5.6 Terra | $2.50 | $15 |
| GPT-5.6 Luna | $1 | $6 |
| Claude Fable 5 | $10 | $50 |
Since July 7, 2026, Fable 5 on Claude subscription plans is billed via usage credits at that $10/$50 rate.
Sticker Price vs Total Cost
Output tokens dominate most bills. At $50/M output, Fable 5 is the priciest of the group; Sol at $30/M is 40% cheaper on output, and Luna at $6/M is an order of magnitude cheaper. For pure high-volume generation where quality is "good enough," GPT-5.6's cheaper tiers win decisively.
The counterweight is task efficiency and rework. If a cheaper model produces output that needs more retries, more human review, or - as METR flagged for Sol - carries a higher reward-hacking risk that forces independent verification, the effective cost per correct result rises. Fable 5's strong SWE-Bench Pro performance argues for fewer failed attempts on real engineering tasks.
A Simple Way to Decide
1. High-volume, low-stakes generation (drafts, classification, bulk transforms): GPT-5.6 Terra or Luna. Cheapest by far.
2. Everyday coding and reasoning: GPT-5.6 Sol for cost, Claude Sonnet 5 or Opus 4.8 for value inside a Claude plan.
3. High-stakes, correctness-critical work (production migrations, code you will ship): Claude Fable 5, where the higher rate buys leading real-world reliability.
Watch the Billing Model, Not Just the Rate
Remember that Fable 5 now requires enabled usage credits on Claude plans - set a spending cap in the Console. On the OpenAI side, the three-tier structure lets you route each task to the cheapest tier that meets quality, which is its own cost lever.