GPT-6 Astra vs Fable 5.1: API costs
GPT-6 Astra and Claude Fable 5.1 both charge $10 per million input tokens and $50 per million output tokens at Standard rates. Fable 5.1 has cheaper cache reads. Astra also raises the price of the full request above 272K input tokens, so a large prompt can cost more than the base rates suggest.
These are direct API list prices in USD. The examples assume equal billable token counts; they do not measure equal quality, speed or cost per completed task.
Standard prices per million tokens
Checked against the OpenAI model page and Anthropic price list. Global/default processing, before taxes and extra tools.
| Token category | Astra ≤272K input | Astra >272K input | Fable 5.1, full context |
|---|---|---|---|
| Uncached input | $10 | $20 | $10 |
| Billable output | $50 | $75 | $50 |
| Cache reads | $1 | $2 | $0.25 |
| Cache writes (Astra / Fable 5-minute) | $12.5 | $25 | $12.5 |
| Fable 1-hour cache writes | Not this billing option | Not this billing option | $20 |
Use gpt-6-astra or claude-fable-5-1 when identifying the models. Claude Fable 5 is a separate version with $1 cache reads. Its price must not be substituted for the $0.25 Fable 5.1 rate. Astra has a 1.05M context window; Fable 5.1 has 1M. Both list a 128K maximum output.
Batch, Flex, Fast and charges outside the table
Eligible Batch work costs $5 input and $25 output per million on both models. Astra Flex also uses half of Standard rates; Astra Fast doubles the applicable rates. Its long-context multipliers still matter. The original 100K/10K example becomes $0.75 in Batch or Astra Flex, and $3 in Astra Fast. These modes have different availability and turnaround conditions.
Anthropic's published Fast price table does not list Fable 5.1. Do not copy an Opus Fast rate onto it. Contracted priority capacity and cloud-reseller bills need their own quote; this comparison uses direct, public token rates.
OpenAI lists a 10% uplift for eligible regional-processing endpoints on recent models. Claude US-only inference uses a 1.1× multiplier across token categories. Tools can add charges too: both providers list web search at $10 per 1,000 calls/searches, plus the applicable content-token cost. Check OpenAI's complete price list or Anthropic's linked table before adding search, storage or execution to your budget.
The same 100K input and 10K output budget
Assume one request uses 100,000 uncached input tokens and 10,000 billable output tokens, with no cache creation. Each model costs $1.5: $1 for input plus $0.50 for output. At 1,000 requests, either budget is $1,500.
Open both models with those exact inputs. The calculator starts with Standard, uncached pricing. Its cache toggle treats all entered input as reads from an existing cache; it does not estimate partial hits or cache writes. Use the worked example below for that breakdown.
A copied document can have different token counts under different tokenizers. Reasoning and thinking can also add billable output beyond the final answer you see. For a production estimate, replace these assumptions with each model's own usage totals and include unsuccessful attempts.
Count the first cache write before comparing hits
Suppose each request contains a reusable 90,000-token prefix, 10,000 fresh input tokens and 10,000 output tokens. Once that prefix is cached, an Astra call costs $0.69; Fable 5.1 costs $0.6225. The $0.0675 gap is 9.8% of this whole Astra request, even though Fable's cache-read unit price is 75% lower.
The first request must pay to create the cache. Treat write tokens as their own input category, not as an additional charge on the same tokens at the uncached rate. With one write followed by nine successful reads, the ten-call budget is:
| Cache option | First call | Each hit | 10 calls total |
|---|---|---|---|
| Astra, 30-minute lifetime | $1.725 | $0.69 | $7.935 |
| Fable, 5-minute lifetime | $1.725 | $0.6225 | $7.3275 |
| Fable, 1-hour lifetime | $2.4 | $0.6225 | $8.0025 |
Without caching, those ten calls cost $15. The table assumes every later call arrives while its cache is reusable and preserves the prefix. Rewrites or expired entries can require another write, so do not budget nine hits merely because nine calls repeat similar text.
OpenAI's caching guide gives GPT-5.6 and later a minimum 30-minute lifetime after a write or reuse, with a 1,024-token minimum prefix. Fable 5.1 uses a 512-token minimum and offers 5-minute or 1-hour writes; see Claude's caching rules. Lifetime is only one condition for a hit. Check actual cache-read and creation usage rather than assuming the discount applies.
The 272K boundary changes Astra's entire request
At exactly 272,000 uncached input and 10,000 output tokens, Astra costs $3.22. At 272,001 input, it costs $6.19002. The higher band applies to all input and cache tokens at 2× and all output at 1.5×, not just the extra token. Include cached input when counting the prompt.
At 300,000 uncached input and 10,000 output, Astra costs $6.75 and Fable 5.1 costs $3.5. Fable keeps Standard token rates throughout its 1M context. Reproduce the 300K example. Leave capacity for the answer: the advertised context window is not an unlimited input allowance.
API savings do not define subscription limits
In a Reddit discussion about Fable 5.1 caching, commenters disagreed about whether cheaper reads meant more subscription usage. The dollar-per-token arithmetic here describes API usage. It does not convert ChatGPT, Codex or Claude plan limits into a fixed token allowance.
For a model decision, record total API spend across the complete workflow and divide by accepted results. Include retries, tool calls and review time. A model that needs a longer answer or another attempt can erase the savings predicted by an equal-token example. This page does not rank their task quality or claim a measured speed advantage.
Continue with Astra's pricing page, the separate Fable 5.1 catalog entry, or the selected-model calculator. Model identity and limits are also documented in the official Fable 5.1 overview. AI API Prices editors checked these rates and calculations on October 10, 2026.