Model comparison
Claude Fable 5.1 vs GPT-6 Sol: a steady 5x price gap
Claude Fable 5.1 costs 5x what GPT-6 Sol does per token, and caching leaves that ratio intact. How Anthropic's top model compares with OpenAI's middle one.
· Prices as of September 28, 2026
Claude Fable 5.1
Anthropic · Released September 1, 2026
Anthropic's most capable generally available model, aimed at demanding reasoning and long-horizon agentic coding. Anthropic suggests it when Opus-tier results fall short.
Claude Fable 5.1 facts and comparisonsGPT-6 Sol
OpenAI · Released September 22, 2026
The mid-priced GPT-6 model, which OpenAI pitches for complex coding and agent workflows and which the Codex docs recommend for complex coding.
GPT-6 Sol facts and comparisons
The short answer
GPT-6 Sol costs a fifth as much as Claude Fable 5.1 on every list price, and the example agentic coding session keeps the 5x ratio: $2.10 against $10.50. Fable 5.1 is Anthropic's most capable generally available model, which Anthropic suggests when Opus-tier results fall short, while GPT-6 Sol is OpenAI's mid-priced GPT-6 model and the Codex docs' pick for complex coding. Use Sol for everyday volume in Codex, and keep Fable 5.1 for work where cheaper models have fallen short.
Choose Claude Fable 5.1 if
- Anthropic's own guidance applies: results from Opus-tier models fall short on the task at hand.
- You work in Claude Code, where /model fable selects it.
- Your prompts pass 272K input tokens, where GPT-6 Sol switches to long-context rates and Fable 5.1 stays at standard rates across its 1M window.
- Your long runs lean on the cache: a Fable 5.1 hit costs $0.25 per million, only 1.3x Sol's $0.20 despite the 5x input price.
Choose GPT-6 Sol if
- You want the lower price: $2 input and $10 output per million tokens, 80% less than Fable 5.1.
- You work in Codex, whose docs recommend GPT-6 Sol for complex coding and suggest it to users of GPT-5.6 Sol, GPT-5.6 Terra, and GPT-5.4.
- You run agent sessions all day: at 110 a month, the example session costs $924.00 less on Sol than on Fable 5.1.
Side by side
Specs and prices
| Fact | Claude Fable 5.1 | GPT-6 Sol |
|---|---|---|
| Maker | Anthropic | OpenAI |
| API model id | claude-fable-5-1 | gpt-6-sol |
| Released | September 1, 2026 | September 22, 2026 |
| Status | Current | Current |
| Context window | 1M tokens | 1.05M tokens |
| Max output | 128K tokens | 128K tokens |
| Open weights | No | No |
| Input, per 1M tokens | $10 | $2 |
| Cache hit, per 1M | $0.25 | $0.20 |
| Cache write, per 1M | $12.50 (5-minute), $20 (1-hour) | $2.50 |
| Output, per 1M tokens | $50 | $10 |
| Runs in | Claude Code, Cursor, OpenCode, OpenRouter, and GitHub Copilot | Codex, OpenCode, OpenRouter, and GitHub Copilot |
Standard API rates in US dollars, as published by each maker (Claude Fable 5.1: September 26, 2026; GPT-6 Sol: September 28, 2026). Batch and priority tiers, taxes, and subscription plans are not included. Claude Fable 5.1: The full 1M context window is billed at standard rates. GPT-6 Sol: Requests over 272K input tokens cost 2x for input and cache and 1.5x for output, for the whole request.
Cost
What the same work costs
The same token counts, priced at each model’s published rates. Cached tokens are billed at each maker’s cache prices, so the session shows what caching is worth on each model.
Real sessions differ: the two models count the same code as different numbers of tokens, and reasoning settings change how much each one writes. Your own history is the real test.
| Workload | Claude Fable 5.1 | GPT-6 Sol |
|---|---|---|
| Agentic coding session, 100K input, 400K written to cache, 2M read from cache, 50K output | $10.50 | $2.10 |
| Large one-off review, 150K input with no cache hits, 10K output | $2.00 | $0.40 |
| Output-heavy generation, 30K input, 80K output | $4.30 | $0.86 |
| A month of sessions, 110 sessions: 5 a day, 22 working days | $1,155.00 | $231.00 |
| Where the session’s cost goes | ||
| Cache writes | $6.50 | $1.00 |
| Cache reads | $0.50 | $0.40 |
| Uncached input | $1.00 | $0.20 |
| Output | $2.50 | $0.50 |
- caching saves on the session with Claude Fable 5.1 (62%)
- $17.00
- caching saves on the session with GPT-6 Sol (62%)
- $3.40
Does caching narrow the 5x gap?
It would be natural to expect it to. Anthropic prices a Claude Fable 5.1 cache hit at 0.025x input, a 97.5% discount, while OpenAI's discount on GPT-6 Sol is 90%. Per cached token read, Fable 5.1 charges $0.25 per million and Sol $0.20, so the read gap is 1.3x instead of 5x.
The writes pull the other way. The session writes 200K tokens to a 5-minute cache and 200K to a 1-hour cache, and Anthropic charges 2x input for the 1-hour kind, $20 per million on Fable 5.1. OpenAI charges Sol a flat 1.25x, $2.50. Cache writes come to $6.50 of Fable 5.1's $10.50 session, 62% of it, against $1.00 and 48% on Sol.
The deeper read discount and the heavier write premium offset each other, so all three workloads keep the 5x ratio: $2.00 against $0.40 for the uncached review and $4.30 against $0.86 for output-heavy generation. Over 110 sessions a month the example comes to $1,155.00 on Fable 5.1 and $231.00 on Sol.
Anthropic's top tier against OpenAI's middle tier
These models sit on different rungs of their makers' lines. Anthropic counts Fable 5.1 among "the world's most advanced models for coding and knowledge work" and names long-running agentic coding and multistep research among its strengths. It points most work to Claude Opus 5.5 first and suggests Fable 5.1 when Opus-tier results fall short.
OpenAI's GPT-6 line runs from GPT-6 Luna, the cheapest, through GPT-6 Sol to GPT-6 Astra, the most capable and most expensive. OpenAI says Sol is "Built to power complex coding and agentic workflows," and the Codex docs recommend it for complex coding. The price-matched rival for Fable 5.1 would be Astra, which charges the same list rates.
So the practical question for most teams is whether their hardest tasks justify five times the cost. If those tasks are a small share of the work, sending only them to Fable 5.1 keeps the average close to the lower price. Each model keeps its own cache, so switching mid-task starts caching over.
Context, effort, and token counts
Both models take about a million tokens of context: 1M on Fable 5.1 and 1.05M on Sol, which accepts up to 922K of it as input. Above 272K input tokens, OpenAI bills a Sol request at 2x for input and cache and 1.5x for output, for the whole request. Anthropic bills Fable 5.1's full window at standard rates. Each writes up to 128K tokens per response.
Default effort differs: high for Fable 5.1, and medium for Sol in both the API and Codex. Effort changes how many output tokens each model writes, so the 5x output price gap can grow or shrink with settings. Fable 5.1 also uses Anthropic's newer tokenizer, which counts about 30% more tokens than earlier Claude models for the same text, so identical prompts do not produce identical token counts at the two makers.
Prompt caching
How each maker bills cached tokens
Anthropic
Claude caches a prompt prefix up to a breakpoint. One top-level cache_control field places the breakpoint automatically and moves it as the conversation grows, or you can mark up to 4 blocks yourself. Claude Code manages caching for you.
A 5-minute cache write costs 1.25x the input price and a 1-hour write costs 2x. A cache hit costs 0.1x input on most models, 0.05x on Claude Opus 5.5, and 0.025x on Claude Fable 5.1 and Claude Mythos 5.1. Every hit restarts the cache lifetime at no charge.
Anthropic's rule of thumb: a 5-minute write pays for itself after one cache read, and a 1-hour write after two.
In Claude Code, the main conversation uses the 1-hour cache on a Claude subscription and the 5-minute cache with an API key. Each model has its own cache, so switching models starts over.
Source: Anthropic: Prompt caching
OpenAI
Prompt caching is on by default. From GPT-5.6 on you can also mark up to four explicit cache breakpoints, while GPT-5.5 and earlier cache automatically only.
From GPT-5.6 on, a cache write costs 1.25x the uncached input price and a cache hit costs 0.1x. GPT-5.5 and earlier add no charge for writing the cache: written tokens are billed as ordinary input, and a hit costs 0.1x on the models compared here.
On GPT-5.6 and later, a cached prefix stays reusable for at least 30 minutes after its last use, and caching starts at 1,024 input tokens.
Source: OpenAI: Prompt caching
Your own numbers
See what Claude Fable 5.1 and GPT-6 Sol really cost you.
everyaitoken reads your Claude Code, Cursor, OpenCode, OpenRouter, and Codex history on your Mac and prices every request at API rates, with what caching saved or cost. $9 once.
FAQ
Questions
How much more does Claude Fable 5.1 cost than GPT-6 Sol?
Five times as much on every list price: $10 against $2 for input and $50 against $10 for output. The example agentic session costs $10.50 on Fable 5.1 and $2.10 on Sol, a difference of $8.40, and at 110 sessions a month the gap reaches $924.00. These are API-equivalent estimates, and subscription plans are priced differently.
Is GPT-6 Sol OpenAI's most capable model?
No. OpenAI gives that title to GPT-6 Astra, which is also its most expensive GPT-6 model. Sol is the mid-priced tier, which OpenAI built for complex coding and agentic workflows and which the Codex docs recommend for complex coding.
Where can I use each model?
Fable 5.1 runs in Claude Code, Cursor, OpenCode, OpenRouter, and GitHub Copilot. GPT-6 Sol runs in Codex, OpenCode, OpenRouter, and GitHub Copilot. Fable 5.1 is never Claude Code's default model, so you switch to it with /model fable.
How can I tell whether Fable 5.1 is worth it for my team?
Compare what your hardest tasks actually cost on each model rather than relying on list prices. EveryToken reads local Claude Code and Codex history on a Mac, prices every request at API rates, and splits the cost by model, with what caching saved or cost.
Sources
- Anthropic: Pricing
- Anthropic docs: Claude Fable 5.1
- Anthropic: Claude Fable 5.1 and Claude Mythos 5.1
- Claude Code docs: Model configuration
- Cursor docs: Claude Fable 5.1
- OpenRouter: Claude Fable 5.1
- OpenCode docs: Zen
- GitHub Docs: Supported AI models in Copilot
- OpenAI: API pricing
- OpenAI docs: GPT-6 Sol
- OpenAI: Introducing GPT-6 Sol and Luna
- OpenAI: API changelog
- Codex docs: Models
- OpenRouter: GPT-6 Sol
- Anthropic: Prompt caching
- OpenAI: Prompt caching