Claude Mythos 5.1vsGPT-4o
Claude Mythos 5.1 | GPT-4o | |
|---|---|---|
| Specifications | ||
Context windowHow much text the model can hold in mind at once — your question, any documents you attach, the conversation so far, and its own reply. Go past it and the earliest part falls out of view. | 1M | 128k |
| API pricingUSD per 1M tokens · lower wins | ||
Input priceWhat you pay for everything you send the model — your question, plus any documents or earlier conversation you include with it. | — | $2.50 |
Output priceWhat you pay for the text the model writes back. It is normally the dearer half: producing an answer costs more than reading one. | — | $10.00 |
Cached input priceA reduced rate for text you send over and over. If every request starts with the same instructions or the same document, the provider keeps a copy ready and charges less to read it again. | — | $1.25 |
Cheapest inputLowest input rate across third-party providers, excluding the lab itself. The cheapest endpoint may run a quantised build or a shorter context — see "Available from" on the model page. | — | $2.50Azure |
Cheapest outputLowest output rate across third-party providers, excluding the lab itself. May come from a different provider than the cheapest input. | — | $10.00Azure |
| BenchmarksPublished by one model only | ||
BullshitBench v2Nonsense detection — Given a confidently-worded but nonsensical prompt, does the AI spot that it makes no sense and push back — instead of playing along and inventing an answer? The score is how often it clearly called out the nonsense. Higher is better. | — | 12% |
Terminal-Bench 4.0Agentic terminal coding — Can the AI work in a command-line terminal — running commands and finishing technical setup tasks the way a developer would? Version 4.0 recalibrated how much time, CPU and memory each task gets, removed eight tasks and fixed nineteen, so fewer runs fail for reasons that have nothing to do with the model. Scores are not comparable with earlier versions. Higher is better. | 60.9% | — |
GPQA DiamondScience — Graduate-level science questions in biology, physics, and chemistry — hard enough that subject-matter PhDs score around 65%. Higher is better. | — | 49.9% |
| Overview | ||
| Company | Anthropic | OpenAI |
| Release date | Sep 1 2026 | May 13 2024 |
| Access | Proprietary | Proprietary |
Other comparisons
Frequently asked questions
Claude Mythos 5.1 and GPT-4o don't publish scores on any of the same benchmarks, so there's no direct head-to-head comparison. Only GPT-4o has a verified first-party API price: $2.50 per million input tokens and $10.00 per million output tokens. No pay-as-you-go API rate is tracked for Claude Mythos 5.1. GPT-4o shipped 841 days before Claude Mythos 5.1, so benchmark comparisons should account for the intervening progress.
Context windows are 1M (Claude Mythos 5.1) vs 128k (GPT-4o).
Direct benchmark comparisons are unavailable — Claude Mythos 5.1 and GPT-4o don't publish scores on any of the same benchmarks.
Claude Mythos 5.1 was released by Anthropic on Sep 1 2026.
GPT-4o was released by OpenAI on May 13 2024.
Only GPT-4o has a verified first-party API price: $2.50 per million input tokens and $10.00 per million output tokens. No pay-as-you-go API rate is tracked for Claude Mythos 5.1. Rates are pay-as-you-go API prices verified on August 18, 2026.
Claude Mythos 5.1 has a 1M context window; GPT-4o has 128k.