Claude Mythos 5vsgpt-oss-20b
Claude Mythos 5 | gpt-oss-20b | |
|---|---|---|
| Specifications | ||
ParametersA rough measure of how big the model is. More parameters usually means more capable and more expensive to run, though it is a poor guide on its own — a smaller, newer model often beats a larger, older one. | — | 21B |
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 | ||
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. | — | $0.03CoreWeave |
Cheapest outputLowest output rate across third-party providers, excluding the lab itself. May come from a different provider than the cheapest input. | — | $0.13CoreWeave |
| Benchmarks | ||
SWE-Bench VerifiedCoding — Real coding tasks pulled from open-source projects — the AI has to find and fix actual bugs. A human-checked version of the original SWE-Bench. Higher is better. | 95.5% | 60.7% |
Humanity's Last Exam · with toolsMultidisciplinary reasoning — Humanity's Last Exam — extremely hard expert questions across many subjects. “With tools” means the AI is allowed to search the web or run code while answering. Higher is better. | 64.5% | 17.3% |
| BenchmarksPublished by one model only | ||
Terminal-Bench 2.1Agentic terminal coding — Can the AI work in a command-line terminal — running commands and finishing technical setup tasks the way a developer would? Higher is better. | 88% | — |
BrowseCompWeb browsing — Can the AI browse the web and track down hard-to-find answers? Higher is better. | 88% | — |
Humanity's Last Exam · no toolsMultidisciplinary reasoning — Humanity's Last Exam — extremely hard expert questions across many subjects, written so you can't just look up the answer. “No tools” means the AI answers on its own. Higher is better. | — | 10.9% |
GPQA DiamondScience — Graduate-level science questions in biology, physics, and chemistry — hard enough that subject-matter PhDs score around 65%. Higher is better. | — | 71.5% |
MMLUGeneral knowledge — A 57-subject multiple-choice exam — history, law, medicine, maths — that was the standard measure of how much a model knows from 2020 until roughly 2024, when frontier scores crowded into the high 80s and labs moved on to harder tests. The scores here were published years apart under different testing setups, so read them as a historical record rather than a like-for-like ranking. Higher is better. | — | 85.3% |
OSWorld-VerifiedAgentic computer use — Can the AI actually operate a computer — clicking, typing, and using real apps — to finish tasks on its own? Higher is better. | 85% | — |
| Overview | ||
| Company | Anthropic | OpenAI |
| Release date | Jun 9 2026 | Aug 5 2025 |
| Access | Proprietary | Open Weight |
Other comparisons
Frequently asked questions
Claude Mythos 5 leads gpt-oss-20b on 2 of the 2 benchmarks they both report (SWE-Bench Verified, Humanity's Last Exam). gpt-oss-20b shipped 308 days before Claude Mythos 5, so benchmark comparisons should account for the intervening progress.
Context windows are 1M (Claude Mythos 5) vs 128k (gpt-oss-20b). Claude Mythos 5 is proprietary, while gpt-oss-20b is open weight.
On SWE-Bench Verified, Claude Mythos 5 leads at 95.5% vs gpt-oss-20b at 60.7%. On Humanity's Last Exam · with tools, Claude Mythos 5 leads at 64.5% vs gpt-oss-20b at 17.3%.
Claude Mythos 5 was released by Anthropic on Jun 9 2026.
gpt-oss-20b was released by OpenAI on Aug 5 2025.
Claude Mythos 5 leads on SWE-Bench Verified — Claude Mythos 5 95.5% vs gpt-oss-20b 60.7%.
Claude Mythos 5 leads on Humanity's Last Exam · with tools — Claude Mythos 5 64.5% vs gpt-oss-20b 17.3%.
Claude Mythos 5 has a 1M context window; gpt-oss-20b has 128k.
Claude Mythos 5 is a proprietary model released by Anthropic. gpt-oss-20b is an open weight model released by OpenAI.