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GPT OSS 20B vs Claude Fable 5

At a glance
OpenAIGPT OSS 20B

OpenAI's compact open-weights model for efficient inference.

131K ctx$0.03/$0.14 per M
AnthropicClaude Fable 5

Anthropic's Mythos-class flagship for ambitious, long-running professional work.

921M ctx$10.00/$50.00 per M#2/92
AI Output
All AI outputs

No captured outputs for these models yet.

Benchmarks
See rankings
OpenAIGPT OSS 20B
Reasoning
CodingInsufficient data
ReasoningInsufficient data
MathInsufficient data
Sources:Epoch AI·OpenRouter· as of 2026-07-10
Cheaper
Capability
Capability—
Reasoning & Knowledge
Factual Recall—
Math
Competition Math—
Agentic
Terminal Tasks3.4%
AnthropicClaude Fable 5
Reasoning
CodingInsufficient data
AgenticInsufficient data
ReasoningInsufficient data
Sources:Epoch ECI·Epoch AI·OpenRouter· as of 2026-07-10
Capability
CapabilityECI91.6
Reasoning & Knowledge
Factual Recall68.3%
Math
Competition Math99.7%
Agentic
Terminal Tasks—
Specs
OpenAIGPT OSS 20B
131K
Context
16K
Max output
Aug 2025
Released
AnthropicClaude Fable 5
1M
Context
128K
Max output
Jun 2026
Released
Capabilities
OpenAIGPT OSS 20B
Vision
Audio
Reasoning
AnthropicClaude Fable 5
Vision
Audio
Reasoning
Pricing
OpenAIGPT OSS 20B
Live pricing, shown before you run
Input$0.03/M tokens
Output$0.14/M tokens
AnthropicClaude Fable 5
Live pricing, shown before you run
Input$10.00/M tokens
Output$50.00/M tokens
Cache read$1.00/M tokens
Cache write$12.50/M tokens
Web search$0.01/search
Chat with GPT OSS 20BGo to model
Chat with Claude Fable 5Go to model
Frequently Asked Questions: GPT OSS 20B vs Claude Fable 5▼

Which is better, GPT OSS 20B or Claude Fable 5?

▼

Both GPT OSS 20B and Claude Fable 5 are capable AI models. The best choice depends on your specific use case: consider pricing, context window, speed, and which capabilities (vision, reasoning, audio) you need.

Which is cheaper, GPT OSS 20B or Claude Fable 5?

▼

GPT OSS 20B has a lower blended cost. GPT OSS 20B: $0.03 input / $0.14 output. Claude Fable 5: $10.00 input / $50.00 output.

Which has a larger context window, GPT OSS 20B or Claude Fable 5?

▼

Claude Fable 5 has a larger context window: GPT OSS 20B supports 131K tokens vs Claude Fable 5 at 1M tokens.

Do both GPT OSS 20B and Claude Fable 5 support vision?

▼

Claude Fable 5 supports vision/image input, but GPT OSS 20B does not.

What are the key differences between GPT OSS 20B and Claude Fable 5?

▼

Key differences: GPT OSS 20B is significantly cheaper; only Claude Fable 5 supports vision input. Compare full specs on this page.

Which model should I choose for my use case?

▼

If cost is your priority, choose the cheaper option. If you need the highest intelligence for complex tasks, pick the higher-scoring model. For long documents or codebases, choose the larger context window. You can try both GPT OSS 20B and Claude Fable 5 for free on idapt.app to see which performs better for your specific needs.

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