Anthropic's upgraded Mythos-class flagship, with the biggest gains in agentic coding, long-running agentic workflows, and knowledge work.
OpenAI's most advanced agentic coding model with 400K context.
No shared demos for these models yet.
No captured outputs for these models yet.
Both Claude Fable 5.1 and GPT 5.3 Codex 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.
GPT 5.3 Codex has a lower blended cost. Claude Fable 5.1: $10.00 input / $50.00 output. GPT 5.3 Codex: $1.75 input / $14.00 output.
Claude Fable 5.1 has a larger context window: Claude Fable 5.1 supports 1M tokens vs GPT 5.3 Codex at 400K tokens.
Yes, both Claude Fable 5.1 and GPT 5.3 Codex support vision/image input.
Key differences: GPT 5.3 Codex is significantly cheaper. Compare full specs on this page.
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 Claude Fable 5.1 and GPT 5.3 Codex for free on idapt.app to see which performs better for your specific needs.