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Fable 5 dominates benchmarks: 78% on ExploitBench versus GPT55’s 34%, 66% on HealthBench versus GPT55’s 51.8%, 13.3% on the legal agent benchmark versus GPT55’s 2.1%, and 1932 on GDP Val’s knowledge work test versus Opus 48’s 1890.
The model excels at agentic coding: 80.3% on Swebench Pro versus GPT55’s 58.6%, 88% on Terminal Bench versus GPT55’s 83.4%, and 29.3% on Frontier Code versus Opus 48’s 13.4%. Fable scored 91% on Every’s Senior Engineer benchmark.
Artificial Analysis found Fable 5 topped its blended benchmark run, overtaking Opus 48 and GPT55, though some noted the overall gap was only five points.
API pricing for Fable 5 is $10 per million input tokens and $50 per million output tokens, double Opus’s cost but lower than some expected. Mythos preview within Project Glasswing costs more than double.
Fable 5 has strict guardrails, automatically routing queries about cybersecurity, biology, chemistry, or distillation to Opus 48. Anthropic says 95% of sessions don’t trigger a fallback but is 'hardcore' about biology/chemistry filters.
Users report Fable flags basic biology terms like 'mitochondria' and 'cancer' as biosecurity risks, switching to Opus 48. Creo, Daria Anupmas, and Fernando documented these blocks.
Hill argues frontier models like Anthropic's Opus 4.8 and OpenAI's unreleased Fable 5 are heavily subsidized, creating a dangerous dependency akin to a drug dealer giving cheap drugs.
Hill asserts benchmarks are misleading for AI model quality; real competence must be felt through hands-on use, especially in programming where Opus 4.8 leads and Fable 5 represented a major jump.
Gemini 3.5 Flash benchmarks show competent but not state-of-the-art performance against Opus 4.7 and GPT-5.5, with its high token inefficiency making its speed focus questionable given the enterprise's primary cost concerns.
On the Artificial Analysis Coding Agent Index, GPT-5.6 Sol was a close second to Fable 5 but completed the run at a third of Fable's cost and was 40% cheaper than Opus 4.
Nathaniel Whittemore reports Meta's Muse Spark 1.1 benchmarks show competitive performance with Opus 4.8 and GPT-5.5, with strengths in personal agentic tasks and significant cost advantages.
Chubby notes Muse Spark 1.1 is incredibly affordable, costing $0.92 on VibeCodebench versus $5.09 for Opus 4.8 and $12.51 for Fable 5. Rayan from Vals.ai states it's one-tenth the cost of both Fable and GPT-5.5.