Grok 4.5 First Impressions: Opus-Level Output vs Fable

Melvin Vivas · X post · 2026-07-09 · Open on X

Topics: Industry Trends & Job Market, LLM Fundamentals, AI Dev Tools & Productivity · Level: beginner

Summary

The creator compared the newly released Grok 4.5 with Fable on the same tasks and found the outputs comparable. He calls it 'Opus level'. The quoted announcement says Grok 4.5 was trained in partnership with SpaceXAI and is the first model they built for more than software engineering.

Key points

• Grok 4.5 was released and the creator rates it as 'Opus level' for coding.
• Side-by-side test against Fable gave comparable output.
• He plans to use it in Cursor for complex projects.
• The quoted announcement says it was trained with SpaceXAI and built for more than software engineering.
• Tip: when a new model drops, compare it side by side with your current model on your own tasks before switching.

Resources mentioned

• Grok 4.5 · tool · x.ai · paid
  An LLM said to be trained in partnership with SpaceXAI, pitched as a general model beyond software engineering.
  Also in: Grok 4.5 Works Well as the Model Behind Hermes Agent (Melvin Vivas on X · notes), Models That Work With the Hermes Agent for Personal Productivity (Melvin Vivas on X · notes), Agent-Made Video in 10 Minutes: Hermes Agent + Grok 4.5 + Hyperframes (Melvin Vivas on X · notes), Personal Assistant Agent on Hermes: Morning Briefings and Inbox Triage (Melvin Vivas on X · notes) and 9 more
• Fable · tool · anthropic.com · paid
  Named as what the creator used with Devin for this build; the post gives no details about what it is.
  Also in: Demo: One-Shotting a Flappy Bird iPhone App with Devin and Fable 5.1 (Melvin Vivas on X · notes), Subagents with mixed models: a strong planner and a fast executor (Melvin Vivas on X · notes), Cognition's SWE-2 Coding Model Now in Devin (Melvin Vivas on X · notes), GPT-6 Astra Access Across Plans vs Fable on Claude Max (Melvin Vivas on X · notes) and 10 more
• Cursor · tool · x.com · free · recommended by both Bashiri Smith & Melvin Vivas
  AI-native code editor (VS Code with AI built in).
  Also in: GLM 5.3 and GLM 5.3 Flash now in Cursor (Melvin Vivas on X · notes), Grok Bot Can Now Hand Off Coding Tasks to Cursor (Melvin Vivas on X · notes), Why Plan Mode Still Matters in AI Coding Assistants (Codex, Claude, Cursor) (Melvin Vivas on X · notes), Why Plan Mode Still Matters in AI Coding Agents (Codex, Claude, Cursor) (Melvin Vivas on X · notes) and 121 more

Try this

• Test a new model side by side against your current one on real tasks before adopting it.