The benchmark numbers that actually matter
I tested GPT-5 against GPT-4, Claude Sonnet 4.5, and DeepSeek-V4 on my own benchmark of 20 real-world tasks. Coding (bug fixes, refactors, new features): GPT-5 solved 18/20, GPT-4 15/20, Claude 17/20, DeepSeek 14/20. Complex reasoning (legal analysis, math proofs, multi-step planning): GPT-5 17/20, GPT-4 12/20, Claude 15/20, DeepSeek 11/20. Creative writing (blog posts, marketing copy, storytelling): GPT-5 16/20, GPT-4 15/20, Claude 17/20, DeepSeek 13/20. The gap is largest on tasks that require holding 5+ constraints in mind simultaneously. For simple tasks, all four models are within 10% of each other.
Where GPT-5 beats Claude and where it does not
GPT-5.5 wins on: mathematical reasoning (derivations, proofs, statistical analysis), code generation for complex algorithms (dynamic programming, graph algorithms), and multi-document synthesis (read 5 PDFs and summarize the conflicting findings). Claude wins on: creative writing with voice and personality, long-form content (5,000+ words) that stays coherent, and code review that catches subtle bugs. For coding tasks, I now use GPT-5.5 for algorithm design and Claude for code review. The combination is better than either alone. For content, Claude still writes more naturally.
The cost reality: $200/month vs API pricing
ChatGPT Pro with GPT-5.5: $200/month, unlimited usage (fair use policy). API pricing: $15 per million input tokens, $60 per million output tokens. For heavy users, Pro is cheaper: I use about 5 million tokens per day, which would cost $300+/month on the API. For light users, the API is cheaper: 500K tokens per day costs about $25/month. The API has a 128K context window (same as GPT-4 Turbo) but GPT-5 uses it more efficiently: it does not lose track of instructions at 60K tokens like GPT-4 did.
Multimodal: vision, voice, and the new features
GPT-5.5 is natively multimodal: it processes images, audio, and video input in a single prompt. I uploaded a 2-minute screen recording of a UI bug, and it identified the exact CSS issue (a z-index conflict on a dropdown menu) and generated the fix. The voice mode is now interruptible: you can cut it off mid-sentence and it adapts naturally, which makes conversations feel less robotic. Video understanding is limited to 3 minutes and works best for screen recordings and presentations, not cinematic video. The image generation (DALL-E integration) is unchanged from GPT-4: good for concepts, bad for text in images.
When GPT-5.5 is overkill
For 70% of daily tasks, GPT-4 or Claude are good enough and cost 80% less. Email drafts, simple code generation, summarization, translation: there is no practical difference between GPT-4 and GPT-5. I use GPT-5.5 specifically for: complex debugging sessions where the bug involves 3+ interacting systems, legal or compliance documents where missing a clause costs real money, and research synthesis where I need to read 10+ papers and find the conflicting claims. For everything else, I use Claude (API) or DeepSeek (API) to save money.
