Head-to-head
GPT-5.5 vs Claude Sonnet 5: which AI model wins in 2026?
GPT-5.5 ($30/1M out) and Claude Sonnet 5 ($15/1M out ($10 intro until 2026-08-31)) are two of the most-used AI models in 2026. Across 6 community votes, GPT-5.5 leads with 57% approval.
Quick verdict
On Reasoning, pick GPT-5.5: the arena rates it 5/5 against 4.5/5 for Claude Sonnet 5. On budget, Claude Sonnet 5 wins: it starts at $15/1M out ($10 intro until 2026-08-31) versus $30/1M out for GPT-5.5.
Line-by-line comparison
Strengths and weaknesses
GPT-5.5
- 1M-token context window (1,050,000) with 128K max output and reasoning effort tunable from none to xhigh
- State-of-the-art ARC-AGI-2 at 85.0% (vs 73.3% for GPT-5.4) and Terminal-Bench 2.0 at 82.7%
- Strong agentic coding autonomy: devs report it one-shots tasks that took GPT-5.4 multiple turns and fixes its own mistakes; +50 points on Code Arena vs GPT-5.4
- Aggressive discounts: 90% off cached input ($0.50/1M) and 50% off via Batch or Flex ($2.50/$15)
- Fast for a frontier reasoner: devs say it is the first GPT model comfortable to run at medium or low thinking effort
- List price doubled vs GPT-5.4 ($5/$30 vs $2.50/$15) for the same 1M-token context window
- Overly literal instruction-following: devs report it fails to infer intent in obvious places where Claude succeeds
- Trails Claude Opus 4.8 on SWE-bench Pro (58.6% vs 69.2%); HN developers still favor Claude roughly 2:1 for coding
- Sometimes too conservative with code changes or skips deep reasoning entirely, answering immediately on complex prompts
- Long-context surcharge: prompts over 272K input tokens are billed 2x input and 1.5x output for the whole session
Claude Sonnet 5
- Large agentic gains over Sonnet 4.6: Terminal-Bench 2.1 80.4% vs 67.0%, OSWorld-Verified 81.2% vs 78.5%, SWE-bench Pro 63.2% vs 58.1%
- Matches Opus 4.8 on knowledge work (GDPval-AA v2: 1,618 vs 1,615) and nearly ties it on Humanity's Last Exam with tools (57.4% vs 57.9%) at 60% of Opus 4.8 pricing (40% during the intro window)
- 1M token context window and 128K max output; introductory pricing of $2/$10 per 1M tokens through Aug 31, 2026
- Persistent self-verifying agent behavior: hands-on reviews note it tests its own code and iterates on hard problems until solved, unlike Sonnet 4.6
- First Sonnet with xhigh effort level and high-resolution vision (2576px images); adaptive thinking enabled by default
- Higher code-review precision than Sonnet 4.6 (38-40% vs 29%), producing fewer false-positive findings
- New tokenizer inflates token counts roughly 30% for the same text (1.0-1.35x per Anthropic; ~1.4x English, ~1.28x Python measured by Simon Willison), raising effective cost despite the unchanged sticker price
- Verbose and token-hungry: ~$2.29 per task vs ~$1.20 for Sonnet 4.6 in independent tests (ranked 101st of 161 for cost efficiency); at high effort cost-per-task can exceed Opus 4.8
- Measurably slower than Sonnet 4.6 on small routine edits and prone to over-engineering simple tasks (CodeRabbit hands-on review)
- Sampling parameters (temperature, top_p, top_k) removed; non-default values return a 400 error, breaking existing pipelines
- Launch sentiment on HN/Reddit was mixed: the '5' label was seen as overpromising, and stricter cybersecurity safeguards can refuse benign security-adjacent work
Cast your verdict
One recommendation per tool per gladiator. It reshapes the crowd score everyone sees.
The arena’s verdict on GPT-5.5
Pick GPT-5.5 over GPT-5.4 if you need stronger agentic autonomy, terminal-heavy workflows, or SOTA abstract reasoning, but know the list price doubled from GPT-5.4's $2.50/$15 to $5/$30 while the 1M-token context stayed the same. Teams doing high-stakes multi-file refactoring may still prefer Claude Opus, which leads SWE-bench Pro (69.2% vs 58.6%) and infers intent better from loose prompts. Budget-sensitive users should mind the 272K-token surcharge and reports of faster limit burn, and lean on caching, Batch, or Flex to halve costs.
The arena’s verdict on Claude Sonnet 5
Choose Sonnet 5 if you run coding, terminal or computer-use agents and want near Opus 4.8 quality at Sonnet prices, especially during the $2/$10 intro window; it is a strict upgrade over Sonnet 4.6 at low and medium effort. Budget for the new tokenizer and its verbosity: real per-task costs run well above Sonnet 4.6, and at the highest effort levels Opus 4.8 can be the better deal per solved task. Avoid it for latency-sensitive small edits or pipelines that rely on temperature and top_p, which now error. Sonnet 4.6 remains the pragmatic pick for high-volume tiny-diff workloads.
What the crowd says
On GPT-5.5
“It is painfully literal. Where Claude infers intent in obvious places, 5.5 wants everything spelled out. And the price doubled vs 5.4 for the same 1M context.”
“85 on ARC-AGI-2 and you can feel it. Stuff that used to stall my agent just resolves now. 1M context with 128K output covers every workflow I have.”
“5.5 one-shots tasks that took 5.4 three turns, and it fixes its own mistakes mid-run instead of doubling down. The reasoning effort dial from none to xhigh is genuinely useful.”
On Claude Sonnet 5
“Cheap per token, pricey per task. Independent tests had it near $2.29 a task vs $1.20 on 4.6, and at high effort it can out-cost Opus 4.8. It will not stop talking.”
“Terminal-Bench going 67 to 80 over Sonnet 4.6 matches what I see. My CI-fix agent went from constant babysitting to mostly hands-off overnight.”
“Matches Opus 4.8 on knowledge work at 60% of the price, and the intro $2/$10 window makes it silly value. My research agent runs on Sonnet 5 now, zero regrets.”
Keep comparing
Frequently asked questions
Is GPT-5.5 better than Claude Sonnet 5?
On Reasoning, GPT-5.5 rates higher (5/5 vs 4.5/5). The right pick depends on your use case. The line-by-line comparison on this page breaks down pricing, key specs and arena ratings.
Which is cheaper, GPT-5.5 or Claude Sonnet 5?
Claude Sonnet 5 is cheaper: it starts at $15/1M out ($10 intro until 2026-08-31), while GPT-5.5 starts at $30/1M out.
How much do GPT-5.5 and Claude Sonnet 5 cost per 1M tokens?
GPT-5.5: $5/1M in per 1M input tokens, $30/1M out per 1M output tokens. Claude Sonnet 5: $3/1M in ($2 intro until 2026-08-31) per 1M input tokens, $15/1M out ($10 intro until 2026-08-31) per 1M output tokens.