GPT-5.5 for reasoning
GPT-5.5 is the #2 pick on LLMDex's llm for reasoning ranking out of 6 models we track for this use case. Below, the specific reasons it slots where it does, and when you should reach for an alternative.
Updated
At a glance
- Rank
- #2 of 6
- Context
- 400K tokens
- Output / 1M
- Pricing not published
- Released
- Mar 2026
Why GPT-5.5 fits this task
Three things about GPT-5.5 that map directly onto what this task rewards: Strong end-to-end agent performance across SWE-bench and GAIA. Beyond the task-specific fit, GPT-5.5 also brings industry-leading tool-use and function-calling reliability and wide ecosystem support, chatgpt, realtime api, responses api, both of which compound when the workload broadens.
The criteria this task rewards
LLMDex ranks best llm for reasoning on 5 criteria , these are the axes the ranking uses, in priority order:
- GPQA Diamond performance
- ARC-AGI public set scores
- Chain-of-thought coherence on novel puzzles
- Reasoning-token cost, expensive on flagship reasoning models
- Latency budget, reasoning runs are slow by design
How GPT-5.5 scores on each axis
Where GPT-5.5 costs you: pricing premium vs. open-weight alternatives. For most teams this is acceptable on this workload, the value of the strengths above outweighs the cost. For cost-bound workloads or teams with strict latency budgets, run an eval against the next two ranked models on real data before committing.
Strengths that pay off here
- Industry-leading tool-use and function-calling reliability
- Strong end-to-end agent performance across SWE-bench and GAIA
- Wide ecosystem support, ChatGPT, Realtime API, Responses API
- Polished multimodal grounding on screenshots and charts
Tracked weaknesses
- Pricing premium vs. open-weight alternatives
- Output cost climbs fast on agent loops with many reasoning tokens
- Stricter content policy than some peers for creative work
When to pick something else
If you can pay slightly more or accept slightly different tradeoffs, o3 from OpenAI ranks one position higher and tends to win on the hardest cases. OpenAI's flagship reasoning model, set the bar for hard math, GPQA, and agent benchmarks in 2025.
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Other models for reasoning
- o3 for reasoning
OpenAI's flagship reasoning model, set the bar for hard math, GPQA, and agent benchmarks in 2025.
Read guide - Claude Opus 4.7 for reasoning
Anthropic's mid-2026 flagship, ahead on SWE-bench, agent reliability, and writing quality.
Read guide - DeepSeek-R1 for reasoning
First open-weight reasoning model to match o1, the release that proved RL-from-scratch reasoning training was reproducible.
Read guide - Gemini 3 Pro for reasoning
Google's late-2025 flagship, set new benchmarks on long-context, vision, and reasoning at competitive pricing.
Read guide - o4 for reasoning
OpenAI's late-2025 standalone reasoning model, an evolution of o3 with deeper chain-of-thought and stronger multimodal reasoning.
Read guide
GPT-5.5 for other use cases
Direct comparisons
Frequently asked
Is GPT-5.5 good for reasoning?
GPT-5.5 is ranked #2 on LLMDex's reasoning list. OpenAI's mid-cycle GPT-5 refresh, improved reasoning, tool use, and multimodal grounding over the 2025 launch.How much does GPT-5.5 cost for reasoning?
OpenAI has not published per-token pricing for GPT-5.5 at the time of writing.What's a cheaper alternative to GPT-5.5 for reasoning?
The next ranked model on this task is Claude Opus 4.7. Compare both before committing.When should I NOT use GPT-5.5 for reasoning?
Tracked weakness: Pricing premium vs. open-weight alternatives. If that constraint is binding for your workload, the next-ranked model on this task is the safer pick.
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