Best LLM for hard reasoning & debugging (2026)
When your daily-driver model gets stuck, you escalate. These are the highest-scoring models on SWE-bench Verified — the benchmark that best tracks real, gnarly bug-fixing.
🏆 Top pick: Gemini 3 Deep Think
Gemini 3 Deep Think tops the tracked SWE-bench scores at 80% — the model to reach for when a problem is genuinely hard.
The ranked list
| # | Model | SWE-bench | HumanEval | Input price | Context window |
|---|---|---|---|---|---|
| 1 | Gemini 3 Deep Think | 80% | 96% | $5 | 1M+ |
| 2 | MiMo V2.5 Pro | 79% | 76% | Free (self-hosted) | 1M+ |
| 3 | GPT-5.5 Pro | 78% | 96% | $30 | 1M+ |
| 4 | Doubao Seed 2.0 Pro | 77% | 93% | $0.47 | 256K |
| 5 | Doubao Seed 2.0 Code | 77% | 94% | $0.30 | 256K |
| 6 | GPT-5.1 Codex Max | 77% | 96% | $5 | 400K |
| 7 | Gemini 3 Pro | 76% | 95% | $2 | 1M+ |
| 8 | GPT-5.1 | 76% | 95% | $1.25 | 400K |
Why each made the list
1 Gemini 3 Deep Think
Hardest reasoning, research analysis, math olympiad and competitive programming
2 MiMo V2.5 Pro
Highest open-weight coding performance, 1M context agentic tasks, complex multi-step engineering, long-context reasoning
3 GPT-5.5 Pro
Hardest reasoning problems, math olympiad, research-grade analysis, mission-critical coding tasks where cost is no object
4 Doubao Seed 2.0 Pro
Cost-effective frontier coding, Codeforces-level competitive programming (3020 rating), AIME math (98.3%), production agentic workflows
5 Doubao Seed 2.0 Code
Cheapest frontier-class coding model on market, high-throughput code completion, CI-driven agent loops, bulk refactors at minimal cost
6 GPT-5.1 Codex Max
Multi-hour, cross-file engineering tasks where context compaction matters; enterprise Codex CLI use
7 Gemini 3 Pro
Long-horizon agentic tasks, generative UI, multi-modal reasoning, Antigravity-driven workflows
8 GPT-5.1
Default daily-driver coding agent with adaptive reasoning and warmer chat tone
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