GPT-5.6 Sol Pro vs Grok 4.20
Grok 4.20 costs 8.0x less per output token than GPT-5.6 Sol Pro ($2.50 vs $20.00 per million). Updated October 21, 2026; 3 benchmarks have a result for both.
GPT-5.6 Sol Pro or Grok 4.20: which to pick
Only Grok 4.20 has a coding score, 33.3 on the Vibe Coding Index; GPT-5.6 Sol Pro has none, so the two cannot be ranked on coding.
Pick GPT-5.6 Sol Pro for work measured by WeirdML or DTBench, where it leads.
- Shared results
- 3
- GPT-5.6 Sol Pro only
- 4
- Grok 4.20 only
- 52
- Like-for-like categories
- 2 of 9
Only benchmarks that tested both models count toward a pick; a result only one model has is shown but not compared.
Which one for your work
Each card is decided by one number both models carry. Where only one has it, the card says so and makes no call.
Coding
Vibe Coding Index, six public coding benchmarks
No call
Only Grok 4.20 has a coding score, so no call is made.
One side not measured
Intelligence
AA Intelligence Index
No call
Only Grok 4.20 has a AA Intelligence Index result, 25.7.
Directional only
Reasoning
GPQA Diamond
No call
Only Grok 4.20 has a GPQA Diamond result, 88.6%.
Directional only
Math
AIME
No call
Only Grok 4.20 has a AIME result, 96.5%.
Directional only
Knowledge
MMLU Pro
No call
Only Grok 4.20 has a MMLU Pro result, 86.3%.
Directional only
Web design
Design Arena: websites
No call
Only Grok 4.20 has a Design Arena: websites result, 1229.
Directional only
Long documents
Listed context window
Grok 4.20
Grok 4.20 takes 2M tokens against 1.05M.
Listed by OpenRouter
Everyday cost
1K input + 500 output tokens
Grok 4.20
GPT-5.6 Sol Pro $0.014, Grok 4.20 $0.0025 per turn.
List prices
Cost per solved task
One SWE-bench Verified task, solved
No call
Only Grok 4.20 has the number, $0.72.
Directional only
At a glance
- Coding index
- GPT-5.6 Sol Pro not benchmarked, Grok 4.20 33.3 from 2 benchmarks.
- Widest category
- Coding, 37.2 points apart on average over 1 shared benchmark.
- Widest single gap
- WeirdML: GPT-5.6 Sol Pro 89.4% against Grok 4.20 52.3%, 37.2 points apart on a 0 to 100 scale.
- Output price
- GPT-5.6 Sol Pro $20.00 against Grok 4.20 $2.50 per million output tokens, 8.0x apart.
- Context window
- GPT-5.6 Sol Pro takes 1.05M tokens, Grok 4.20 2M.
Benchmark by benchmark
First the score: boards each model leads, per category, where both have a result. Then every board, a category to a fold; bars are each result on a 0 to 100 scale, so compare the two in a row, not one row with another.
| Category | GPT-5.6 Sol Pro | Bars | Grok 4.20 | Ties |
|---|---|---|---|---|
| Coding | 1 | 0 | ||
| General | 2 | 0 | ||
| All shared boards | 3 | 0 |
CodingLike-for-likeSix of these boards feed the Vibe Coding Index10
| Benchmark | GPT-5.6 Sol Pro | Grok 4.20 | Leader |
|---|---|---|---|
| LiveCodeBench (Vals AI) | Not measured | 84.3% | Only Grok 4.20 measured |
| SWE-bench Verified (Vals AI) | Not measured | 72.2% | Only Grok 4.20 measured |
| Vibe Code Bench (Vals AI) | Not measured | 4.1% | Only Grok 4.20 measured |
| Code migration (Vals AI) | Not measured | 0.3% | Only Grok 4.20 measured |
| Terminal-Bench 2.1 (Vals AI) | Not measured | 44.2% | Only Grok 4.20 measured |
| Terminal-Bench Hard (Artificial Analysis run) | Not measured | 37.9% | Only Grok 4.20 measured |
| Terminal-Bench | Not measured | 57.3% | Only Grok 4.20 measured |
| WeirdML | 89.4% | 52.3% | GPT-5.6 Sol Pro |
| Neither model has a result on the other 31 boards here | |||
IntelligenceDirectional onlyPublic boards, shown as published, kept out of the index2 boards, none shared
| Benchmark | GPT-5.6 Sol Pro | Grok 4.20 | Leader |
|---|---|---|---|
| AA Intelligence Index | Not measured | 25.7 | Only Grok 4.20 measured |
| Epoch Capabilities Index | Not measured | 152.1 | Only Grok 4.20 measured |
Agentic workDirectional onlyPublic boards, shown as published, kept out of the index13 boards, none shared
| Benchmark | GPT-5.6 Sol Pro | Grok 4.20 | Leader |
|---|---|---|---|
| Design Arena: agents building web apps | Not measured | 1144 | Only Grok 4.20 measured |
| Design Arena: agents building full-stack apps | Not measured | 1054 | Only Grok 4.20 measured |
| Design Arena: agents building mobile apps | Not measured | 1090 | Only Grok 4.20 measured |
| Design Arena: agents building Android apps | Not measured | 1052 | Only Grok 4.20 measured |
| Design Arena: agents building Godot games | Not measured | 1089 | Only Grok 4.20 measured |
| Design Arena: HTML slides | Not measured | 1180 | Only Grok 4.20 measured |
| Finance Agent (Vals AI) | Not measured | 28.5% | Only Grok 4.20 measured |
| Tax Agent Bench (Vals AI) | Not measured | 7.0% | Only Grok 4.20 measured |
| Legal Research Bench (Vals AI) | Not measured | 13.9% | Only Grok 4.20 measured |
| Excel Modeling Benchmark (Vals AI) | Not measured | 11.7% | Only Grok 4.20 measured |
| τ²-Bench Telecom | Not measured | 93.0% | Only Grok 4.20 measured |
| APEX-Agents | 51.4% | Not measured | Only GPT-5.6 Sol Pro measured |
| Vending-Bench 2 | Not measured | $4,663 | Only Grok 4.20 measured |
| Neither model has a result on the other 28 boards here | |||
ReasoningDirectional onlyPublic boards, shown as published, kept out of the index9 boards, none shared
| Benchmark | GPT-5.6 Sol Pro | Grok 4.20 | Leader |
|---|---|---|---|
| GPQA Diamond | Not measured | 88.6% | Only Grok 4.20 measured |
| MMMU Pro (Vals AI) | Not measured | 83.5% | Only Grok 4.20 measured |
| GPQA Diamond (Artificial Analysis run) | Not measured | 91.1% | Only Grok 4.20 measured |
| Humanity's Last Exam (Artificial Analysis run) | Not measured | 34.5% | Only Grok 4.20 measured |
| ARC-AGI | Not measured | 89.5% | Only Grok 4.20 measured |
| ARC-AGI-2 | Not measured | 65.1% | Only Grok 4.20 measured |
| SimpleBench | 71.7% | Not measured | Only GPT-5.6 Sol Pro measured |
| Chess puzzles | 68.0% | Not measured | Only GPT-5.6 Sol Pro measured |
| Kagi LLM Benchmark | Not measured | 75.0% | Only Grok 4.20 measured |
| Neither model has a result on the other 13 boards here | |||
MathDirectional onlyPublic boards, shown as published, kept out of the index2 boards, none shared
| Benchmark | GPT-5.6 Sol Pro | Grok 4.20 | Leader |
|---|---|---|---|
| AIME | Not measured | 96.5% | Only Grok 4.20 measured |
| FrontierMath, tier 4 | 80.5% | Not measured | Only GPT-5.6 Sol Pro measured |
| Neither model has a result on the other 11 boards here | |||
KnowledgeDirectional onlyPublic boards, shown as published, kept out of the index8 boards, none shared
| Benchmark | GPT-5.6 Sol Pro | Grok 4.20 | Leader |
|---|---|---|---|
| MMLU Pro | Not measured | 86.3% | Only Grok 4.20 measured |
| LegalBench (Vals AI) | Not measured | 77.7% | Only Grok 4.20 measured |
| CaseLaw (Vals AI) | Not measured | 54.4% | Only Grok 4.20 measured |
| CorpFin (Vals AI) | Not measured | 63.7% | Only Grok 4.20 measured |
| TaxEval (Vals AI) | Not measured | 74.1% | Only Grok 4.20 measured |
| MortgageTax (Vals AI) | Not measured | 45.4% | Only Grok 4.20 measured |
| MedQA (Vals AI) | Not measured | 94.5% | Only Grok 4.20 measured |
| MedCode (Vals AI) | Not measured | 32.2% | Only Grok 4.20 measured |
| Neither model has a result on the other 10 boards here | |||
Web designDirectional onlyPublic boards, shown as published, kept out of the index8 boards, none shared
| Benchmark | GPT-5.6 Sol Pro | Grok 4.20 | Leader |
|---|---|---|---|
| Design Arena: websites | Not measured | 1229 | Only Grok 4.20 measured |
| Design Arena: UI components | Not measured | 1199 | Only Grok 4.20 measured |
| Design Arena: game dev | Not measured | 1192 | Only Grok 4.20 measured |
| Design Arena: data viz | Not measured | 1217 | Only Grok 4.20 measured |
| Design Arena: 3D | Not measured | 1193 | Only Grok 4.20 measured |
| Design Arena: all code categories | Not measured | 1221 | Only Grok 4.20 measured |
| Design Arena: SVG | Not measured | 1164 | Only Grok 4.20 measured |
| Design Arena: ASCII art | Not measured | 1174 | Only Grok 4.20 measured |
| Neither model has a result on the other 1 board here | |||
GeneralLike-for-likePublic boards, shown as published, kept out of the index20
| Benchmark | GPT-5.6 Sol Pro | Grok 4.20 | Leader |
|---|---|---|---|
| SAGE (Vals AI) | Not measured | 38.2% | Only Grok 4.20 measured |
| MedScribe (Vals AI) | Not measured | 63.4% | Only Grok 4.20 measured |
| Vals Multimodal Index | Not measured | 39.1% | Only Grok 4.20 measured |
| IFBench | Not measured | 81.2% | Only Grok 4.20 measured |
| Long context reasoning (AA-LCR) | Not measured | 69.0% | Only Grok 4.20 measured |
| DTBench | 96.0% | 90.1% | GPT-5.6 Sol Pro |
| LMCA | 59.2% | 38.7% | GPT-5.6 Sol Pro |
| CL-bench | Not measured | 22.2% | Only Grok 4.20 measured |
| CL-bench Life | Not measured | 11.9% | Only Grok 4.20 measured |
| Neither model has a result on the other 37 boards here | |||
Image generationNot comparablePublic boards, shown as published, kept out of the index0 boards, none shared
| Benchmark | GPT-5.6 Sol Pro | Grok 4.20 | Leader |
|---|---|---|---|
| Neither model has a result on 5 boards here | |||
What each workload costs
Three fixed token mixes at each model's listed price, so per-token rates become a bill.
Chat turn
1K input + 500 output tokens
Grok 4.20 costs less
Repository review
50K input + 3K output tokens
Grok 4.20 costs less
Agent loop
200K input + 10K output tokens
Grok 4.20 costs less
Listed OpenRouter rates, without cache or batch discounts. A workload that does not fit a model's context window would need splitting.
Specification differences
The leading value in a row is marked; a row with a missing value names no leader. Our two rows are marked in red.
| Specification | OpenAI GPT-5.6 Sol Pro | SpaceXAI Grok 4.20 |
|---|---|---|
| Maker | OpenAI | xAI |
| Weights | No public weights listed | No public weights listed |
| Released | July 9, 2026 | March 31, 2026 |
| Context window | 1.05M | 2M |
| Input $/Mtok | $4.00 | $1.25 |
| Output $/Mtok | $20.00 | $2.50 |
| Coding index | Not benchmarked | 33.3 |
| Independent measurements behind it | 0 | 2 |
| Cost per solved task | Not computable | $0.72 |
| Source | OpenRouter listing | OpenRouter listing |
Questions
Is GPT-5.6 Sol Pro better than Grok 4.20 for coding?
Only Grok 4.20 has a coding score, 33.3 on the Vibe Coding Index; GPT-5.6 Sol Pro has none, so the two cannot be ranked on coding. Pick GPT-5.6 Sol Pro for work measured by WeirdML or DTBench, where it leads.
Which is cheaper, GPT-5.6 Sol Pro or Grok 4.20?
GPT-5.6 Sol Pro costs $4.00 per million input tokens and $20.00 per million output tokens; Grok 4.20 costs $1.25 and $2.50. Cost per solved task is known for Grok 4.20 only.
Which has the bigger context window, GPT-5.6 Sol Pro or Grok 4.20?
Grok 4.20, with 2M tokens against 1.05M.
How many benchmarks is the GPT-5.6 Sol Pro vs Grok 4.20 comparison based on?
3 benchmarks have a result for both models as of October 21, 2026. GPT-5.6 Sol Pro's coding index rests on 0 independent benchmarks and Grok 4.20's on 2. Where only one model has a result, the page says so instead of naming a winner.