Grok 4.6 vs GPT-5.6 Sol: Coding, Agents, Context, and API Cost
A source-checked comparison of Grok 4.6 and GPT-5.6 Sol across coding and agent benchmarks, context limits, reasoning controls, official API prices, long-context rules, and production fit.
xAI released Grok 4.6 on August 12, 2026, putting it directly into the same coding-agent conversation as OpenAI's GPT-5.6 Sol. The useful question is not which launch chart has the taller bar. It is which model completes your workload with fewer retries, less context growth, and an acceptable bill.
The short answer: Grok 4.6 is the stronger price-first default for iterative coding and agent loops; GPT-5.6 Sol is the stronger capability-first choice for the hardest tool-heavy work, very large contexts, and workflows that use OpenAI's newer agent controls. Neither is a universal winner.
All specifications and prices below were checked against official vendor documentation on August 15, 2026. Benchmark figures are vendor-reported, not independent Modelflare test results.
Quick answer
- Pick Grok 4.6 when output cost matters, your working context stays below 500K, and you want a capable coding or research agent without paying flagship output rates.
- Pick GPT-5.6 Sol when the task benefits from a 1.05M context window,
maxreasoning, Pro mode, persisted reasoning, Programmatic Tool Calling, or OpenAI's multi-agent beta. - Do not choose from token price alone. A cheap run that retries twice can cost more than an expensive run that lands the change once.
- For production routing, test both on the same repositories, tools, timeouts, and acceptance criteria.
For the xAI-specific API contract, pricing boundary, and migration checklist, read the Grok 4.6 API guide.
Grok 4.6 vs GPT-5.6 Sol specifications
| Property | Grok 4.6 | GPT-5.6 Sol |
|---|---|---|
| Release | August 12, 2026 | July 9, 2026 |
| Exact API model ID | grok-4.6 |
gpt-5.6-sol (gpt-5.6 alias) |
| Context window | 500,000 tokens | 1,050,000 tokens |
| Maximum output | No fixed limit listed by xAI; request and context limits still apply | 128,000 tokens |
| Modalities | Text and image input; text output | Text and image input; text output |
| Reasoning effort | low, medium, high, xhigh | none, low, medium, high, xhigh, max |
| API formats | Responses, Chat Completions | Responses, Chat Completions |
| Documented agent features | Function calling, structured outputs, web/X search, code execution | Function calling, structured outputs, hosted tools, persisted reasoning, Programmatic Tool Calling, multi-agent beta, Pro mode |
Parameter counts are absent because neither vendor publishes an authoritative parameter count for these production models. Treat third-party numbers as estimates, not API specifications.
Official API pricing and long-context cost
The headline rates per one million tokens are:
| Price component | Grok 4.6 | GPT-5.6 Sol |
|---|---|---|
| Input | $2.00 | $5.00 |
| Cached input | $0.50 | $0.50 |
| Output | $6.00 | $30.00 |
| Long-context boundary | At or above 200K prompt tokens | Above 272K input tokens |
| Long-context rule | $4 input, $1 cached input, $12 output | 2x input and 1.5x output for the full request |
Worked examples using official token rates:
| Request shape | Grok 4.6 | GPT-5.6 Sol |
|---|---|---|
| 100K input + 5K output | $0.23 | $0.65 |
| 220K input + 10K output | $1.00 | $1.40 |
| 300K input + 10K output | $1.32 | $3.45 |
These examples exclude built-in tool fees, cache writes, fast or priority service tiers, retries, and gateway pricing. Grok crosses its higher rate at 200K prompt tokens; Sol crosses at more than 272K input tokens. Both rules apply to the entire qualifying request, so context compaction can change the bill materially.
The cached-input headline is equal at $0.50 per million before long-context adjustments. The large gap is output: Sol's standard output rate is five times Grok 4.6's. That matters for agents that produce long patches, tool arguments, test logs, and recovery turns.
What the launch benchmarks actually show
xAI's Grok 4.6 announcement publishes a direct table against GPT-5.6 Sol. It compares Grok 4.6 High with GPT-5.6 Sol Max and says competitor figures come from published system cards or benchmark leaderboards.
| Evaluation | Grok 4.6 High | GPT-5.6 Sol Max |
|---|---|---|
| Artificial Analysis Intelligence Index | 61 | 61 |
| GDPVal-AA v2 | 1753 | 1728 |
| CursorBench v3.2 | 69.9% | 67.2% |
| DeepSWE v1.1 | 65.9% | 73.0% |
| FrontierCode v1.1 Extended | 61.3% | 60.6% |
| APEX-Agents | 57.5% | 56.7% |
| Terminal-Bench v3.0 | 26.0% | 34.6% |
| AA-Briefcase | 1577 | 1502 |
Read this as a workload map, not a final ranking. On xAI's table, Grok leads several knowledge-work and coding-agent measures, while Sol leads DeepSWE and Terminal-Bench. The reasoning settings differ, the data comes from a vendor launch post, and benchmark harnesses do not reproduce your repository, tools, permissions, or definition of done.
Where each model is meaningfully different
Grok 4.6's practical advantage is simpler economics for long agent trajectories. Its standard input rate is lower, its output rate is much lower, and xAI explicitly trained the model for multi-step research, codebase work, web development, and self-verification. It also offers an xhigh reasoning level and a fast service variant.
GPT-5.6 Sol has the broader execution surface. Its context window is more than twice as large, max adds another reasoning level, and Pro mode spends more model work on one answer. The Responses API can preserve reasoning across turns, execute eligible tool calls programmatically, and coordinate subagents through a beta multi-agent feature. Those are real differences when the harness can use them; they do not help if your client only sends ordinary Chat Completions requests.
Which model should you choose?
| Workload | Better starting point | Why |
|---|---|---|
| Frequent coding iterations with controlled context | Grok 4.6 | Lower input and output rates; strong launch results on several coding-agent evals |
| Repository or document context above 500K | GPT-5.6 Sol | 1.05M context window |
| Output-heavy agents | Grok 4.6 | $6/M standard output versus $30/M |
| Deep terminal and software-engineering tasks | GPT-5.6 Sol | Leads DeepSWE and Terminal-Bench in xAI's published comparison |
| Programmatic tool orchestration or multi-agent execution | GPT-5.6 Sol | Native Responses features documented by OpenAI |
| Cost-sensitive fallback behind a premium model | Grok 4.6 | Lower retry and output exposure while retaining frontier-class capability |
| High-stakes production changes | Test both | Task success, review findings, latency, and rollback safety matter more than one benchmark |
A sensible router does not need one permanent winner. Use the cheaper model for routine work, escalate tasks that fail a clear acceptance gate, and keep the final model, attempts, usage, latency, and charge visible.
Call both models through one Modelflare endpoint
At the production catalog check on August 15, 2026, Modelflare listed both exact model IDs with OpenAI-compatible Responses and Chat Completions support. grok-4.6 was available in the grok-award and grok-stable groups; gpt-5.6-sol was available in the corresponding OpenAI groups and additional eligible groups.
The request stays the same; only MODEL_ID changes:
export MODELFLARE_API_KEY="<YOUR_MODELFLARE_API_KEY>"
export MODEL_ID="grok-4.6" # or gpt-5.6-sol
curl -sS https://origin.modelflare.dev/v1/responses \
-H "Authorization: Bearer $MODELFLARE_API_KEY" \
-H "Content-Type: application/json" \
-d "{
\"model\": \"$MODEL_ID\",
\"input\": \"Review this patch for correctness, race conditions, and billing regressions. Return only actionable findings.\"
}"
Check the live Grok 4.6 pricing page and GPT-5.6 Sol pricing page before budgeting. Group access, multipliers, routes, and upstream prices can change. A catalog entry also does not prove that every vendor-native tool or beta field is translated by an OpenAI-compatible adapter.
Run a useful comparison on your own workload
Use the same evaluation contract for both models:
- Select 10–30 representative tasks, including at least a few failures from production.
- Freeze the repository state, prompt, tool schema, timeout, and permission boundary.
- Run the same reasoning class where possible and record any unavoidable mismatch.
- Measure accepted tasks, review findings, wall time, input, cached input, output, tool calls, retries, and total charge.
- Separate first-pass success from success after recovery; retries are part of model cost.
- Inspect failures by type: wrong assumption, missed edge case, invalid tool call, incomplete patch, or excessive context growth.
- Choose the route by cost per accepted task, not cost per token.
For long-running agents, also test immediately below and above each model's long-context boundary. A workload that slowly grows past 200K or 272K can change the comparison without any code change.
Frequently asked questions
Is Grok 4.6 better than GPT-5.6 Sol for coding?
Not across every coding task. xAI's launch table shows Grok 4.6 ahead on CursorBench and slightly ahead on FrontierCode, while GPT-5.6 Sol leads DeepSWE and Terminal-Bench. Use Grok as a cost-efficient starting point and test Sol on the hardest repository and terminal tasks.
Is GPT-5.6 Sol worth the higher API price?
It can be when the larger context, deeper reasoning controls, or Responses-only agent features improve first-pass success. If your workflow does not use those capabilities, the five-times-higher standard output rate is harder to justify.
Which one is cheaper for long conversations?
Usually Grok 4.6 at official list price, especially when output is large. However, Grok's long-context pricing starts earlier at 200K prompt tokens. Measure context growth, cache hits, retries, and output together.
Can one API key switch between them?
Yes on Modelflare when the key has access to eligible groups for both models. Keep the exact model IDs, verify the supported endpoint, and run a non-sensitive request before changing production traffic.
Official sources and update log
Primary sources:
- xAI: Introducing Grok 4.6
- xAI developer guide: Grok 4.6
- xAI API pricing
- OpenAI: GPT-5.6 Sol model page
- OpenAI: GPT-5.6 model guidance
- OpenAI: GPT-5.6 launch
Update log:
- August 15, 2026: Initial comparison. Official specifications, prices, long-context rules, launch benchmark table, and Modelflare catalog availability checked.