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Start with GPT-6.1 Sol if it meets your quality bar: OpenAI positions it as near-Astra performance for complex work at lower API cost. Choose GPT-6 Astra when your tasks demand the strongest reasoning capability available and the additional token cost is justified. Because these are vendor positions—not proof of which model will work better on your codebase—run both on representative tasks before setting a default.

What is the practical difference between Sol and Astra?

OpenAI describes GPT-6 Astra as its most capable model for demanding work and GPT-6.1 Sol as a lower-cost option for complex work. The Sol model documentation calls it “Near-Astra performance for complex work at a lower cost.” That is OpenAI’s product positioning, not a measured guarantee that Sol will match Astra on a particular bug, feature, repository, or agent workflow.

The practical choice is therefore not simply “cheap versus good.” It is whether Sol can complete your work to the required standard, and whether any difference in accuracy, follow-up effort, or workflow reliability makes Astra worth its higher token rates.

How do their API prices and limits compare?

OpenAI’s 2026 model catalog lists these standard API token prices and limits:

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Model Input price Output price Context window Maximum output
GPT-6 Astra $10 per million tokens $50 per million tokens 1,050,000 tokens 128,000 tokens
GPT-6.1 Sol $2 per million tokens $10 per million tokens 1,050,000 tokens 128,000 tokens

At those standard rates, Sol’s listed input and output token prices are each one-fifth of Astra’s. The equal listed context and maximum-output limits mean these figures do not, by themselves, distinguish the models for workflows that need to submit a large codebase or request a long response.

OpenAI’s September 29, 2026 changelog also lists a Sol cached-input rate of $0.10 per million tokens for prompts up to 272K input tokens, alongside $2 input, $2.50 cache-write, and $10 output per million tokens. This is a separately qualified pricing detail, not a replacement for checking the current applicable rates: pricing can change, and total task cost depends on which tokens are billed at which rate as well as any applicable tool or processing charges.

Which model should you try first for coding?

Start with Sol for cost-conscious complex work

Sol is a sensible first candidate when you want to control API token costs and the task is complex enough to need a capable model. Try it on work such as diagnosing a real repository issue, implementing a feature with tests, or making a bounded multi-file change. Keep it as your default only if its results are correct and acceptable for your review process.

Escalate to Astra when the task warrants it

Try Astra when a task is unusually demanding, when Sol’s output does not meet your quality bar, or when your own comparisons show that Astra’s results justify the higher token spend. A more expensive model is not automatically a better choice for every task; a simple, well-specified edit may not need the most capable option.

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The available OpenAI material provides positioning, specifications, and pricing, but does not establish a directly comparable published Sol-versus-Astra coding and agent benchmark. There is consequently no evidence here to declare one a universal winner in code quality, agent reliability, or total workflow cost.

How should you compare them on an agent workflow?

Use the same task, repository or input files, tool permissions, and comparable settings for each model. Include realistic work rather than only short code-generation prompts: an agent may need to inspect files, choose a tool, make a change, run checks, and recover from an error. Record outcomes rather than assuming that a lower token price means a cheaper completed task.

  • Correctness: Did the implementation solve the issue or complete the requested workflow? Check tests, edge cases, and whether the change fits the project.
  • Repair effort: How many corrections, retries, or follow-up prompts did it take to reach an acceptable result?
  • Tool execution: Did it select the appropriate tools, use them successfully, and stay within your workflow boundaries?
  • End-to-end latency: How long did the full task take under your chosen settings, including tool calls and retries?
  • Total cost: Count input, cached input, output, and applicable tool or processing charges for the completed task—not just the nominal price of one token category.
  • Operational fit: Can your team access the model in the intended environment, and is any required beta capability acceptable?

Repeat the comparison across several representative tasks if you plan to use the model as a default. A result from one prompt is a poor basis for a team-wide choice, especially when the work varies in difficulty or depends on tools.

What API and agent integration should you plan for?

For GPT-6.1 Sol tool calling, OpenAI directs developers to the Responses API. The model documentation says Chat Completions is supported without tool calling. Sol’s listed tools include web search, file search, image generation, code interpreter, hosted shell, apply patch, skills, computer use, MCP, and tool search; confirm the live model documentation for the capabilities available to your particular setup.

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Sol supports reasoning-effort settings of low, medium, high, xhigh, and max; its model page says none and minimal are not supported. For a fair comparison, use settings that are available and appropriate for both runs, and record them alongside results so that a change in reasoning effort is not mistaken for a model difference.

OpenAI’s September 29, 2026 changelog says Sol supports multi-agent delegation through a Responses API request in beta. Treat that as a beta capability, not an assurance of general availability or stability. If delegation is central to your workflow, evaluate it separately from ordinary tool calling and decide whether beta behavior is acceptable for the work involved.

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Where can you use GPT-6.1 Sol?

Sol is documented for API access and eligible ChatGPT Work and Codex use; the Help Center says it is not available in regular ChatGPT conversations. Availability in Work or Codex depends on plan eligibility, workspace settings, and rollout access, so confirm the model appears in the specific environment and account you intend to use.

Billing also depends on how you access it: OpenAI’s Help Center says API-key use is billed at API pricing, while signing in with ChatGPT uses plan usage and billing. If a workflow needs API tool calling or a beta feature, verify that the chosen access path supports it before making Sol or Astra your default.

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How to make the final choice

  1. Choose representative tasks. Select real coding and agent work, including at least one task with tool use if that reflects your deployment.
  2. Run both models under comparable conditions. Keep inputs, tool access, and reasoning settings consistent where possible; record any differences.
  3. Review the completed work. Check correctness, tool behavior, repair effort, and end-to-end latency using the standards your team already applies.
  4. Calculate the cost of acceptable outcomes. Use the applicable current rates and token categories, plus relevant tool or processing charges; include retries and repair prompts.
  5. Set a default with an escalation path. Use Sol where its results meet your bar, and route tasks that fail your quality or workflow requirements to Astra or human review according to your policy.

This approach follows OpenAI’s recommendation to compare Sol and Astra on your own tasks while avoiding a conclusion the published information does not establish.

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