GPT-6.1 Sol API Guide: Model ID, Codex, Tool Calls

GPT-6.1 Sol, which OpenAI released on September 29, 2026, is in the Router One catalog as openai/gpt-6.1-sol (listed 2026-09-30), and the gateway also accepts OpenAI's own id, gpt-6.1-sol. It is served natively on POST /v1/responses — the wire format Codex CLI speaks — and on POST /v1/chat/completions. Point any OpenAI-compatible SDK or client at https://api.router.one/v1, send "model": "openai/gpt-6.1-sol" with a Router One key, and the request is routed, metered and logged like every other model. In the 2026-10-30 plan response, GPT-6.1 Sol is in the Premium models tier of Router One's Pro, Max and Ultra plans: on a plan its calls draw that tier's shared allowance, and calls beyond it, or without a plan, bill per token to your wallet. The GPT-6.1 Sol model page carries the live rates.

This guide covers what the catalog lists for the id, how OpenAI positions it against GPT-6 Sol, GPT-6 Astra and GPT-6.1 Terra, what changes in requests written for GPT-6 Sol, how billing and plans apply, what Codex CLI's new default model means for a Router One setup, and the first request on each endpoint. Catalog and plan observations are dated; the live catalog is the source of truth for a new request.

GPT-6.1 Sol at a glance

OpenAI's GPT-6.1 Sol model page (checked 2026-10-30) adds what the catalog does not carry. It describes "near-Astra performance for complex work at a lower cost", lists a maximum of 922,000 input tokens and 128,000 output tokens inside the 1,050,000-token window and an April 30, 2026 knowledge cutoff, and documents reasoning.effort values low, medium (the default), high, xhigh and max; the none and minimal efforts are not supported. The same page says "Tool calling requires the Responses API" and lists Chat Completions among its supported endpoints. Those are OpenAI's statements; what Router One vouches for is the catalog entry and how the gateway routes and bills it.

GPT-6.1 Sol, GPT-6 Sol or GPT-6 Astra?

OpenAI's launch post (September 29, 2026) calls GPT-6.1 Sol "an upgrade to GPT-6 Sol that nearly matches GPT-6 Astra's intelligence on agentic coding, computer use, and professional work", and its GPT-6 guide (checked 2026-10-30) places GPT-6 Astra at the highest intelligence, GPT-6.1 Sol at "balanced speed, cost, and intelligence" and GPT-6.1 Terra at "fast and efficient", for visual reasoning, precise computer use and clear, natural writing. The same guide says tool calling requires the Responses API for GPT-6 Astra, GPT-6.1 Sol and GPT-6.1 Terra. GPT-6 Sol's own model page now points to GPT-6.1 Sol as the newer Sol model. OpenAI reports that on DeepSWE v1.1 GPT-6.1 Sol matches GPT-6 Astra and beats GPT-6 Sol's best score by 6.4 percentage points at a lower reasoning effort, and that on OSWorld 2.0's offline set, at maximum reasoning effort, it scores 7 percentage points above GPT-6 Sol and comes within 2.1 percentage points of GPT-6 Astra. Those are OpenAI's results, not Router One measurements: run your own prompts before you move a workload.

What Router One adds to the choice:

• Which plan allowance. In the 2026-10-30 plan response, GPT-6.1 Sol and GPT-6 Sol count against the Premium models allowance on Pro, Max and Ultra — the tier that also lists GPT-5.6 Sol — while GPT-6 Astra counts against the Flagship models allowance, which only Max and Ultra carry; on Pro, GPT-6 Astra calls bill the wallet. GPT-6.1 Terra (openai/gpt-6.1-terra, listed as of the 2026-10-28 catalog) is in no plan tier as of the 2026-10-30 plan response, so it bills the wallet per token, plan or no plan.
• Posted rates. Router One posts its own rates for each id. The comparison pages below render the live figures side by side, so re-baseline cost when you switch.
• Same request path. GPT-6.1 Sol, GPT-6 Sol and GPT-6 Astra are all GPT-family ids served natively on /v1/responses, the Codex CLI path; Codex knows GPT-6.1 Sol from version 0.159.1 (see below).

Four comparison pages render the spec sheets and live rates side by side:

• GPT-6.1 Sol vs GPT-6 Sol — the generation step, and what the request rules change.
• GPT-6.1 Sol vs GPT-6 Astra — near-Astra on the Premium models allowance against GPT-6 Astra on the Flagship models allowance (2026-10-30 plan response).
• GPT-6.1 Sol vs Claude Sonnet 5.5 — the cross-vendor question; in the 2026-10-30 plan response GPT-6.1 Sol draws the Premium models allowance, while Claude Sonnet 5.5 is in no plan tier and bills the wallet.
• GPT-6.1 Terra vs GPT-6.1 Sol — OpenAI's fast, efficient model against GPT-6.1 Sol; in the 2026-10-30 plan response GPT-6.1 Sol draws the Premium models allowance, while GPT-6.1 Terra is in no plan tier and bills the wallet.

What changes from GPT-6 Sol in your requests

The key, base URL, endpoints, 1,050,000-token window and 272,000-token price line stay the same, and OpenAI's model pages list the same maximum input and output, input types and Responses tools for both models. What changes, per OpenAI's GPT-6 guide (migration quickstart, checked 2026-10-30):

• The model string. openai/gpt-6-sol becomes openai/gpt-6.1-sol.
• Reasoning effort. On OpenAI's own API, GPT-6.1 Sol supports neither none nor minimal. Where you used none, OpenAI suggests low; where you used minimal, it suggests starting at low and comparing results. Set it with reasoning.effort on Responses or reasoning_effort on Chat Completions; medium is the default. On /v1/chat/completions, Router One sends a reasoning_effort of none or minimal as low for openai/gpt-6.1-sol (since 2026-10-30, observed 2026-11-05); the response does not say so.
• Tool calls. GPT-6.1 Sol takes tool calls only on the Responses API, while GPT-6 Sol also runs function calls on Chat Completions when reasoning_effort is none. Code that sends tools on Chat Completions moves to /v1/responses.
• Sampling parameters. When the reasoning effort is not none — always, for GPT-6.1 Sol — remove temperature, top_p and top_logprobs, plus logprobs on Chat Completions; on Responses, take message.output_text.logprobs out of include.
• Knowledge cutoff. Per the two model pages, April 30, 2026, against GPT-6 Sol's April 20, 2026.

GPT-6 Sol remains listed: Router One still serves openai/gpt-6-sol, and OpenAI's deprecations page (checked 2026-10-30) names no retirement for it. The GPT-6 Sol API guide still applies to it.

How billing works

The model page shows two rate lines, and the total input tokens of one request select which one applies. At exactly 272,000 input tokens the standard line still applies. Strictly above it, the long-context line applies to the whole request — output included — not only to the tokens past the threshold. Monthly volume plays no part. OpenAI's model page documents the same 272K threshold and the same full-request rule for its own list prices, and Router One's long-context line mirrors it.

Reasoning output is billed at the model's posted output rate, with no separate reasoning line (pricing facts), so the reasoning effort is a cost lever as much as a quality one. The model page also lists a cached-input line; the prompt caching guide shows how to read cache counts in usage so input is not counted twice, the pricing methodology spells out the long-context rule, and the cost calculator applies it per request.

This guide prints no per-token figures because they go stale. The GPT-6.1 Sol model page shows both lines live, and the comparison pages above render the gap against GPT-6 Sol, GPT-6 Astra and Claude Sonnet 5.5.

Do subscription plans cover GPT-6.1 Sol?

Yes, as of the 2026-10-30 plan response: GPT-6.1 Sol is in the Premium models tier of Router One's Pro, Max and Ultra plans, together with GPT-6 Sol, GPT-5.6 Sol and the other models that tier lists. The tier's allowance per 30-day cycle (the pricing page lists each plan's allowance) is one pool shared by every model in the tier, not a separate allowance per model. A GPT-6.1 Sol request draws 1 request, or 2 when its total input is strictly above 272,000 tokens; the input count includes cached input once, and output does not count. Calls beyond the cycle's allowance bill the wallet at the posted rates. GPT-6 Astra sits in the Flagship models tier that only Max and Ultra carry. Plan model lists change, and the pricing page shows the live ones.

Codex CLI: the new default model and the one-line switch

Per its release notes, Codex CLI 0.159.1 (September 29, 2026) made GPT-6.1 Sol the default model of its bundled model list. That default applies only when config.toml names no model: per the Codex models docs (checked 2026-10-30), Codex uses a recommended model when you do not specify one. The Router One one-click install writes model = "gpt-5.6-sol", so a setup it wrote stays on GPT-5.6 Sol after the update. A config.toml you wrote by hand without a top-level model line picks up the new default — add one above the [model_providers] table, for example model = "gpt-5.6-sol".

To run GPT-6.1 Sol in Codex, set model = "gpt-6.1-sol" in ~/.codex/config.toml — the bare name from Codex's own model list, which the gateway resolves to openai/gpt-6.1-sol — and keep wire_api = "responses" on the provider. That needs Codex 0.159.1 or later: per the openai/codex source (checked 2026-10-30), 0.159.0 and earlier have no gpt-6.1-sol entry in their bundled model list and run an unknown name on generic fallback metadata, so update with npm install -g @openai/codex first. With a custom provider such as Router One's, Codex takes GPT-6.1 Sol's settings from its bundled model list, which gives it a 272,000-token context window by default (per the openai/codex source, rust-v0.166.0, checked 2026-10-30).

On a Pro, Max or Ultra plan, GPT-6.1 Sol counts against the Premium models allowance (as of the 2026-10-30 plan response), and moving Codex from gpt-5.6-sol to gpt-6.1-sol keeps it on the same allowance: in the 2026-10-30 plan response gpt-6.1-sol, gpt-6-sol and gpt-5.6-sol are all in the Premium models tier of the Pro, Max and Ultra plans, so each request Codex sends to one of them draws from that tier's shared allowance, and calls beyond it bill the wallet at the posted rates. Without a plan, every request Codex sends bills the wallet at GPT-6.1 Sol's posted rates (model page). Per the Codex source (rust-v0.166.0, checked 2026-10-30), Codex 0.159.1 and later may show a startup tip that recommends GPT-6.1 Sol; the tip does not change your model. The "Meet GPT-6 Sol" upgrade prompt still targets gpt-6-sol. The Codex CLI in China page has the full config, and the Codex and Responses API page explains why relays without the Responses wire format fail with Codex.

Send the first request

1. Create a key. Dashboard → API Keys → Create Key. Keys look like sk-.... For a trial, give the key a maxSpend cap: it cannot charge your wallet past that amount, and your other keys keep working (per-key cost tracking).
2. Keep a wallet balance or a plan. On Pro, Max or Ultra, GPT-6.1 Sol calls draw from the Premium models allowance first (2026-10-30 plan response); without a plan, and beyond the allowance, they bill the wallet — top up in Dashboard → Deposit.
3. Set the base URL to https://api.router.one/v1 in any OpenAI-compatible SDK or client.
4. Call the model. The examples use the catalog id openai/gpt-6.1-sol and set an explicit output cap.

Responses, the native path, with the reasoning effort set explicitly (medium is the vendor default):

curl https://api.router.one/v1/responses \
  -H "Authorization: Bearer sk-your-api-key" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-6.1-sol",
    "reasoning": {"effort": "medium"},
    "max_output_tokens": 25000,
    "input": "List three risks of a whole-request price tier for an agent loop."
  }'

Tool calls go on this endpoint. A function tool in the Responses format:

curl https://api.router.one/v1/responses \
  -H "Authorization: Bearer sk-your-api-key" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-6.1-sol",
    "reasoning": {"effort": "low"},
    "max_output_tokens": 25000,
    "tools": [{
      "type": "function",
      "name": "get_order_status",
      "description": "Look up the status of an order by its id.",
      "parameters": {
        "type": "object",
        "properties": {"order_id": {"type": "string"}},
        "required": ["order_id"]
      }
    }],
    "input": "Where is order 8812?"
  }'

When the output contains a function_call item, run the function and send its result back as a function_call_output item with the same call_id; OpenAI's reasoning guide recommends passing back the reasoning items from that turn as well.

Chat Completions, for clients that send it — without tools, as OpenAI's model page specifies:

curl https://api.router.one/v1/chat/completions \
  -H "Authorization: Bearer sk-your-api-key" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-6.1-sol",
    "max_completion_tokens": 25000,
    "messages": [{"role": "user", "content": "List three risks of a whole-request price tier for an agent loop."}]
  }'

The same Responses call from the OpenAI Python SDK — only base_url and the key change:

from openai import OpenAI

client = OpenAI(
    base_url="https://api.router.one/v1",
    api_key="sk-your-api-key",
)

response = client.responses.create(
    model="openai/gpt-6.1-sol",
    reasoning={"effort": "medium"},
    max_output_tokens=25000,
    input="List three risks of a whole-request price tier for an agent loop.",
)
print(response.status, response.output_text)
print(response.usage)

Rules that hold on both endpoints:

• Set an output cap on every request. Reasoning tokens count toward the output cap; OpenAI suggests reserving at least 25,000 tokens for reasoning and outputs when you start (reasoning guide, checked 2026-10-30). On the Responses API, per the same guide, a response that reaches the cap comes back with status: "incomplete", possibly before any visible text. On Router One's Chat Completions, max_tokens and max_completion_tokens both set this cap (if both are sent, max_completion_tokens wins); on the Responses API it is max_output_tokens.
• Leave out the sampling parameters. No temperature, top_p, top_logprobs or logprobs, as listed above.
• Stream long work. stream: true returns output as it is generated, on either endpoint (streaming guide).
• Stay off /v1/messages. Sending the id there returns HTTP 400 before any model is called, and the message says the model must be called via /v1/chat/completions. The API compatibility facts state the endpoint rule per family.

5. Read the trace. Dashboard → Logs shows each call with model, input and output tokens, cost, latency and status (per-request observability). Retryable upstream failures are absorbed by automatic fallback across the candidate routes for the same model; a GPT-6.1 Sol request is never answered by a different model.

Other coding tools

Coding agents send tools on almost every turn, and per OpenAI's GPT-6.1 Sol model page (checked 2026-10-30) the model takes tool calls only on the Responses API, so agent work with it needs a client that sends Responses requests. Before you point a tool at it, check which protocol that tool sends: the tool table in GPT-6 Sol in Codex CLI, Cursor, Cline and OpenCode lists the request path per tool. Claude Code cannot call GPT-6.1 Sol: it sends Anthropic Messages requests, and /v1/messages serves Claude-family and DeepSeek ids only.

From mainland China

Requests reach api.router.one from mainland China without a VPN, on the same key and base URL. Top up with a card or Alipay through one hosted checkout, or with USDT/USDC on six chains (Tron, BSC, Ethereum, Polygon, Base, Arbitrum). No US credit card required. Pricing starts as low as 10% of official provider list prices (up to 90% off) on select models; the GPT API page and each model page show the rate for a given id. For Codex CLI, see Codex CLI in China.

FAQ

What is the model id for GPT-6.1 Sol on Router One? openai/gpt-6.1-sol. The gateway also accepts OpenAI's own id, gpt-6.1-sol, which is the name to use in Codex CLI. The hyphenated gpt-6-1-sol in the model page address is the page slug, not a model id. In the 2026-10-30 plan response the model is in the Premium models tier of Pro, Max and Ultra, and either id draws from that allowance on a plan.

Is GPT-6.1 Sol included in Router One subscription plans? Yes, in the Premium models tier: in the 2026-10-30 plan response, Pro, Max and Ultra list GPT-6.1 Sol there, beside GPT-6 Sol and GPT-5.6 Sol, so its calls draw from the tier's shared allowance — 2 requests when the input is above 272,000 tokens — and calls beyond it bill the wallet. GPT-6 Astra is in the Flagship models tier of Max and Ultra. The pricing page shows the live plan model lists.

Codex CLI 0.159.1 made GPT-6.1 Sol its default model. Does my Router One setup switch? Only if config.toml names no model. Per the Codex models docs (checked 2026-10-30), Codex uses a recommended model when you do not specify one, and per the 0.159.1 release notes, 0.159.1 and later default to GPT-6.1 Sol. The Router One one-click install writes model = "gpt-5.6-sol", so it stays on GPT-5.6 Sol. On a plan, that makes no difference to the allowance: in the 2026-10-30 plan response, both models are in the Premium models tier. A hand-written config.toml without a top-level model line should still get one, so the next change of Codex's default does not move it to a model in another tier. Codex may also show a startup tip about GPT-6.1 Sol, which does not change the model.

What changes from GPT-6 Sol in my requests? Per OpenAI's GPT-6 guide (checked 2026-10-30): the model string; the reasoning effort, since on OpenAI's own API GPT-6.1 Sol supports neither none nor minimal (OpenAI suggests low); tool calls, which GPT-6.1 Sol takes only on the Responses API; and temperature, top_p and top_logprobs (plus logprobs on Chat Completions), which have to go. The key, base URL, the 1,050,000-token window and the 272,000-token price line stay the same.

Can I call tools on Chat Completions with GPT-6.1 Sol? Not per OpenAI: its GPT-6.1 Sol model page (checked 2026-10-30) says "Tool calling requires the Responses API" and lists Chat Completions among its supported endpoints. Send tool-using requests to /v1/responses, where Router One serves GPT models natively, and keep Chat Completions for requests without tools.

Does the 272K price line apply to GPT-6.1 Sol? Yes. Its model page shows two rate lines: exactly at 272,000 input tokens the standard line applies; strictly above it, the long-context line applies to the whole request, output included. Monthly usage does not select the line.

Is GPT-6 Sol being retired? Not as of 2026-10-30: OpenAI's deprecations page names no retirement for it. Router One still lists openai/gpt-6-sol, and the GPT-6 Sol API guide covers it.

Can Claude Code call GPT-6.1 Sol? No. Claude Code sends Anthropic Messages requests to /v1/messages, which serves Claude-family and DeepSeek ids only; a GPT id there returns HTTP 400 before any model is called.

How much does GPT-6.1 Sol cost through Router One? Per token, at the posted rates on the GPT-6.1 Sol model page: two lines, with reasoning billed as output. This guide prints no per-token figures because they go stale; the comparison pages render the live gap against GPT-6 Sol, GPT-6 Astra and Claude Sonnet 5.5. On Pro, Max and Ultra, calls inside the Premium models allowance draw plan requests instead (2026-10-30 plan response).

Is there no GPT-6.1 Astra? OpenAI's model catalog (checked 2026-10-30) has no GPT-6.1 Astra entry, and its GPT-6 guide lists GPT-6.1 Sol beside GPT-6 Astra. Router One lists GPT-6 Astra (openai/gpt-6-astra) and GPT-6.1 Sol (openai/gpt-6.1-sol); the live catalog at /models is the source of truth.

Next steps

• Open the GPT-6.1 Sol model page for the live rates, both price lines and the endpoint list.
• Compare it with GPT-6 Sol, GPT-6 Astra or Claude Sonnet 5.5.
• Staying on GPT-6 Sol? The GPT-6 Sol API guide and GPT-6 Sol in Codex CLI, Cursor, Cline and OpenCode cover it.
• Weighing GPT-6 Astra instead? The GPT-6 Astra API guide covers its model id, Codex setup and the Flagship plan quota on Max and Ultra.
• Considering GPT-6.1 Terra? The GPT-6.1 Terra API guide covers its model id, wallet billing and what changes from GPT-6.1 Sol.
• Considering Luna, the GPT-6 model OpenAI positions for focused, high-volume tasks? The Luna API guide covers its model id, wallet billing and OpenAI's tool rules for it.
• Set up Codex CLI with Codex CLI in China and the Codex and Responses API page.
• Check which models each plan covers on the pricing page.
• See September's other catalog changes in the September 2026 new-model guide.