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Relaykit

OpenAI · GPT · Flagship

GPT-5.6 Sol

High-effort GPT reasoning model for difficult multi-step problems.

Model id

gpt-5.6-sol

Price per 1M tokens

Input
$5.50
Output
$33.00
Cached input
$0.5590% below input

Output is 6× the input rate. $1 covers about 45 prompts of 1,000 input + 500 output tokens. 1 credit = $1 of usage. All rates

Ways to pay

  • Pay as you goPrepaid balance at the rates above, top-ups from $3
  • Pro $5/monthWeekly allowance of about 148.4k uncached input tokens of this model
  • Plus $9/monthWeekly allowance of about 279.3k uncached input tokens of this model, 2% below the rates above
  • Max $29/monthWeekly allowance of about 925.1k uncached input tokens of this model, 4% below the rates above

Plans are opening soon; until then every model is pay as you go. How plans will work

Start using GPT-5.6 Sol

Set RELAYKIT_API_KEY to a key from your console, then run any example. Streaming is on so long answers are not cut off by idle-connection timeouts.

curl https://api.oneaiapikey.com/v1/chat/completions \
  -H "Authorization: Bearer $RELAYKIT_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-5.6-sol",
    "stream": true,
    "messages": [{"role": "user", "content": "In two sentences, when should I use hard reasoning?"}]
  }'
import os
from openai import OpenAI

client = OpenAI(
    base_url="https://api.oneaiapikey.com/v1",
    api_key=os.environ["RELAYKIT_API_KEY"],
)

stream = client.chat.completions.create(
    model="gpt-5.6-sol",
    messages=[{"role": "user", "content": "In two sentences, when should I use hard reasoning?"}],
    stream=True,  # recommended for long outputs
)
for chunk in stream:
    if chunk.choices and chunk.choices[0].delta.content:
        print(chunk.choices[0].delta.content, end="", flush=True)
import OpenAI from "openai";

const client = new OpenAI({
  baseURL: "https://api.oneaiapikey.com/v1",
  apiKey: process.env.RELAYKIT_API_KEY,
});

const stream = await client.chat.completions.create({
  model: "gpt-5.6-sol",
  messages: [{ role: "user", content: "In two sentences, when should I use hard reasoning?" }],
  stream: true,
});

for await (const chunk of stream) {
  process.stdout.write(chunk.choices[0]?.delta?.content ?? "");
}

More: quickstart · API reference · try it in Chat first

Overview

When GPT-5.6 Sol fits

GPT-5.6 Sol is a flagship model from OpenAI, available here under the exact model id “gpt-5.6-sol”. It sits at the top of the GPT line-up, so it is the one to reach for when answer quality matters more than cost per token.

It costs $5.50 per million input tokens and $33 per million output tokens, so output is 6× the input rate. Long answers are therefore the main cost driver: cap max tokens, ask for diffs instead of whole files, and keep reasoning effort proportional to the task. With a 3:1 input-to-output mix it is the highest-priced of the 11 models on this site, so use it where it clearly earns that.

Cached input bills at $0.55 per million tokens, 90% below the standard input rate. Workloads that resend the same system prompt, tool definitions and files on every turn, coding agents in particular, get the most from this.

It is served through the OpenAI-compatible format at https://api.oneaiapikey.com/v1, so any SDK or tool that lets you set a custom base URL, for example Codex CLI, Cursor and Cline, can use it. It is not offered on the Anthropic Messages endpoint; pick an Anthropic-format model for Claude Code.

Cost examples

What a workload costs

Worked from the published rates, with the arithmetic shown. Real numbers depend on prompt size and how much the model writes.

Model your own traffic

  • 1M input + 200k output tokens

    1 × $5.50 + 0.2 × $33.00

    $12.10

  • 1,000 chat replies (1.5k in, 400 out each)

    1000 × (0.0015 × $5.50 + 0.0004 × $33.00)

    $21.45

    About 46 replies per credit

  • One agent turn (30k in, 24k of it cached, 2k out)

    0.006 × $5.50 + 0.024 × $0.55 + 0.002 × $33.00

    $0.1122

    $0.231 with no cache hits. Writing tokens into the cache bills 1.25× the input rate (2× for a 1-hour cache) when the provider reports cache writes

Works with

Compatible agents 7

Coding tools that speak the OpenAI format. Each guide sets the base URL, key and this model id.

Similar models

Same tier, other vendors

Same key, same balance. Switching is a change to the model field.

Compare side by sideAll models

Try GPT-5.6 Sol from a $3 top-up.

There is no sign-up credit: add $3 or more to your wallet and every request is billed at the rates above, with a receipt in your usage log.

GPT-5.6 Sol is developed by OpenAI. Model names and trademarks belong to their owners. Relaykit is an independent API gateway and is not affiliated with, endorsed by or sponsored by OpenAI.