---
title: "Claude Opus 5.5 vs GPT-6 Sol: Which One to Use for Coding"
description: "Claude Opus 5.5 and GPT-6 Sol launched the same day. Pricing, context windows and benchmarks from the official pages, why the launch benchmarks can't be compared, the cheap GPT-6 Luna option, and a 20-minute test to pick your own default. Checked 24 September 2026."
date: "2026-09-24"
type: "build"
tags: []
legacy: true
---
<p>
        You commented <strong>MODELS</strong>, so here's the breakdown.
        Anthropic released Claude Opus 5.5 and OpenAI released GPT-6 Sol and
        GPT-6 Luna on the same day, 22 September 2026. Both companies cut prices
        and both pitched their model at coding agents.
      </p>
      <p>
        Every number below comes from the official model pages. I checked them
        on 24 September 2026.
      </p>

      <div class="highlight">
        <p style="margin-bottom: 0">
          <strong>The short version:</strong> Sol costs half as much as Opus 5.5
          per token. Luna is the one most students should look at first, because
          Free and Go users get it in the Codex desktop app. Don't pick between
          Opus and Sol from launch-day benchmarks. Give both the same task on
          your own code.
        </p>
      </div>

      <h2>The numbers</h2>
      <table>
        <thead>
          <tr>
            <th></th>
            <th>Claude Opus 5.5</th>
            <th>GPT-6 Sol</th>
            <th>GPT-6 Luna</th>
          </tr>
        </thead>
        <tbody>
          <tr><td>Input, per 1M tokens</td><td>$4</td><td>$2</td><td>$0.10</td></tr>
          <tr><td>Output, per 1M tokens</td><td>$20</td><td>$10</td><td>$0.50</td></tr>
          <tr><td>Cached input, per 1M tokens</td><td>$0.20</td><td>$0.20</td><td>&nbsp;</td></tr>
          <tr><td>Context window</td><td>1M tokens</td><td>1.05M tokens</td><td>&nbsp;</td></tr>
          <tr><td>Max output</td><td>128K tokens</td><td>128K tokens</td><td>&nbsp;</td></tr>
          <tr><td>Model ID</td><td><code>claude-opus-5-5</code></td><td><code>gpt-6-sol</code></td><td>&nbsp;</td></tr>
        </tbody>
      </table>
      <p>
        Sources:
        <a href="https://platform.claude.com/docs/en/models/overview">Claude models overview</a>,
        <a href="https://developers.openai.com/api/docs/models/gpt-6-sol">GPT-6 Sol model page</a>,
        <a href="https://openai.com/index/introducing-gpt-6-sol-and-luna/">OpenAI's launch post</a>.
        The blank cells are numbers I couldn't find on an official page, so I
        didn't fill them in.
      </p>

      <h2 id="opus">1. Claude Opus 5.5</h2>
      <p class="repo-link">
        <a href="https://www.anthropic.com/claude-opus-5-5">anthropic.com/claude-opus-5-5</a>
      </p>
      <p>
        Anthropic says Opus 5.5 is 30% faster than Opus 5 and costs about 40%
        less to run on typical workloads. Per-token prices dropped 20% and
        cached reads dropped 60%. The numbers they highlight for coding and
        agents: Terminal-Bench 4.0 at 66.4%, CursorBench 4.0 at 57.8% and
        OSWorld 2.0 at 81.8%.
      </p>
      <p>
        If you use Claude Code you already have it. Opus 5.5 became the default
        model in Claude Code 2.1.280
        (<a href="https://releasebot.io/updates/anthropic">release notes</a>).
      </p>

      <h2 id="sol">2. GPT-6 Sol</h2>
      <p class="repo-link">
        <a href="https://openai.com/index/introducing-gpt-6-sol-and-luna/">openai.com/index/introducing-gpt-6-sol-and-luna</a>
      </p>
      <p>
        OpenAI's model for coding and agent work. It costs 50% less than the
        GPT-5.6 generation it replaces. It's in Codex for Plus, Pro, Business,
        Enterprise and Edu plans, and in GitHub Copilot on Pro+ and higher plans
        (<a href="https://github.blog/changelog/2026-09-22-openais-gpt-6-sol-and-gpt-6-luna-now-available/">GitHub changelog</a>).
      </p>
      <p>
        OpenAI's headline claim is that Sol comes within 1.1 points of Claude
        Fable 5's best score on DeepSWE v1.1 at roughly 80% lower cost.
      </p>

      <h2 id="luna">3. GPT-6 Luna, the cheap one people are missing</h2>
      <p>
        Luna costs $0.10 per million input tokens. Free and Go users get it in
        the Codex desktop app
        (<a href="https://community.openai.com/t/announcing-gpt-6-sol-and-gpt-6-luna-in-the-api-codex-and-chatgpt/1399925">OpenAI's announcement</a>),
        and it's on Copilot Pro. It's good enough for small scripts, tests,
        boilerplate and explaining code, which covers most of what you do in a
        college project.
      </p>

      <h2>Why the benchmarks don't settle it</h2>
      <p>
        Look at the numbers above again. Anthropic reports Terminal-Bench, OpenAI
        reports DeepSWE and AutomationBench. Neither launch post reports the
        other's benchmarks, so you can't put them side by side. Each company
        picked the tests it wins. The only comparison that tells you anything is
        one you run on your own code.
      </p>

      

      <h2>How to run your own test in 20 minutes</h2>
      <ol>
        <li>Pick one real bug or small feature from a project you've already built.</li>
        <li>Make two branches from the same commit, one per model.</li>
        <li>Give both the exact same prompt, once in Claude Code and once in Codex.</li>
        <li>
          Compare three things: the diff, how many times you had to correct it,
          and what it cost.
        </li>
        <li>Keep the branch you'd actually merge. That's your answer.</li>
      </ol>

      <h2>How I'd use them on a student budget</h2>
      <ul>
        <li><strong>Luna</strong> for the small everyday jobs: tests, renames, docs, quick scripts.</li>
        <li><strong>Opus 5.5 or Sol</strong> only for the hard parts: a migration, a gnarly bug, a feature that touches many files.</li>
        <li>
          <strong>Whichever wins your test</strong> as the default. Switching
          costs you a model menu, not a rewrite.
        </li>
      </ul>

      <p>
        If you want the harness side of this, read
        <a href="/blog/github-repos-that-make-claude-code-better">8 GitHub repos that make Claude Code 10x better</a>.
        A better model helps less than you'd think if the setup around it is
        weak.
      </p>

      <p>
        Follow
        <a href="https://www.instagram.com/avi_vashishta29/">@avi_vashishta29</a>
        for one practical AI dev tool a day.
      </p>